Not everything has to be drawn as a triangle. You can apply a fragment shader symmetrically to every pixel in a framebuffer, instead of using geometry to apply

Not everything has to be drawn as a triangle. You can apply a fragment shader symmetrically to every pixel in a framebuffer, instead of using geometry to apply different fragment shaders within each triangle. This technique is commonly used to post-process already-rendered scenes, like with a tone mapping shader or depth of field effects. But for simple scenes you can also put an entire rendering engine in the fragment shader, typically using ray marching. Here are some examples of this technique being used to draw voxels: https://www.shadertoy.com/results?query=voxel https://www.shadertoy.com/results?query=voxel