Show HN: OpenGL in super slow motion – visualising Z-buffering

Of course, in practice the rasterization happens in terms of larger tiles that contain many 2x2 pixel quads, and many quads are shaded in parallel, with the shader executing in lockstep for all pixels simultaneously. But that's an optimization that can be ignored for exposition, unlike the 2x2 quads.

Z-buffer is a very clever way to draw shapes. The only other way used practically is ray-tracing, where you cast rays through pixels on the screen and see where they intersect with the surface. Z-buffer reverses it - instead of casting rays towards surface we project set points on the surface (vertices) onto the screen. Even though it's asymptotically O(n) vs ray tracing's O(log n), practically it's very fast. The vast majority of CG, from movies to video games relies on this algorithm and I don't know what could be more important. All the stuff listed in other comments: texture mapping, texture mapping, shaders, perspective projection etc are specific algorithms, which don't deal with the shape drawing directly and not used everywhere.

This is not directly exposed in any common API, although Vulkan's renderpasses are intended to help write applications that behave efficiently on tiling renderers (as this kind of GPU is often called).

This isn't exposed to the programmer directly (Vulkan's multi pass API is related) but it has performance characteristics that we engine programmers need to be aware of.