3D Backgrounds for Touhou-like Bullet Hell Shmup

[slime]

Are you just saying that things like circles, rectangles and images will just have a third Z parameter?

No, but you can already reposition the Z coordinates (and even change the 3D rotation) of 2D primitives by using a vertex shader.

[raidho36]

Are you just saying that things like circles, rectangles and images will just have a third Z parameter?

If you use color blending, that automatically makes depth testing pointless. That's because you produce output color by blending rendered color with pre-existing color, and depth information gets ignored. How would it even make sense, if objects wouldn't show up behind transparent things?

Because of the way it works, depth testing can only be used to render solid polygons. But at that specific task, depth testing is an exceedingly handy tool.