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📌Transcript debugger

📅December 14th, 2022

Summary: I'm making a case for a certain type of debugger.

More detail below.

A couple times people trying to get into ROM patching ask me what tool I use. I'll answer, although it's not the popular answer. It takes some getting used to because of type of debugging it is and for other reasons.

What I use for most of my patching stuff is Geiger's SNES debugger. It's a special build of Snes9x with a debugger bolted on.

Looks like this

The game, main debugger interface, and memory view are in different windows. You press the 'Breakpoints' button to get a pop-up dialog for setting those. Looks very Win32 ish.

Why not for everyone?

When I first started looking into debugging SNES it was a while ago, this was one of the best options available.

Since then, the world has moved on.

Despite the age of the SNES today, there is a lot of information out there sourced by fans and tools under active development.

Today, there are SNES debuggers that

  • have larger feature sets
  • have been tested more thoroughly to weed out issues
  • have interfaces that suit newer UI/UX paradigms
  • are actively developed
  • are open-source and so are easy to extend

The debugger has some 'personality traits' I've gotten used to working around. Here's a list of what they are in case you run into them.

Issue: Breakpoints don't hit after certain operations (e.g., save state load)
Workaround: Re-open the breakpoint window, and click OK.

Issue: Step Out doesn't step out to the expected place
Workaround: Don't rely on Step Out for function calls that straddle any interrupts.

Issue: 'Show Hex' (memory) window shows blank ROM on 1st open
Workaround: Choose something (e.g., RAM) 'viewing' dropdown then go back to ROM.

Issue: Emulator crash if you scroll too far down in the memory window
Workaround: Don't use invalid ranges. Don't try to scroll past the end of the range.

Issue: Can not view CGRAM or OAM
Workaround: Use a different debugger.

Issue: Can not view DBR or PBR
Workaround: Edit some code to push them (PHB/PHK) then PLA.

Software

The debugger isn't under active development anymore so things like the above list are what they are. I contacted Geiger asking for the source code. He responded wishing me well, and wouldn't give it to me for various reasons which is his perogative.

None of these were bad enough to block me, it's been alright.

They also weren't severe enough to be motivating to go in and fix them in this closed-source program.

Why I use it

Despite the above things, I still use it for a few reasons.

  • Habit. I know my way around it
  • The most complicated parts of what I need to do aren't actually through a debugger, (e.g., 'special diffing' of memory dumps), and a debugger could never do as good a job as flexible-function code.
  • Transcript-style debugging.

The biggest one is transcript debugging.

For transcript-style debugging see explanation below.

Transcript-style debugging

For ROM patching projects where the patch is a small targeted surface area, generally speaking you're not trying to recover source code.

Recovering source code so that you can work in it is something you can do if you really want. You can do it if it makes you happy. But it's not always crucial. It can even be a distraction. Be it in an assembly language or a higher-level language like C/C++, recovering source code can be unnecessary for your goal of a targeted change in behavior and can make the task way less efficient.

To get better at this kind of reverse-engineering task, and this is hard for a lot of people to hear-- you need to fall out of love with source code written in programming languages. This includes source-level debugging, it includes expressions of flow control, and this includes source code written in assembly languages.

Below is an example of a debugger listing not using source-level debugging, and using transcript-style debugging instead:

$80/BC3A 20 B0 C1    JSR $C1B0  [$80:C1B0]   A:0000 X:00A9 Y:0005 P:envmXdizc

$80/C1B0 64 6F       STZ $6F    [$00:006F]   A:0000 X:00A9 Y:0005 P:envmXdizc
$80/C1B2 A5 6C       LDA $6C    [$00:006C]   A:0000 X:00A9 Y:0005 P:envmXdizc
$80/C1B4 0A          ASL A                   A:3640 X:00A9 Y:0005 P:envmXdizc
$80/C1B5 88          DEY                     A:6C80 X:00A9 Y:0005 P:envmXdizc
$80/C1B6 F0 13       BEQ $13    [$C1CB]      A:6C80 X:00A9 Y:0004 P:envmXdizc
$80/C1B8 90 38       BCC $38    [$C1F2]      A:6C80 X:00A9 Y:0004 P:envmXdizc
$80/C1F2 86 00       STX $00    [$00:0000]   A:6C80 X:00A9 Y:0004 P:envmXdizc
$80/C1F4 A2 02       LDX #$02                A:6C80 X:00A9 Y:0004 P:envmXdizc
$80/C1F6 0A          ASL A                   A:6C80 X:0002 Y:0004 P:envmXdizc
$80/C1F7 88          DEY                     A:D900 X:0002 Y:0004 P:eNvmXdizc
$80/C1F8 F0 20       BEQ $20    [$C21A]      A:D900 X:0002 Y:0003 P:envmXdizc
$80/C1FA E8          INX                     A:D900 X:0002 Y:0003 P:envmXdizc
$80/C1FB 90 F9       BCC $F9    [$C1F6]      A:D900 X:0003 Y:0003 P:envmXdizc
$80/C1F6 0A          ASL A                   A:D900 X:0003 Y:0003 P:envmXdizc
$80/C1F7 88          DEY                     A:B200 X:0003 Y:0003 P:eNvmXdizC
$80/C1F8 F0 20       BEQ $20    [$C21A]      A:B200 X:0003 Y:0002 P:envmXdizC

"But isn't this source code in assembly language?" I heard this question before. I think this confusion comes from people who haven't done much forward engineering with assembly languages yet, forget reverse engineering.

The above is not source code, it's a debugger transcript.

Again, it's not source code, it's printout of what got executed, one instruction at a time.

Dead giveaways that it's not source code

  • Every line starts with an address
  • Every line ends with register state
  • There's a function call and then the stepped-into body immediately after. Not proper for source code
  • Some instructions are repeated, like $80/C1F6, $80/C1F7, $80/C1F8. This is a loop

Thinking it's source code is pretty uncharitable to the readability of source code, which usually uses more identifiers and comments and labels and stuff than this example has.

The transcript looks different from source code, and transcript debugging is different from source style debugging.

How is transcript debugging different?

Now that we know what transcripts are: transcript-style debugging is different from source-style, or traditional debugging.

See an example of source-style debugging, with No$sns:

There's a window. In the window, the local disassembly appears in a listing, with the current instruction highlighted in blue. The local disassembly shows instructions laid out in one contiguous block of memory.

Or, here's another debugger, bsnes:

Another example of source-style debugging. The disassembly listing is on the right, with the current instruction highlighted in blue. They go the extra mile and put dividing lines in at observed function boundaries. I don't think that can ever be 100% robust but it's nice regardless.

Or, here's Visual Studio 2019:

The instructions are listed out. The current instruction is highlighted with a yellow arrow to the left of it. There's some things that couldn't be disassembled so there's a placeholder with question marks.

These are all examples of source-style debugging. It's very popular.

Depending on the implementation, the listing in a source-style debugger can either be

  • a local disassembly where all surrounding memory gets interpreted as code, whether it actually is code or not, or
  • the result of a tracing, where only executed instructions appear in the listing, creating gaps

The former is a lot more common, as in all the above examples, although I've seen both.

By contrast, a transcript style debugger will look like this:

See, there are disjoint instructions, with those pairs circled in red.

Some instructions are listed more than once.

And register state is shown on each line. This platform doesn't have a ton of register space so that's honestly pretty manageable.

The transcript shows all branches with the branch taken, all registers with state at the time, all opcodes with their resolved argument, all loops are unrolled.

The kicker is that implementation of this debugger is dead simple and actually very dumb. It echoes each executed instruction to the output, along with the current register state. That's it.

Yet it is powerful and offers some advantages.

Advantage: history of register values

It's true pretty much all debuggers will show you register values, or variable/memory values at the current instruction. But what about 5 or 10 instructions ago?

You need to either have time-travel debugging, log it, or restart your program.

Some debuggers will cache the "last seen" way something executed (pointer argument, etc), and update it when that instruction is executed again. Great, you can see what was the last way something executed.

But what about the time before that? Or earlier? You can't easily put together a history of what happened unless you log these data points manually yourself.

For reverse-engineering object code with no source code, getting this history is really important in figuring out what happened. You might need to look for trends, look for a pattern, to get a sense of the higher level algorithm. Or you might want transcripts even with code you are familiar with, to get something like a time-travel trace on platforms where actual time-travel isn't available. There's strictly more information in the transcript than in the source-style listing.

"But, it's only outputting registers each line, not all of memory each line". That's true. Each line of the transcript is not a complete state of the machine. I think register state is the right tradeoff to suit most tasks. The exact choice will depend on the platform and the situation. If you're blessed with extensible transcript debugging, that'd probably be the best thing, so you could have like a "watch window" for each line. Generally for SNES, A/X/Y/P is perfectly fine.

Advantage: history of flow control

You can see a clear history of flow control. After all, that's useful. With a couple source-style debuggers, I've seen them do crazy things like try and draw a cute arrow denoting a function was stepped into.

With a transcript, you can see a history of how many times a loop ran, what index of a jump table was used, and which branches had the branch taken. If you save longer transcripts (e.g., with Geiger's SNES debugger's CPU log feature) you can also meaningfully diff transcripts with any text diffing tool of your choice to find divergent control flow like this.

With source-style debugging, you have no record-keeping of this unless you log it yourself, and you can easily miss what you're looking for.

Advantage: An edge case

This is a bad scenario and not something I've ever seen happen out in the wild.

But you could have it where the same memory is executed twice with the code interpreted in different ways, e.g., 8 bit versus 16 bit native mode.

I don't think a source style debugger could easily make sense of this. A transcript would show what happened clearly.

I made a proof of concept that does this and on testing it doesn't work well at all in a source-style debugger.

Advantage: Don't disassemble stuff that's not code

This is a big one, SNES games will often litter non-code throughout code.

For example of what I mean, consider the game NHL '94 for Super Nintendo, This is bsnes broken in NHL '94's graphics decompression

See the part outlined in red. Although there's no obviously illegal instructions, it looks suspicious. Why the CPY with such an arbitrary magic number address? Same with the EOR and the literal, what's up with that? Why the LDAs that immediately get overwritten?

The answer is this isn't code at all. It's data. This source-style debugger will disassemble everything in the neighborhood. That works great only so long as it actually is code. You hope it looks like obvious garbage code, so you can quickly spot it.

In this case, it's actually an array of short pointer offsets baked into the middle of object code. Those are supposed to be offsets, not instructions. If you're really observant you'll see that the preceding JMP $BEB8, X indexes into it and jumps based on an element. It's a hassle to spot this right away, and the debugger isn't doing anything to help you.

Here's another example in a different place

Again red outlined part is not actually code, it's data. This one's sneakier than the above because from a glance it looks less garbage compared to the last one. The big giveaway is SED which is not commonly used.

With transcripts, we don't have this problem. These garbage instructions aren't something you have to discern from non-garbage. Why? Because they don't get executed. They don't even appear.

Why is there data beside the code?

SNES is a different kind of execution environment from what some people are used to.

For the situation above, you might have the reaction "But I work in x86 a lot and I've never seen this before."

Well, x86-64 applications won't have data sprinkled in the code.

Why? Because Intel's architecture does really aggressive instruction prefetching, and the CPU has to know what's code versus what's data for that to work.

You can hear it from Intel themselves:

If (hopefully read-only) data must occur on the same page as code, avoid placing it immediately after an indirect jump. For example, follow an indirect jump with its mostly likely target, and place the data after an unconditional branch.

[...]

Always put code and data on separate pages.

Source: Intel's Optimization Guide

If you write source code that is compiled, at least for a Windows executable, the compiler will put object code in the .text segment and constant data in the .rodata segment- it'll do that for you.

Or if you write source code in x86 assembly language, generally you'd would use a directive like .CODE or .DATA to explicitly define what goes where. The details depend on which assembler you use and what exactly is it outputting.

The WDC 65xx-based CPU, on the other hand, is out there living its best life. Memory is just memory, doesn't matter what's where.

Since it doesn't matter at all, it's up to developer preference and convenience. In practice I do notice developers for 65xx platform dump data in the middle of their code like all the time. They'll bake data local in the same bank to take advantage of direct addressing, since if you put all data together it'd have to go in a different bank to fit. Or they're trying to save a MMU page change on certain computers where that matters (e.g., Foenix F256). Or they'll use a self-modified jump instruction instead of a jump table.

So if you work mostly in x86-64 or any other compiler toolchain with the same recommendation, that's one more reason why you probably go through life dealing with source style debuggers. No surprise data tripping you up. It's probably not something you ever think about.

With reverse-engineering on a platform like SNES the value of transcripts is more clear.

Recommendation

Geiger's SNES debugger is a transcript-style debugger, and you should consider it or something similar if you are debugging SNES without source code.

I also think transcript-style debugging is something we as an industry should consider more for debugging object code without source code. The benefit of source-style assembly debugging really only shines when you have symbolic debugging, or corresponding source code.

Using transcripts liberates you where you're not burdened with mapping control flows back to source code, there is only a series of behaviors. You could map them back to code, eventually. It's just not where you start.

Practical justification: I used transcripts to get these done

  • Ripping all maps of Lagoon
  • Enlarging the hitboxes in Lagoon
  • Making an NHL '94 player name, profile and stats editor
  • Making an NHL '94 player graphics decompression tool that's 100% accurate to the game's
  • Fixed a bug in Lord of the Rings
  • Disabling collisions in Lord of the Rings
  • Make plants in Harvest Moon be automatically watered

Bonus: Adding transcripts to C256 Foenix IDE debugger

C256 Foenix is a modern WDC 65816-based computer with an emulator.

For personal convenience I added transcript-style debugging to it, looks like this:

See there's duplicated instructions for a loop, and register output. With source-style, the listing looks like this, which provides a lot less information:

This transcript support is kept side-by-side with the default source-style debugger so that you can switch between them.

Enable it by going to "Settings" and checking the box for "Transcript-style debugger". When the box isn't checked, you get the default source-style debugger. The checkbox setting is remembered like the other settings so you don't need to check it every time.

I've already got some good use out of it. If you want to try it out, it's pushed to this private fork:

https://github.com/clandrew/FoenixIDE/tree/transcript

This change was not accepted for main because it seems like no one else uses this type of debugger, but the private fork is there for my purposes and if you want to use it too.

December 14th, 2022 at 7:21 am | Comments & Trackbacks (0) | Permalink
📌One of the next big things

📅December 2nd, 2022

Within some professional circles I'm constantly in this double bind in terms of how to talk about VR.

If I don't invest in it I'm out of touch with real gaming scenarios, too 'casual' to acknowledge high-end configs, pandering to the lowest common hardware denominator, no optimism or imagination for what high-end PC gaming looks like in the future.

If I do invest in it I'm frivolous, all about motion controls, all about Wiimotes, EyeToy and XBOX Kinect, out of touch with traditional gaming, rejecting of keyboard and mouse gaming as stodgy, trying to replace everyone's CoD with Dance Central.

I have to fight so hard for any kind of middle ground, or nuanced position, in ways that I haven't had to for LDA or 3D stereo. Where I believe in the technology, I buy products of the technology, at the same time I don't expect a future where it's as ubiquitous as the smartphone or internet browser and that's OK. I'm not big into VR but I have a positive opinion of it and there's a place for VR to live alongside traditional setups. The huge checks being written today around metaverse-type products consumed in VR are feeding into this and creating polarization, it stresses me out a lot sometimes.

December 2nd, 2022 at 5:41 am | Comments & Trackbacks (0) | Permalink
📌Register Spaces

📅September 20th, 2022

Recently someone asked me 'what are HLSL register spaces'? in the context of D3D12. I'm crossposting the answer here in case you also want to know.

A good comparison is C++ namespaces. Obviously, in C++, you can put everything in the default (global) namespace if you want, but having a namespace gives you a different dimension in naming things. You can have two symbols with the same name, and there's some extra syntax you use to help the compiler dis-ambiguate.

HLSL register spaces are like that. Ordinarily, defining two variables to the same register like this:

cbuffer MyVar : register(b0)
{
	matrix projection;
};

cbuffer MyVar2 : register(b0)
{
	matrix projection2;
};

will produce a compiler error, like

1>FXC : error : resource MyVar at register 0 overlaps with resource MyVar2 at register 0, space 0

But if you put them in different register spaces, like this:

cbuffer MyVar : register(b0, space0)
{
	matrix projection;
};

cbuffer MyVar2 : register(b0, space1)
{
	matrix projection2;
};

then it’s fine, it's not a conflict anymore.

When you create a binding that goes with the shader register, that’s when you can dis-ambiguate which one you mean:

              CD3DX12_DESCRIPTOR_RANGE range;
              CD3DX12_ROOT_PARAMETER parameter;

              UINT myRegisterSpace = 1;
              range.Init(D3D12_DESCRIPTOR_RANGE_TYPE_CBV, 1, 0, myRegisterSpace);
              parameter.InitAsDescriptorTable(1, &range, D3D12_SHADER_VISIBILITY_VERTEX);

Q: In the above example, what if I defined both MyVar and MyVar2 as b0, then assigned bindings to both of them (e.g., with SetGraphicsRootDescriptorTable)?

A: That's fine. Just make sure the root parameter is set up to use the register space you intended on.

Small, simple test applications all written by one person usually don’t have a problem with overlapping shader registers.

But things get more complicated when you have different software modules working together. You might have some other component you don’t own, which has its own shaders, and those shaders want to bind variables which occupy shader registers t0-t3. And then there’s a different component you don’t own, which also want t0-t3. Ordinarily, that’d be a conflict you can’t resolve. With register spaces, each component can use a different register space (still a change to their shader code, but a way simpler one) and then there’s no conflict. When you go to create bindings for those shader variables, you just specify which register space you mean.

Another case where register spaces can come in handy is if your application is taking advantage of bindless shader semantics. One way of doing that is: in your HLSL you declare a gigantic resource array. It could be unbounded, or have a very large size. Then at execution time, you populate and use bindings at various indices in the array. Ordinarily, two giant resource arrays would likely overlap each other and create a collision. With register spaces, there's no collision.

Going forward, you might be less inclined to need register spaces with bindless semantics. Why? Because with Shader Model 6.6 dynamic resource indexing, bindless semantics is a lot more convenient- you don't have to declare a giant array. Read more about dynamic resource indexing here: https://microsoft.github.io/DirectX-Specs/d3d/HLSL_SM_6_6_DynamicResources.html

Finally, register spaces can make it easier to port code using previous versions of the Direct3D programming API (e.g., Direct3D 11). In previous versions, applications could use the same shader register to mean different things for different pipeline stages, for example, VS versus PS. In Direct3D 12, a root signature unifies all graphics pipeline bindings and is common to all stages. When porting shader code, therefore, you might choose to use one register space per shader stage, to keep everything correct and non-ambiguous.

If you want some more reference material on register spaces, here's the section of the public spec:
https://microsoft.github.io/DirectX-Specs/d3d/ResourceBinding.html#note-about-register-space

September 20th, 2022 at 1:10 am | Comments & Trackbacks (0) | Permalink
📌Lord of the Rings SNES collisions

📅August 19th, 2022

Short version: To disable collisions e.g., walk through walls in J. R. R. Tolkien's Lord of the Rings for SNES, use the following Pro Action Replay codes

80E0C780 (Disable horizontal collisions)
80E13480 (Disable vertical collisions)

Longer explanation below.

There are some areas in maps I wanted to look at in this game, and those areas are inaccessible playing the game normally. How can you look at inaccessible parts of the game?

One option: rip the map. That would work, although it's cumbersome. It would cascade into the problem of also ripping the tileset graphics and figuring out how the each map datum maps to which tile. I did this process once for a different game, Lagoon. Those maps are here. It was doable because I already did some other projects involving that game so I had some information about it. For games I'm less familiar with, like LotR, it will take longer, probably so long it's not worth it.

An easier option instead is to disable collisions. So I set out to do that.

The general sense I had was that this will be a code change to the collision logic in the game. Some code must take the player's position, do some comparisons on it, and permit you to move or not move based on the comparisons. But which code is doing this?

1. Where position is stored

Breaking the problem down, the first step is to find where your position is stored in memory. It's likely to be an X, Y position since what kind of a maniac would store it in polar.

So there's a number, somewhere in the program. Classic problem where we don't know where it is stored. But worse yet, we also don't know what the number is, what its value is.

When faced with this kind of problem I do something I'm calling "special diffing", you can call it whatever you want, basically you take 3 or more memory dumps.

  • For dump 0, you've got your character somewhere.
  • For dump 1, you move them a little bit to the right.
  • For dump 2, you move them a little bit more to the right.

And then write some code that opens the dumps, looking through each offset for some number that's increasing from dump 0 to 1, and 1 to 2. Want more confidence? Take more memory dumps to have more data points.

Why move horizontal and not vertical? Because there isn't a strong convention in computer graphics about whether up is positive or not. For horizontal there's a pretty strong convention.

Why move to the right, and not left? Convenience, we probably expect the position value to increase going to the right.

Why move just a little, and not a lot? So that you don't overflow the byte type (e.g., exceed 255) since that's a hassle to account for.

Using this diffing technique gave a few answers

  • 7E05D3
  • 7E0AE7
  • 7E0EF7
  • 7E1087
  • 7E128F <-- The answer
  • 7EFD46

It was a low enough number to rule out the false positives and find the answer: 

7E128F

The other values corresponded to position too, but they were an output of it not an input. E.g., changing the value wouldn't stick, except for 7E128F.

2. What position is used for

The next obvious step is to break-on-write of position. We expect it to get hit whenever your character walks around, since it would get updated then. And moreover, we'd expect that code path to not get taken if you're hitting a wall.

Bad news here. The break-on-write will always fire regardless of whether you're moving or not-- the code is set up to always overwrite your position even if it doesn't need to. So that kind of breakpoint won't directly tell us which code paths fire or don't fire based on your hitting a wall.

For the record, it hits here:

$80/C88E 99 8F 12    STA $128F,y[$80:128F]   A:0100 X:0000 Y:0000 P:envmxdizc

That's okay. It will at least tell us something, when your position does get updated while moving, and we can still reason about what happens when it doesn't get updated.

And in particular, we can locally disassemble or CPU log to find the preceding operations

...

$80/C883 69 00 00    ADC #$0000              A:0000 X:0000 Y:0000 P:envmxdiZc
$80/C886 99 97 14    STA $1497,y[$80:1497]   A:0000 X:0000 Y:0000 P:envmxdiZc
$80/C889 AA          TAX                     A:0000 X:0000 Y:0000 P:envmxdiZc
$80/C88A 18          CLC                     A:0000 X:0000 Y:0000 P:envmxdiZc
$80/C88B 79 8F 12    ADC $128F,y[$80:128F]   A:0000 X:0000 Y:0000 P:envmxdiZc
$80/C88E 99 8F 12    STA $128F,y[$80:128F]   A:013A X:0000 Y:0000 P:envmxdizc

So some position-increment value gets saved to $80:1497, then increment the position by that number too. We can use this to work backwards and see a bunch of other fields updated as well.

Now we know the neighborhood of the collision code and can reason about the code path involved.

3. Finding the branch

There are a couple ways to proceed from here. There's a 'nice' option and a 'cheesy' option.

The 'nice' option is to take where we know the position is stored, and find the chain of operations done to its value. This works out if the control flow for controlling position is pretty localized-- say, if collision-checking and position-updating is all in one tidy function and they're right next to each other.

Unfortunately, the position-updating logic was messy. It was seemingly tangled up with the logic for checking for interact-ables (e.g., doors, NPCs). So while the 'nice' option is still an option, it's costly. Therefore there's the 'cheesy' option.

The cheesy option is to break on position change, using the information we found above, so we at least have some kind of frame delimiter and something to look for. Then enable CPU logging. Log:

  • one 'frame' where you can move, and
  • one 'frame' where you're obstructed.

Then strip out IRQs (they create noise) in the CPU log. So now we have a clean logfile.

What is a CPU log?

Just text.

And you know what you can do with text?

Put it through a differ.

So I put the result through a giant diff. For this I used Meld.

The diff isn't so crazy.

See there's data-divergence up until a certain point. After that, execution-divergence. It was a kind of thing where I scrolled through it and it caught my attention, so not a really thorough debugging experience, anyway the previous stuff to untangle where position is stored helped to understand the data-divergence and filter out noise in the diff.

And that ended up being the answer. The comparison

$80/E0C4 DD 41 E6    CMP $E641,x[$80:E643]   A:0010 X:0002 Y:00B2 P:envMxdizc
$80/E0C7 90 05       BCC $05    [$E0CE]      A:0010 X:0002 Y:00B2 P:envMxdiZC

will check if you're about to collide with a wall, or not. If you're free to move, you take the branch. If you're obstructed, you fall through. Therefore we can disable collisions by always taking the branch. So change

$80/E0C7 90 05       BCC $05    [$E0CE]

to

$80/E0C7 80 05       BRA $05    [$E0CE]

A quick test will show you this only covers horizontal collisions. Vertical goes down a completely separate code path. I guessed that they shared a common subroutine

$80/E0BD 20 22 D0    JSR $D022  [$80:D022]   A:00B2 X:0150 Y:00B2 P:envmxdizC

and this ended up being true. Setting a breakpoint on D022 ended up hitting for the vertical case:

$80/D022 DA          PHX                     A:0E05 X:016B Y:0095 P:envmxdizc
$80/D023 5A          PHY                     A:0E05 X:016B Y:0095 P:envmxdizc
$80/D024 8A          TXA                     A:0E05 X:016B Y:0095 P:envmxdizc
$80/D025 4A          LSR A                   A:016B X:016B Y:0095 P:envmxdizc
$80/D026 4A          LSR A                   A:00B5 X:016B Y:0095 
...
$80/D033 7A          PLY                     A:0000 X:0016 Y:026C P:envmxdiZc
$80/D034 FA          PLX                     A:0000 X:0016 Y:0095 P:envmxdizc
$80/D035 60          RTS                     A:0000 X:016B Y:0095 P:envmxdizc
$80/E12D E2 20       SEP #$20                A:0000 X:016B Y:0095 P:envmxdizc

at which point it's easy to step out 1 frame and see the caller. And it turns out the caller looks very similar to the horizontal case, with the same kind of branch. It has

$80/E131 D9 41 E6    CMP $E641,y[$80:E643]   A:0000 X:003F Y:0002 P:envMxdizc
$80/E134 90 05       BCC $05    [$E13B]      A:0000 X:003F Y:0002 P:eNvMxdizc

So you can do a similar thing, changing the branch on carry clear to a branch unconditional

$80/E134 80 05       BRA $05    [$E13B]

Putting it all together, the two codes are

80E0C780 (Disable horizontal collisions)
80E13480 (Disable vertical collisions)

Here's a demo of it in action, successfully getting past a door.

Side thing, I also used the code to get above the door in Bree. That said, even when enabling collisions again, it didn't take me anywhere. So the door's either controlled by non-'physical' means or not implemented.

I was still left with this question of whether we can conclusively say the door is not implemented.

It's one thing to prove a positive, prove a program does something. Easy enough, you show it doing the thing.

It's another thing to prove a negative, to prove a computer program will never do a thing. Can you prove the door can never open? Not ever? You can't really, you can only reach levels of confidence. Can you prove White Hand is not in Pokemon? Can you prove Herobrine is not in Minecraft? Has anyone ever conclusively proven that the pendant in Dark Souls doesn't do anything? Well, see, they ran the program through a simulator and-- just kidding, they went low tech and asked the director, so then it's a social engineering problem of whether you believe him.

When people use formal or other methods to prove program behaviors or nonbehaviors, they exploit constraints in the programming language or execution environment. For example, a language like Haskell has a rich set of constraints which are helpful in proving behavior. Or if a computer is unplugged and has no battery, you have confidence it won't power on. But in our case we're talking about object code, not source code, and we're talking about something the hardware could do. The instruction set of the object code alone doesn't provide helpful constraints. Hell, we can't even universally statically disassemble programs on this platform (because the choice of instruction width is dynamically chosen). Statically prove nonbehavior?

I'm not trying to give credibility to conspiracy theories or the mindset behind that kind of thinking. I'm trying to explain why you might not find a conclusive answer when you might want one. Anyway, through this exercise I got a greater level of confidence that the door doesn't go anywhere.

Some details

  • You can use both codes or one at a time.
  • Disabling collisions means you also can't interact with objects like doors. If you want to pass through doors, re-enable collisions or enable them for one direction.
  • If collisions are disabled for you, they're also disabled for allies, NPCs, and enemies.
  • Disabling collisions will let you pass through 'physical' doors in the game, where you're obstructed simply by where you're allowed to walk. For example, the gate in Moria, and the fires on the steps by the Balrog. There can be other 'non-physical' doors, where you need to trigger the right game event (e.g., have a key) to open them.

I used password tricks to get to the end area with all events signaled in any case, and had collisions off. I got to freely walk around the area where you find Galadriel with the mirror.

It turns out, the area is an infinite plane!

It's for the best not to try and rip the level data. /j

August 19th, 2022 at 6:19 am | Comments & Trackbacks (0) | Permalink
📌Why doesn't BTNS_DROPDOWN work?

📅May 17th, 2022

Say you're writing a Win32 application. You add a toolbar. Simple enough. Toolbar would look better with some things on it.

You want to, say, add a button to it. Like this

Flip through Petzold.

No chapters for toolbar dropdowns.

No obvious samples to use.

We're on our own, then.

Attempt 1: BTNS_DROPDOWN

You follow some of the sample code, and do the most natural thing. Use the toolbar button style 'BTNS_DROPDOWN'. (By the way, BTNS_DROPDOWN is the updated define for TBSTYLE_DROPDOWN. They mean the same thing.)


    TBBUTTON tbButtons[] =
    {
        { STD_CUT, 0, TBSTATE_ENABLED, BTNS_DROPDOWN, {0}, 0, (INT_PTR)L"Test" },
    };

    m_hwnd = CreateToolbarEx(
        parent,
        WS_CHILD | WS_VISIBLE | CCS_ADJUSTABLE | TBSTYLE_TOOLTIPS,
        0, 
        sizeof(tbButtons) / sizeof(TBBUTTON), //nBitmaps
        HINST_COMMCTRL,
        0, // wBMID
        tbButtons, //lpButtons
        sizeof(tbButtons) / sizeof(TBBUTTON), // iNumButtons
        90, 90, 90, 90,
        sizeof(TBBUTTON)); // uStructSize

    SetWindowLongPtr(m_hwnd, GWLP_USERDATA, (LONG_PTR)this);
    SendMessage(m_hwnd, TB_AUTOSIZE, 0, 0);
    ShowWindow(m_hwnd, TRUE);

Compile and run. STD_CUT is your standard built-in Windows scissors 'cut' icon. Result looks like this:

That visually looks fine. But wait. Let's try clicking on it.

Clicking on it doesn't do anything 🙁

It doesn't even show a 'button is pushed' animation. It should at least do that, right?

What gives? It's not disabled.

Attempt 2: TBSTYLE_EX_DRAWDDARROWS

Okay, so maybe our initialization of the dropdown menu was incomplete. Dropdown menus usually have an arrow at the right. Perhaps we need to add the "arrow at the right" extended style? Let's try adding the code

    SendMessage(m_hwnd, TB_SETEXTENDEDSTYLE, 0, TBSTYLE_EX_DRAWDDARROWS);

So that now, it looks like


    TBBUTTON tbButtons[] =
    {
        { STD_CUT, 0, TBSTATE_ENABLED, BTNS_DROPDOWN, {0}, 0, (INT_PTR)L"Test" },
    };

    m_hwnd = CreateToolbarEx(
        parent,
        WS_CHILD | WS_VISIBLE | CCS_ADJUSTABLE | TBSTYLE_TOOLTIPS,
        0, 
        sizeof(tbButtons) / sizeof(TBBUTTON), //nBitmaps
        HINST_COMMCTRL,
        0, // wBMID
        tbButtons, //lpButtons
        sizeof(tbButtons) / sizeof(TBBUTTON), // iNumButtons
        90, 90, 90, 90,
        sizeof(TBBUTTON)); // uStructSize

    SendMessage(m_hwnd, TB_SETEXTENDEDSTYLE, 0, TBSTYLE_EX_DRAWDDARROWS);

    SetWindowLongPtr(m_hwnd, GWLP_USERDATA, (LONG_PTR)this);
    SendMessage(m_hwnd, TB_AUTOSIZE, 0, 0);
    ShowWindow(m_hwnd, TRUE);

Let's compile and run it and see what it looks like now.

This looks better. There's an arrow on the right. That should mean something good. Let's try clicking on it.

Clicking on the button itself works.

Clicking on the arrow doesn't 🙁

Attempt 3: BTNS_WHOLEDROPDOWN

Maybe the ticket is WHOLEDROPDOWN. Looking it up in the header, BTNS_WHOLEDROPDOWN purports to

That sounds like it could make the whole button appear responsive, so why not let's try it.

Result looks like this:

The arrow is all merged with the button.

Okay. What if we try to click on it?

Nothing happens 🙁

What to do?

The Answer

The answer: toolbar dropdown menus, by default, don't have any animation for clicking on them. They're not like normal buttons. That's right, the button is still working, there's just no visual feedback unless you explicitly attach some yourself.

To make the toolbar dropdown button do something, you have to just trust that it is set up ok, and attach some behavior to the dropdown notification.

Fortunately you don't have to re-invent the wheel to do that. Here's an easy way to attach a simple pop-up menu to the dropdown.

First, you need to have your WndProc pay attention to WM_NOTIFY. The handler can be something like


    case WM_NOTIFY:
    {
        LPNMTOOLBAR lpnmtb = (LPNMTOOLBAR)lParam;

        if (lpnmtb->hdr.code == TBN_DROPDOWN)
        {
            // Get the coordinates of the button.
            RECT rc;
            SendMessage(lpnmtb->hdr.hwndFrom, TB_GETRECT, (WPARAM)lpnmtb->iItem, (LPARAM)&rc);

            // Convert to screen coordinates.            
            MapWindowPoints(lpnmtb->hdr.hwndFrom, HWND_DESKTOP, (LPPOINT)&rc, 2);

            HMENU hMenuLoaded = LoadMenu(g_hInst, MAKEINTRESOURCE(IDR_MENU1));

            // Get the submenu for the first menu item.
            HMENU hPopupMenu = GetSubMenu(hMenuLoaded, 0);

            TPMPARAMS tpm;
            tpm.cbSize = sizeof(TPMPARAMS);
            tpm.rcExclude = rc;

            TrackPopupMenuEx(hPopupMenu, TPM_LEFTALIGN | TPM_LEFTBUTTON | TPM_VERTICAL, rc.left, rc.bottom, hWnd, &tpm);

            DestroyMenu(hMenuLoaded);
        }
        break;
    }

As for the menu IDR_MENU1, you can point it to a menu you have defined. Or, if you want a placeholder thing, put something like this in your .rc file:

IDR_MENU1 MENU
BEGIN
    POPUP "TEST"
    BEGIN
        MENUITEM "Option 1",                        ID_TEST_OPTION1
        MENUITEM "Option 2",                        ID_TEST_OPTION2
    END
END

That goes along with these defines in the Resources.h coupled to the .rc file:

#define IDR_MENU1                       132
#define ID_TEST_OPTION1                 32777
#define ID_TEST_OPTION2                 32778

Build, and you get this:

In animated form:

The dropdown works. Success!

It so happens if you re-try Attempt 2, TBSTYLE_EX_DRAWDDARROWS with a pop up menu, then it'll provide visual arrow-is-pressed feedback where it didn't before. See:

This is because BTNS_DROPDOWN, TBSTYLE_EX_DRAWDDARROWS, and BTNS_WHOLEDROPDOWN follow a common principle: anything that appeared unresponsive with no pop up menu attached is responsive once a menu is attached.

This system was not super well explained elsewhere, so maybe this will help you.

May 17th, 2022 at 3:17 am | Comments & Trackbacks (0) | Permalink
📌Extension

📅April 25th, 2022

I made a Visual Studio extension for 65C816 syntax highlighting. Suitable for SNES or C256 Foenix projects. Looks like this:

The source+binary are on GitHub, here: https://github.com/clandrew/vscolorize65c816

I had some past experience working on a big existing system in a Visual Studio extension in a job I had a little while ago. This was my first time writing an extension for a recent version from scratch. The experience was different.

I accomplished what I set out to do and it's working well, but the path of getting there was cumbersome.

Here is a list of the problems I ran into.

Problem: No extension template.

Root cause: Template requires an optional add-on.

How debugged: search engine.

Problem: Official template has build error right out of the gate:
error VSSDK1048: Error trying to read the VSIX manifest file "obj\Debug\extension.vsixmanifest". Could not load file or assembly 'Microsoft.VisualStudio.Threading, Version=16.7.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a' or one of its dependencies. The system cannot find the file specified.

Root cause: The template has a missing dependency. To fix, you have to update the NuGet package "Microsoft.VSSDK.BuildTools".

How debugged: Shotgun debugging

Build error
How to fix: right click project, go to NuGet Package Manager, and update Microsoft.VSSDK.BuildTools

Problem: Template does not behave correctly out of the gate. When launched with debugger, it is never loaded

Root cause: The template is missing an attribute

How debugged: Search engine

Add the highlighted lines to fix

You don't create a syntax highlighter object out of the blue. You define a 'Package' object to set it up. I defined one in code.

Problem: Package object is never instantiated.

Root cause: You have to define, at a minimum, two attributes to make it get loaded: [PackageRegistration] and [ProvideAutoLoad].

How debugged: Looking at other extensions as examples + shotgun debugging

Add something like the highlighted lines or else the package won't get instantiated.

Problem: The package is instantiated, but doesn't correctly associate with the intended files. Error message when opening files that have ProvideLanguageExtension. "An error occured in 'file' when attempting to open 'file.s'. There is no editor available for 'file.s'. Make sure the application for the file type (.s) is installed."

Root cause: Something is stale. Reload the file! Even if you restart the whole IDE, it's not enough! It stays stale unless you specifically reload the file

How debugged: Shotgun debugging

Problem: The package adds a LanguageInfo service, but the LanguageInfo is never instantiated.

Root cause: You have to call AddService after InitializeAsync, not before

How debugged: Shotgun debugging + code examples

It should be ordered like this.

Problem: The syntax is not highlighted as intended

Root cause: Need to have IVsColorizer::ColorizeLine return the intended values

How debugged: Actual debugging

Problem: The choice of which attribute value maps to which color seems arbitrary

Root cause: There is a system of default colors. You can know that default through experimentation, or over-ride it in a specific way

How debugged: Experimentation

Takeaway- I accomplished what I was trying to do, but there was a lot of shotgun debugging and 'just trying things'. The extension framework has you hook into a complicated system which is also closed-off and opaque, so there is no way to directly debug it.

It may as well be running on a different computer.

By "system", I'm referring to

  • The mechanism that instantiates your custom package and calls InitializeAsync on it
  • The thing that looks at your custom package and loads it based on PackageRegistration
  • The thing that sets up associations using package attributes like ProvideLanguageExtension.
  • The thing that executes methods of objects set up with IServiceContainer::AddService

Look at my extension or other people's samples. You're supposed to define a **** ton of attributes on the Package class.

Here's an example from an open source project on GitHub:

^attributes above the class definition.

It's to the point where the attributes are really a language in and of themselves. Guess what, they feed into some complicated loader that executes before your code is ever executed. If there's a mistake in the attributes? Get your psychic powers ready. Because there's no insight into this closed system or way see what it's doing. It doesn't even have the decency to put its state to debug console.

The time I spent actually debugging problems was in the minority. Most problems, the only way to fix them was by trying things. It's really bad. They could not be debugged in the debugger because they occur in a complicated system you don't have access to. This system and its higher-level concepts were not documented well enough to automatically know what to type. "Is ProvideLanguageService not supposed to have languageResourceID 100? Is that the reason it's failing, or something else?"

I'm not even angry about the 17KB of code and god knows how much memory it takes to make text a different color according to a simple scheme. What's really bad is this this closed off system that everyone is supposed to just be okay with, since I see it as part of a trend. UI layouts from markup are like this. App store launching is like this. Software junk food "press F5"-style emulators and VMs are like this. As we get more and more complicated software systems, there isn't enough follow-through to make them fully open and debuggable. So if they 'just work the first time' fantastic. But we all live in reality. Things will go wrong, and when they do, it's clear the system is grand and complicated and undocumented and undiagnosable.

As a random example, can you imagine if Direct3D 12 had no debug layer, and all it told you was E_INVALIDARG? Why would we accept this more broadly?

This is why I keep writing GUI applications as executables with Win32 or Windows Forms say. The form designer has the decency to give you a call stack. Actionable stack or some error string should be the bare minimum.

Shifting topics, here are things I learned about Visual Studio custom colorizers:

  • The 'state' values passed to/from your callbacks have whatever meaning you want them to. The meaning of states is all user-defined. It's opaque to Visual Studio.
  • An IVsLanguageInfo is reponsible for providing two things: a colorizer, and a code window manager. But you don't need to have both. You can just provide one if you want. For example you can provide a colorizer, but return E_NOTIMPL to IVsLanguageInfo::GetCodeWindowManager.
  • In IVsColorizer::ColorizeLine, character at index N in the 'pszText' corresponds to element N of 'attributes' parameter.
  • To add colors to text, you set values in the 'attributes' parameter of IVsColorizer::ColorizeLine. Like this:

Why does 1 mean red? Because it's based on whatever you set in your IVsProvideColorableItems callback object.

Yes, it's 1-indexed.

If you don't have an IVsProvideColorableItems set up, you'll get some defaults with blue, green, red, and black (default) text numbered in some way. You can experiment what means what. Using a value of greater than 6 will crash the extension, so that's fun. In my case, the default was almost good enough, but I wanted gray for directives like C++ has, for e.g., #include and #pragma. So I did end up implementing IVsProvideColorableItems.

All told, if you use the syntax highlighter with custom build tools, it looks like this:

so the experience is pretty smooth.

Direct download to the release is here https://github.com/clandrew/vscolorize65c816/releases/tag/v1.0.

April 25th, 2022 at 4:12 am | Comments & Trackbacks (0) | Permalink
📌Artificial or not

📅April 15th, 2022

I had a conversation with someone recently.

It went like

Them: … And that's for someday whenever we have AI.
Me: We have AI. We had it for over 30 years
Them: I mean real AI.
Me: People keep raising the goalposts on what counts as AI.
Them: Well, fundamentally AI is whenever a computer makes a decision, so I'm referring to something more than that.
Me: A decision. A branch?

What is a decision made by a computer?

Consider say train tracks. You know, where there's a switch on the train track to choose which side the train goes onto. Say the switch is to the left, so the train goes to the left.

Would you say that the train track "made a decision"? Probably not. The track hardware was configured a certain way, so the train went that way. Makes sense. Easy to explain. To say the train track "made a decision" is giving this really simple hardware a lot of credit. If you were to say the train tracks "make a decision", you'd be saying all inanimate objects in your life are making decisions all the time- like a house of cards makes a 'decision' to stay up, or a building makes a 'decision' to stay standing-- it would all sound a bit crazy and the word "decision" would be so broad that it loses all meaning.

Now, adjust the scenario. Say there's more trains, more tracks. Three trains, ten tracks. More switches. Again the trains go according to the switches. Would you then say that the train tracks "made a decision"? Again, probably not. Although the trains' paths were more complicated, they can still be explained. The switches controlled where the trains were going to go. You can see how they work.

Now, adjust the scenario further. There's a billion trains on a billion tracks. Yes, that's a lot of trains. The paths are so complicated we only have insight into some of the switches. We can only debug some parts of the system directly. That said, we do have a model for the rest of the system. There are real trains and tracks. The model has an explanation based on hardware and not magic.

A computer system is this way like trains on a track. It doesn't make sense to say that a computer "makes a decision" any more than a train track does. There is electricity flowing through different paths, and although these paths are complicated they can be explained and expressed as functions.

You can go a step further and claim that human brains are the same. More trains, more tracks compared to computers- more complication. Yet, if you have belief in the natural world, you can buy an explanation where it's all running on hardware and not magic. The difference between the human brain and the train tracks isn't anything fundamental. The difference is the complexity of the system.

Why is a train track just "some hardware configuration" while human's behavior gets elevated to this higher status, gets this special label called "a decision"? It's the complexity and that's all. A system that's sufficiently complicated and hard to simulate gets the elevated status of "decision". Nothing's inherently special about a "decision" other than the fact we've decided it's too complicated to reason about.

People ascribe magical qualities to systems that are complicated. "Free will". "Agency". "Decision". They're all functions, they all have a set of inputs and outputs. Yet these words have this mysterious quality about them, like they happen independently, spontaneously, defying explanation. I say the spontenaity is all an illusion. With enough information, any decision made by human or computers can be debugged and stepped through. If we had a system with infinite computing power and perfect information, we could predict the future, even if it means simulating forward.

This is why free will is a comforting illusion. We're living in that moment where a coin has been flipped, yet the answer has not been revealed to you yet.

This is in regards to things at macroscopic scale. Not quantum particles

You might be saying, "I don't like this idea. I like free will. Because what does it matter? Whether the coin's been flipped and not yet revealed yet, or not flipped at all-- you have the same information. It doesn't change anything."

Or you're saying, "I don't like this idea. I like free will. Because, if people think they don't have free will, it makes them feel helpless and lethargic, like they shouldn't take initiative on things."

Those are both the wrong takeaway, though. Just because free will is an illusion, doesn't mean the things you do don't matter. They do matter. And as for the coin flip, does it change anything- well, no and yes.

If you believe the coin flip is a function with inputs (physical world) and output (a heads or tails), then you might want to debug and more deeply understand how the inputs affect the result. You might look into physics simulations. How does air resistance affect the coin's path in the air? What about the weight distribution of coins? How does your style of coin-flipping affect its travel through the air? You can learn something about why you got a heads or tails.

On the other hand if you believe the coin flip is 100% purely decided in the moment, based on completely undeterminable factors, your inquiry about it stops there. The result is just random. It may as well be magic. It just is.

Mapping the idea of the "coin flip" onto human decisions, the real takeaway is that human decisions can be explained. They have a physical, natural basis. They're not random. They're not magic. Yes, they are super complicated- they're functions with lots of inputs and outputs- they are functions nonetheless. People have reasons for the things they do.

I don't care whether you believe in "free will". I don't care whether you buy my idea about free will being an illusion, about decisions and "the coin flip" or not. If you don't, that's fine.

I do care that you accept human decisions can be explained. They're not really spontaneous, not unexplainable black boxes. They're a product of previous work and exposure to the outside world. From whatever starting point, that's the end point to end up at. I understand a lot of decisions are hard to explain. But we can try and we should.

The idea of explainable decisions may seem like an obvious no-brainer. The thing is, I keep running into people for whom it's not obvious. They will say things of the form, "Red-haired people don't like baseball". Arguments of the form "X type of people don't like to do Y". In some cases, the person has even written essays on it, read studies on it, and spent dozens and dozens of hours debating with others on podcasts about it.

But when you press them on the $64,000 question, "Why do red-haired people not like baseball", it's not even that they don't have an answer- they will get bewildered by the question like they've never even considered it before. Their answer is "they just don't." Okay. That's it, they just don't. Just 'cause. They don't.

Could be these people believe in bio-essentialism. Like red hair intrinsically, genetically causes you to like certain sports and not others. It's determined from birth. Maybe even earlier. No matter how you're socialized, who raises you, they'll claim your involvement in baseball in really affected by red hair. Or at least, there's a very severe natural ceiling in redhead interest. Bio-essentialiasm has become un-pallateable over the years, especially when used to describe gender or racial groups, and is not well scientifically explained or justified (compared to heritability, which is different), so they don't want to say that out loud.

Could be they are confused about descriptive claims. Descriptive claims are things like "the house is red.", it's what something is today. By contrast, normative claims are "the house should be green", it's about what we should do, what we ought to do. Sometimes, people see a descriptive claim like "red-haired people don't tend to like baseball", that will get confused into a normative claim, "red-haired people should not get into baseball". It's as if things today represent the 'correct' state of the world and it's a lost cause to try and change anything, ignoring the fact things have changed before and are constantly changing.

Could be they don't care about the reason. They want to talk about the correlation they're seeing, where it would appear red-haired people don't currently play baseball, but stop short of trying to debug why. This might seem incredible, given how much time and energy they've spent on the topic. All those hours spent debating with people, listening to podcasts, making social media posts, editing videos. Still it can happen. Our educational system has a lot of gaps where people end up having a deep lack of curiosity.

If unchallenged directly on debugging the reason, there's a typical pattern that comes up. They will dance around the subject, make descriptive claims that imply bio-essentialism, gesture towards inexplicable "choices" of red-haired people, and use those to funnel into normative claims.

For example, they'll say something of the form, "Studies show that currently, only 5% of red-haired people like baseball, much lower than average. That's inarguable. And those are the choices they're making, nothing wrong with that. So you shouldn't put red-haired people on baseball teams so they're not going to be invested in the sport anyway".

What happened here? Dissecting this, they took a descriptive claim about how things are today. They used "inarguable" to subtly imply a lack of bias around interpretation of the information, plus a way to use speaking in absolutes to imply the description will always hold. Then used the claim to make a judgment about what we should do, along with the word "choices" to say it's a just state of the world. Where to question it would be to take power away from red-haired people somehow, even when that's what the very proposal is doing. Although it is sneaky it falls apart when challenged directly, since there's no well-justified reason for the claim, even if it sounds like there is one.

The confusion, the lack of curiosity, it comes from this idea that people invest heavily in the concept of opaque human "decisions". As if humans aren't this huge network of train tracks, a billion tracks with different switches, as if instead they're built on randomness and magic. People use "decisions" and "free will" as a cop-out from having to investigate any more. It keeps them from having to ask the hard questions of why someone might do something, or what would motivate something to happen. They can write it off as "that's their decision", "just because that's what they wanted to do", without acknowledging that people don't do random things. The indiscriminate acceptance of "just because" leads to poorly-formed normative claims, and people putting the trappings of thoughtfulness around bad arguments.

Although we can not debug every neuron in the brain, we can intuitively know that people don't do random things.

Imagine your favorite hobby, or a sport you like to play. If you were air-dropped in the middle of the forest or desert and raised there apart from civilization, where would you get the idea to do that hobby? How would you ever think to kick a black-and-white ball around? How would you think to slide a rubber disc on ice? The idea came from other people. Or, can you accept the premise that advertising works? It does, doesn't it? That makes more sense than companies spending billions of dollars on literally nothing, something that doesn't work. People keep getting exposed to advertisements, so they are more likely to buy that product. It's hard to accept how shaped you are by your environment but that's the bitter medicine everyone needs to accept.

Although human motives are complicated, it doesn't mean we shouldn't even try to understand them. Human intelligence and artificial intelligence might have different levels of complexity, but that's all. They are both based on natural causes, not randomness.

If your computer program has some misbehavior and it was important to you, you'd output some logs, you'd attach a debugger. You wouldn't say, "that's the computer's decision" and refrain from investigating any more.

April 15th, 2022 at 2:38 pm | Comments & Trackbacks (0) | Permalink
📌Literally Unreachable

📅April 12th, 2022

Here is some C++:

compiled to x86.

Obvious disclaimer this is brittle, very platform and compiler dependent, will break if you look at it the wrong way.

How it works: this part

    if (fnChar[0] == 0xE9) // Strip off dummy call
    {
        realMain = fnChar + ((fnChar[2] << 8) | fnChar[1]) + 5;
    }

is because some compiler settings can mean your functions are called from jump thunks. For example, if you take the address of function "main", stored as fnChar, it gives you

Rather than the function body you'd expect, it's an entry in a sea of jumps. These are incremental linking jump thunks. While we could deal with this by disabling incremental linking, it's not too hard to robustify against. To look up what's the "real" address of main, the code looks at the offset of the jump-relative, adds it on plus 5 which is the length of the jmp operation.

After that is this part:

    for (int i = 0; i < INT_MAX; ++i) // Find offset to jump to
    {
        if (realMain[i + 0] == 0xCC && realMain[i + 1] == 0x68)
        {
            return reinterpret_cast<SimpleFn>(realMain + i + 1);
        }
    }

This seeks through main for some delimiter. The delimiter, in this case, is

Man, this is a garbage post. 0/10 effort

Wherever it finds the int 3 delimiter, that's the code we want to call. Could key off of only 0xCC but that's a very common term, it also happens to be used for setting up an argument to __CheckForDebuggerJustMyCode, so use the first byte of the subsequent push to dis-ambiguate.

And finally, the 

exit(0);

is a cheesy trick to compensate for the fact that we didn't set up the stack frame properly. We'd run into this problem when jumping into the middle of almost any function (by messing with the function pointer). As far as the compiler's concerned, you're supposed to jump to the beginning of functions. By jumping into the middle, we skip a bunch of initialization, like the allocation of stack-allocated variables in function scope. And switching to global variables doesn't help for debug. When compiling for debug, the generated code allocates stack space automatically for you even if you have no local variables.

When main exits, it'll compare the stack pointer, and make sure it reflects base pointer + stack allocation to make sure nothing corrupted the value of the stack pointer somehow. This validation would catch a legitimate issue in this case. Bailing out with exit avoids the whole thing.

In all, this is a case where the compiler says you have code that's not reachable but it actually is.

The principle of this being possible is obvious to some people, but not all. I've had people say to me that "good compilers can always 100% statically know if code is reachable or not". It's not true, for C++ to x86 anyway. I tell them, "No, code is just code. At the end of the day, if code exists in a binary, you can execute it. Compilers can't exhaustively evaluate what generated code will do. They can't solve the halting problem" They don't understand what I mean and there's a gap in understanding so I hope a proof-by-example would explain, even if it's a super contrived and impractical one.

"But what if I enable optimizations?" If you enable optimizations, the code labeled "unreachable" will be actually missing from the binary. Yes that means the compiler is wrong. To work around I'd suggest adding some dummy control flow to tell the compiler the code is reachable.

This was tested using MSVC.

If you want to try the above code, here:

https://godbolt.org/z/saW4KnKqE

April 12th, 2022 at 8:09 am | Comments & Trackbacks (0) | Permalink
📌Is SetPixel still slow?

📅March 1st, 2022

Answer: mostly, yes. Explanation below.

Part 1: Yes or No

Remember GDI? Say you're using GDI and Win32, and you want to draw some graphics to a window. What to do. You read the documentation and see what looks like the most obvious thing: "SetPixel". Sounds good. Takes an x and y and a color. What more could you want? Super easy to use.

But then, you see a bunch of cautionary notes. "It's slow." "It's inefficient." "Don't do it."

Don't do it?

Well. All these cautionary notes you see are from days of yore:

  • Computers are faster now. Both CPU and GPU. Take an early CS algorithms class, experiment with solutions. You’ll see sometimes the biggest optimization you can do is to get a faster computer.
  • An earlier Windows graphics driver model. Say, XPDM not WDDM. WDDM means all hardware-accelerated graphics communicate through a “Direct3D-centric driver model”, and yes that includes GDI. Changes in driver model can impose changes in performance characteristics.
  • Different Windows presentation model. That's something this API is set up to negotiate with, so it could affect performance too. Nowadays you're probably using DWM. DWM was introduced with Windows Vista.

The date stamps give you skepticism. Is that old advice still true?

As a personal aside, I've definitely seen performance advice from people on dev forums that is super outdated and people get mis-led into following it anyway. For example for writing C++ code, to "manually turn your giant switch case into a jump table". I see jump tables in my generated code after compilation... The advice was outdated because of how much compilers have improved. I've noticed a tendency to trust performance advice "just in case", without testing to see if it matters.

Let us run some tests to see if SetPixel is still slow.

I wrote a benchmark program to compare

  • SetPixel, plotting each pixel of a window sequentially one by one, against
  • SetDIBits, where all pixels of a window are set from memory at once.

In each case the target is a top-level window, comparing like sizes. Each mode effectively clears the window. The window is cleared to a different color each time, so you have some confidence it’s actually working.

Timing uses good old QPC. For the sizes of timespans involved, it was not necessary to get something more accurate. The timed interval includes all the GDI commands needed to see the clear on the target, so for SetDIBits that includes one extra BitBlt from a memory bitmap to the target to keep things fair.

The source code of this benchmark is here.

Here are the results

Width Height Pixel Count SetPixel SetDIBits
1000 1000 1000000 4.96194 0.0048658
950 950 902500 4.7488 0.0042761
900 900 810000 4.22436 0.0038637
850 850 722500 3.71547 0.0034435
800 800 640000 3.34327 0.0030824
750 750 562500 2.92991 0.0026711
700 700 490000 2.56865 0.0023415
650 650 422500 2.21742 0.0022196
600 600 360000 1.83416 0.0017374
550 550 302500 1.57133 0.0015125
500 500 250000 1.29894 0.001311
450 450 202500 1.05838 0.0010062
400 400 160000 0.826351 0.0009907
350 350 122500 0.641522 0.0006527
300 300 90000 0.467687 0.0004657
250 250 62500 0.327808 0.0003364
200 200 40000 0.21523 0.0002422
150 150 22500 0.118702 0.0001515
100 100 10000 0.0542065 9.37E-05
75 75 5625 0.0315026 0.000122
50 50 2500 0.0143235 6.17E-05

Viewed as a graph:

Conclusion: yeah, SetDIBits is still way faster than SetPixel in general, in all cases.

For small numbers of pixels, the difference doesn't matter as much. For setting lots of pixels, the difference is a lot.

I tested this on an Intel Core i7-10700K, with {NVIDIA GeForce 1070 and WARP} with all similar results.

So the old advice is still true. Don't use SetPixel, especially if you’re setting a lot of pixels. Use something else like SetDIBits instead.

Part 2: Why

My benchmark told me that it’s still slow, but the next question I had was ‘why’. I took a closer look and did some more thinking about why it could be.

It's not one reason. There's multiple reasons.

1. There's no DDI for SetPixel.

You can take a look through the public documentation for display devices interfaces, and see what’s there. Or, take a stab at it and use the Windows Driver Kit and the provided documentation to write a display driver yourself. You’ll see what’s there. You’ll see various things. You’ll see various blit-related functions in winddi.h. For example, DrvBitBlt:

BOOL DrvBitBlt(
  [in, out]      SURFOBJ  *psoTrg,
  [in, optional] SURFOBJ  *psoSrc,
  [in, optional] SURFOBJ  *psoMask,
  [in]           CLIPOBJ  *pco,
  [in, optional] XLATEOBJ *pxlo,
  [in]           RECTL    *prclTrg,
  [in, optional] POINTL   *pptlSrc,
  [in, optional] POINTL   *pptlMask,
  [in, optional] BRUSHOBJ *pbo,
  [in, optional] POINTL   *pptlBrush,
  [in]           ROP4     rop4
);

That said, you may also notice what’s not there. In particular, there’s no DDI for SetPixel. Nothing simple like that, which takes an x, y, and color. It’s important to relate this to the diagrams on the “Graphics APIs in Windows” article, which shows that GDI talks to the driver for both XPDM and WDDM. It shows that every time you call SetPixel, then what the driver sees is actually far richer than that. It would get told about a brush, a mask, a clip. It’s easy to imagine a cost to formulating all of those, since they you don’t specify them at the API level and the API is structured so they can be arbitrary.

2. Cost of talking to the presentation model

There’s a maybe-interesting experiment you can do. Write a Win32 application with your usual WM_PAINT handler. Run the application. Hide the window behind other windows, then reveal it once again. Does your paint handler get called? To reveal the newly-revealed area? No, normally it doesn’t.

So what that must logically mean is that Windows kept some kind of buffer, or copy of your window contents somewhere. Seems like a good idea if you think about it. Would you really want moving windows around to be executing everyone’s paint handlers all the time, including yours? Probably not. It’s the good old perf-memory tradeoff in favor of perf, and it seems worth it.

Given that you’re drawing to an intermediate buffer, then there’s still an extra step needed in copying this intermediate buffer to the final target. Which parts should be copied, and when? It seems wasteful to be copying everything all the time. To know what needs to get re-copied, logically there has to be some notion of an “update” region, or a “dirty” region.

If you’re an application, you might even want to aggressively optimize and only paint the update region. Can you do that? At least at one point, yes you could. The update region gets communicated  to the application through WM_PAINT- see the article “Redrawing in the Update Region”. There’s a code example of clipping accordingly. Now, when I tried things out in my application I noticed that PAINTSTRUCT::rcPaint is always the full window, even in response to a small region invalidated with InvalidateRect, but the idea is at least formalized in the API there.

Still, there’s a cost to dealing with update regions. If you change one pixel, that one-pixel area is part of the update region. Change the pixel next to it, the region needs to be updated again. And so on. Could we have gotten away with having a bigger, coarser update region? Maybe. You just never know that at the time.

If you had some way of pre-declaring which regions of the window you’re going to change, (e.g., through a different API like BitBlt), then you wouldn’t have this problem.

3. Advancements in the presentation model help, but not enough

In Windows, there is DWM- the Desktop Window Manager. This went out with Windows Vista and brought about all kinds of performance improvements and opportunity for visual enhancements.

Like the documentation says, DWM makes it possible to remove level of indirection (copying) when drawing contents of Windows.

But it doesn’t negate the fact that there still is tracking of update regions, and all the costs associated with that.

4. Advancements in driver model help, but not enough

DWM and Direct3D, as components that talk to the driver through the 3D stack, have a notion of “frames” and a particular time at which work is “flushed” to the GPU device.

By contrast, GDI doesn’t have the concept of “frames” or flushing anything. Closest thing would be the release of the GDI device context, but that’s not strictly treated as a sign to flush. You can see it yourself in how your Win32 GDI applications are structured. You draw in response to WM_PAINT. Yes there is EndPaint, but EndPaint doesn’t flush your stuff. Try it if you want- comment out EndPaint. I tried it just to check and everything still works without it.

Since there isn’t a strict notion of “flushing to the device”, SetPixel pixels have to be dispatched basically immediately rather than batched up.

5. 3D acceleration helps, but not enough

Nowadays, GDI blits are indeed 3D accelerated.

I noticed this firsthand, too. Very lazy way to check- in the “Performance” tab in Task manager when I was testing my application, I saw little blips in the 3D queue. These coincided with activity in the SetPixel micro-benchmark.

Again, very lazy check. Good to know we are still accelerating these 2D blits, even as the graphics stack has advanced to a point of making 3D graphics a first-class citizen. Hardware acceleration is great for a lot of things, like copying large amounts of memory around at once, applying compression or decompression, or manipulating data in other ways that lend itself to data-parallelism.

Unfortunately, literally none of that helps this scenario. Parallelism? How? At a given time, the driver doesn’t know if you’re done plotting or what you will plot next or where. And it can’t buffer up the operations and execute them together, because it, like Windows, doesn’t know when you’re done. Maybe, it could use some heuristic.

But that brings this to the punchline: even if the driver had psychic powers, it could see into the future and know exactly what the application is going to do and did an absolutely perfect job of coalescing neighboring blits together, it doesn’t negate any of the above costs, especially 1. and 2.

Conclusion

Even in the current year, don’t use SetPixel for more than a handful of pixels. There’s reasons to believe the sources of the bottlenecks to have changed over 30 years, yet even still the result is the same. It’s slow and the old advice is still true.

Epilogue: some fantasy world

This post was about how things are. But, what could be? What would it take for SetPixel not to be slow? The most tempting way to think about this is to flatten or punch holes through the software stack. That works, even if it feels like a cop-out.

March 1st, 2022 at 5:04 am | Comments & Trackbacks (0) | Permalink
📌Grind--

📅February 19th, 2022

To make it so you don't need to water your plants in Harvest Moon for Super Nintendo, use the PAR codes

82A8ACEA
82A8ADEA

Explanation below.

The game 'Harvest Moon' for Super Nintendo has fun elements, but also repetitive ones. One of them that wore on me was having to water your plants. If you water at night, it's not even a skill-based action mechanic since you can restore your energy and night lasts forever. I wanted to experience the game and see its content, but not have the repetitive action of watering.

Idea: patch the game so that watering is not needed

First approach was to take memory dumps before and after watering a tile, and diff them. Seems ok. But, the diffs were too noisy and I didn't know what I was looking for. How were the farm tiles stored? Was it even one byte per tile, one byte per pair of tiles, or something else entirely? I didn't even know that part yet, so I gave up on it.

Instead, I tried something way dumber- keep watering a tile with a view of live memory open, and watch for changes. I had an idea of what the storage could be- one byte per tile, arranged sequentially, so I looked for that. And I planted some test plants in an observable pattern. This plus exploiting timing of changes made it way easier to discern signal from noise and I found it.

There were not one, but two places the tile data lived. For the tile I'm standing near, the first was at 7E1100 and that one I found first. When I left the farm and came back I saw that the data got wiped and restored, so that meant it's a cache and not the primary copy.

Looking for a dupe of it in memory, I found that at 7EAC30, more likely to be the primary copy.

From experimenting I found this out about the tile storage:

  • It is one byte per tile
  • Tiles are stored sequentially. Nothing too crazy.

And as for what tile value means what thing, I found

Tile ValueWhat It Means
0x00Untilled, unwatered ground
0x01Untilled, unwatered ground (different graphic from above)
0x07Tilled, unwatered ground
0x08Tilled, watered ground
0x58Unwatered potato seed
0x59Watered potato seed
0x68Unwatered turnip seed
0x69Watered turnip seed

(Not exhaustive.)

From the data points there are, watering a tile simply increments its value by 1. So when it rains, something must iterate through all the tiles and increment their value by 1.

To find out what that is, I set a break-on-write of 0x7EAC32, the location of the top-left plant, looking for the value to change from 0x58 to 0x59. This took me right into this code

(Paste below is multiple debugging transcripts spliced together so don't put too much stock in the reg values.)

void ProcessWeather()
...
$82/8390 8F 1E 1F 7F STA $7F1F1E[$7F:1F1E]   A:0400 X:0400 Y:0400 P:eNvMxdizc
$82/8394 22 D6 89 82 JSL $8289D6[$82:89D6]   A:0400 X:0400 Y:0400 P:eNvMxdizc

// Call UpdateFarmTiles, transcribed below
$82/8398 22 11 A8 82 JSL $82A811[$82:A811]   A:0400 X:0400 Y:0400 P:eNvMxdizc

$82/839C 22 09 82 82 JSL $828209[$82:8209]   A:0400 X:0400 Y:0400 P:eNvMxdizc
...


void UpdateFarmTiles() - $82/A811
// Preconditions:
//    Weather is stored at $7E0196. 0x0 means sunny, 0x2 means rainy.
//    Farm data is stored around $7EAC30.
// This function is called when you sleep, no matter the weather or if you save.

$82/A811 E2 20       SEP #$20                A:0007 X:000E Y:0002 P:envmxdizC
$82/A813 C2 10       REP #$10                A:0007 X:000E Y:0002 P:envMxdizC
$82/A815 A9 04       LDA #$04                A:0007 X:000E Y:0002 P:envMxdizC
$82/A817 8D 81 01    STA $0181  [$00:0181]   A:0004 X:000E Y:0002 P:envMxdizC
$82/A81A C2 20       REP #$20                A:0004 X:000E Y:0002 P:envMxdizC
$82/A81C A0 00 00    LDY #$0000              A:0004 X:000E Y:0002 P:envmxdizC
$82/A81F A2 00 00    LDX #$0000              A:01E0 X:0400 Y:01E0 P:eNvmxdizc

StartProcessingTile:
$82/A822 5A          PHY                     A:00D0 X:00D0 Y:01D0 P:eNvmxdizc
$82/A823 DA          PHX                     A:00D0 X:00D0 Y:01D0 P:eNvmxdizc
$82/A824 86 82       STX $82    [$00:0082]   A:00D0 X:00D0 Y:01D0 P:eNvmxdizc
$82/A826 84 84       STY $84    [$00:0084]   A:00D0 X:00D0 Y:01D0 P:eNvmxdizc
$82/A828 20 3C B1    JSR $B13C  [$82:B13C]   A:00D0 X:00D0 Y:01D0 P:eNvmxdizc
$82/A82B E2 20       SEP #$20                A:074D X:074D Y:01D0 P:envmxdizc

// Load the state for a tile in your farm. We look at just 1 byte
$82/A82D BF E6 A4 7E LDA $7EA4E6,x[$7E:AC33] A:074D X:074D Y:01D0 P:envMxdizc 

; Do various things for the different tile types.
$82/A831 D0 03       BNE $03    [$A836]      A:0758 X:074D Y:01D0 P:envMxdizc
$82/A836 C9 03       CMP #$03                A:0758 X:074D Y:01D0 P:envMxdizc
$82/A838 B0 03       BCS $03    [$A83D]      A:0758 X:074D Y:01D0 P:envMxdizC
$82/A83A 4C 1B A9    JMP $A91B  [$82:A91B]   A:0701 X:074F Y:01D0 P:eNvMxdizc
$82/A83D C9 A0       CMP #$A0                A:0758 X:074D Y:01D0 P:envMxdizC
$82/A83F 90 03       BCC $03    [$A844]      A:0758 X:074D Y:01D0 P:eNvMxdizc
$82/A844 C9 06       CMP #$06                A:0758 X:074D Y:01D0 P:eNvMxdizc
$82/A846 D0 03       BNE $03    [$A84B]      A:0758 X:074D Y:01D0 P:envMxdizC
$82/A84B C9 07       CMP #$07                A:0758 X:074D Y:01D0 P:envMxdizC ; Is tilled soil?
$82/A84D F0 55       BEQ $55    [$A8A4]      A:0758 X:074D Y:01D0 P:envMxdizC
$82/A84F C9 08       CMP #$08                A:0758 X:074D Y:01D0 P:envMxdizC
$82/A851 D0 03       BNE $03    [$A856]      A:0758 X:074D Y:01D0 P:envMxdizC
$82/A856 C9 1E       CMP #$1E                A:0758 X:074D Y:01D0 P:envMxdizC
$82/A858 F0 4A       BEQ $4A    [$A8A4]      A:0758 X:074D Y:01D0 P:envMxdizC
$82/A85A C9 1F       CMP #$1F                A:0758 X:074D Y:01D0 P:envMxdizC
$82/A85C D0 03       BNE $03    [$A861]      A:0758 X:074D Y:01D0 P:envMxdizC
$82/A861 C9 1D       CMP #$1D                A:0758 X:074D Y:01D0 P:envMxdizC
$82/A863 D0 03       BNE $03    [$A868]      A:0758 X:074D Y:01D0 P:envMxdizC
$82/A868 C9 20       CMP #$20                A:0758 X:074D Y:01D0 P:envMxdizC
$82/A86A B0 03       BCS $03    [$A86F]      A:0758 X:074D Y:01D0 P:envMxdizC
$82/A86F C9 39       CMP #$39                A:0758 X:074D Y:01D0 P:envMxdizC
$82/A871 D0 03       BNE $03    [$A876]      A:0758 X:074D Y:01D0 P:envMxdizC
$82/A876 C9 53       CMP #$53                A:0758 X:074D Y:01D0 P:envMxdizC
$82/A878 D0 03       BNE $03    [$A87D]      A:0758 X:074D Y:01D0 P:envMxdizC
$82/A87D C9 61       CMP #$61                A:0758 X:074D Y:01D0 P:envMxdizC
$82/A87F D0 03       BNE $03    [$A884]      A:0758 X:074D Y:01D0 P:eNvMxdizc
$82/A884 C9 6F       CMP #$6F                A:0758 X:074D Y:01D0 P:eNvMxdizc
$82/A886 D0 03       BNE $03    [$A88B]      A:0758 X:074D Y:01D0 P:eNvMxdizc
$82/A88B C9 79       CMP #$79                A:0758 X:074D Y:01D0 P:eNvMxdizc
$82/A88D D0 03       BNE $03    [$A892]      A:0758 X:074D Y:01D0 P:eNvMxdizc
$82/A892 C9 7C       CMP #$7C                A:0758 X:074D Y:01D0 P:eNvMxdizc
$82/A894 D0 03       BNE $03    [$A899]      A:0758 X:074D Y:01D0 P:eNvMxdizc
$82/A899 C9 70       CMP #$70                A:0758 X:074D Y:01D0 P:eNvMxdizc
$82/A89B B0 69       BCS $69    [$A906]      A:0758 X:074D Y:01D0 P:eNvMxdizc

$82/A89D 29 01       AND #$01                A:0758 X:074D Y:01D0 P:eNvMxdizc	; Mask 
$82/A89F F0 03       BEQ $03    [$A8A4]      A:0700 X:074D Y:01D0 P:envMxdiZc
...

$82/A8A4 C2 20       REP #$20                A:0700 X:074D Y:01D0 P:envMxdiZc

$82/A8A6 AD 96 01    LDA $0196  [$00:0196]   A:0700 X:074D Y:01D0 P:envmxdiZc	; Load weather
										; 0x0 means sunny.
										; 0x2 means rainy.

$82/A8A9 29 02 00    AND #$0002              A:0002 X:074D Y:01D0 P:envmxdizc

; If not rainy, skip ahead--
$82/A8AC F0 03       BEQ $03    [$A8B1]      A:0002 X:074D Y:01D0 P:envmxdizc	

; If it is rainy, goto IncrementTileValue to mark the tile as watered.					
$82/A8AE 4C 06 A9    JMP $A906  [$82:A906]   A:0002 X:074D Y:01D0 P:envmxdizc
...

IncrementTileValue:
; This is a common path for all kinds of tile incrementing, it's not just for rain.

$82/A906 E2 20       SEP #$20                A:0002 X:074D Y:01D0 P:envmxdizc
; Load early-out cond
$82/A908 AF 19 1F 7F LDA $7F1F19[$7F:1F19]   A:0002 X:074D Y:01D0 P:envMxdizc	
$82/A90C C9 03       CMP #$03                A:0000 X:074D Y:01D0 P:envMxdiZc	; 
$82/A90E F0 59       BEQ $59    [$A969]      A:0000 X:074D Y:01D0 P:eNvMxdizc	;

; Load tile value
$82/A910 BF E6 A4 7E LDA $7EA4E6,x[$7E:AC33] A:0000 X:074D Y:01D0 P:eNvMxdizc	

; Apply 'watered' status
$82/A914 1A          INC A                   A:0058 X:074D Y:01D0 P:envMxdizc	

WriteRainEffect:
; X=0x74C means just to the right of shipping bin.
; Value of 0x59 means 'watered'.
$82/A915 9F E6 A4 7E STA $7EA4E6,x[$7E:AC32] A:0059 X:074C Y:01D0 P:envMxdizc											
		
; Goto DoneProcessingTile.								
$82/A919 80 4E       BRA $4E    [$A969]      A:0059 X:074C Y:01D0 P:envMxdizc	
...

OnUntilledSoil:
$82/A91B E2 20       SEP #$20                A:0701 X:074F Y:01D0 P:eNvMxdizc
$82/A91D AF 19 1F 7F LDA $7F1F19[$7F:1F19]   A:0701 X:074F Y:01D0 P:eNvMxdizc
$82/A921 C9 02       CMP #$02                A:0700 X:074F Y:01D0 P:envMxdiZc
$82/A923 F0 44       BEQ $44    [$A969]      A:0700 X:074F Y:01D0 P:eNvMxdizc
$82/A925 C9 03       CMP #$03                A:0700 X:074F Y:01D0 P:eNvMxdizc
$82/A927 F0 40       BEQ $40    [$A969]      A:0700 X:074F Y:01D0 P:eNvMxdizc
$82/A929 AF 1B 1F 7F LDA $7F1F1B[$7F:1F1B]   A:0700 X:074F Y:01D0 P:eNvMxdizc
$82/A92D 29 03       AND #$03                A:0706 X:074F Y:01D0 P:envMxdizc
$82/A92F D0 38       BNE $38    [$A969]      A:0702 X:074F Y:01D0 P:envMxdizc	; Goto DoneProcessingTile
...

DoneProcessingTile:
$82/A969 C2 30       REP #$30                A:0059 X:074C Y:01D0 P:envMxdizc
$82/A96B FA          PLX                     A:0059 X:074C Y:01D0 P:envmxdizc
$82/A96C 7A          PLY                     A:0059 X:00C0 Y:01D0 P:envmxdizc
$82/A96D 8A          TXA                     A:0059 X:00C0 Y:01D0 P:envmxdizc
$82/A96E 18          CLC                     A:00C0 X:00C0 Y:01D0 P:envmxdizc
$82/A96F 69 10 00    ADC #$0010              A:00C0 X:00C0 Y:01D0 P:envmxdizc
$82/A972 AA          TAX                     A:00D0 X:00C0 Y:01D0 P:envmxdizc
$82/A973 E0 00 04    CPX #$0400              A:00D0 X:00D0 Y:01D0 P:envmxdizc
$82/A976 F0 03       BEQ $03    [$A97B]      A:00D0 X:00D0 Y:01D0 P:eNvmxdizc
$82/A978 4C 22 A8    JMP $A822  [$82:A822]   A:00D0 X:00D0 Y:01D0 P:eNvmxdizc

DoneProcessingField:
$82/A97B 98          TYA                     A:0400 X:0400 Y:01D0 P:envmxdiZC
$82/A97C 18          CLC                     A:01D0 X:0400 Y:01D0 P:envmxdizC
$82/A97D 69 10 00    ADC #$0010              A:01D0 X:0400 Y:01D0 P:envmxdizc
$82/A980 A8          TAY                     A:01E0 X:0400 Y:01D0 P:envmxdizc
$82/A981 C0 00 04    CPY #$0400              A:01E0 X:0400 Y:01E0 P:envmxdizc
$82/A984 F0 03       BEQ $03    [$A989]      A:01E0 X:0400 Y:01E0 P:eNvmxdizc
$82/A986 4C 1F A8    JMP $A81F  [$82:A81F]   A:01E0 X:0400 Y:01E0 P:eNvmxdizc
...

This provides enough information to understand how the 'watered' status gets applied. So to apply watered status irrespective of rain, you can just change the branch below

$82/A8A9 29 02 00    AND #$0002              A:0002 X:074D Y:01D0 P:envmxdizc

; If not rainy, skip ahead--
$82/A8AC F0 03       BEQ $03    [$A8B1]      A:0002 X:074D Y:01D0 P:envmxdizc	

; If it is rainy, goto IncrementTileValue to mark the tile as watered.					
$82/A8AE 4C 06 A9    JMP $A906  [$82:A906]   A:0002 X:074D Y:01D0 P:envmxdizc

to no ops. In other words, change 

82A8AC: F0
82A8AD: 03

to

82A8AC: EA
82A8AD: EA

Expressing this as a PAR code, it looks like

82A8ACEA
82A8ADEA

See a demo of the change

It's a bit more fun this way. Enjoy

February 19th, 2022 at 5:29 am | Comments & Trackbacks (0) | Permalink
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