This is a quick project I submitted for a contest. Important to note that I'm not eligible to win the contest because I'm helping run it, but can submit things for fun.

Here's this one:

If you're really perceptive you may notice the resemblance to the Gordie Howe bridge.

The thing with shadertoy is you can't directly import any meshes or textures, everything needs to be specified in a fragment shader in screen space. So there is a bunch of geometry expressed as sort of screenspace fill tests. And the scene is organized to render foreground and background separately.

• For the bridges, there's a fill test for "does this overlap with the top of a diamond shape". To do that for a diamond shape at the origin, where its width and height are 1, it's simple, you just add X and Y and check that the sum is less than 1. Then you can adjust the formula where the diamond is squished (i.e., X and Y radius are different) and is adjusted to a location that's not the origin.
  • The only other interesting thing is there's some extra logic to add sort of a falloff to the edges so they look smooth and antialiased.
• For the clouds, there's a similar fill test for "does this overlap with an ellipse". Similarly, the fill test is simple for a circle at the origin of radius 1. And then you can work it out for a squished circle (i.e., an ellipse) where it's at a location that's not the origin.
• For the stars and plane (the red dot is an airplane), those are just simple aliased filled circles. They are small so it doesn't seem worthwhile to alias them. For some extra visual interest, the stars have kind of a twinkling effect.
• The plane travels back and forth based on a sine wave of the current time. This seems a bit more visually interesting than seeing a plane always travel in the same direction.
• The clouds are different colors and travel by taking modulus of time, so they always travel one direction, not back and forth. So do the cars. I think this makes the most sense.

To view this shader in Shadertoy, here it is: https://www.shadertoy.com/view/f3dGDj