Shaders: How to draw high fidelity graphics with just x and y coordinates

You can do some pretty impressive things: https://shadertoy.com/

I skimmed it but didn't see any mention of "ray marching", which is raytracing done in a shader. GPUs are pretty fast now. You can just do that. However you do have to encode the scene geometry analytically in the shader - if you try to raytrace a big bag of triangles, it's still too slow. There's more info on this and other techniques at https://iquilezles.org/articles/