The first shader I ever wrote drew nothing at all

Automated excerpt

Two programs, two completely different jobs Every WebGL draw call runs two shader programs back to back, and they're not doing the same kind of work at all. The vertex shader runs once per vertex — a corner point of a triangle, since everything the GPU draws eventually decomposes into triangles. A fragment shader has no idea it's one of two million running this frame. It's perfect for a fragment shader, because a fragment shader is designed, on purpose, to never need to know what any other pixel is doing. A 1920×1080 frame is a little over two million pixels.

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