Doing fun stuff strictly in a fragment shader: how to do perspective and draw meaningful scenes?

This question isn't as much about how to do stuff as it is about how to find existing tutorials on doing this stuff. I just can't seem to find the right search terms. I want to understand and do stuff like this: https://www.shadertoy.com/view/4ldGz4 Or this: https://www.shadertoy.com/view/4lsczM Is there a name for that? What techniques will I need? I understand that a fragment shader takes pixel coordinates and returns the color of that pixel. Basically, if I need to draw a 3D scene, I need to implement a basic 3D engine and a rasterizer - all in the fragment shader?