Texture glitches research (Patreon)

Here's a quick way to get rid of some texture glitches: Set d_mipcap to 1.

This fixes the glitched edges of liquid textures whose internal textures are not 64x64. I don't know why.

This also fixes a very specific case: E1M1, the animated texture of the second button in the dark room with light switches on a series of downward ramps above slime (the envirosuit room). When the mipmap level is zero (close to the camera), the animated red glowing texture of the button drifts horizontally following the player's position. I guess this doesn't happen on the other buttons because their textures are at other orthogonal angles in worldspace.

This E1M1 glitch may also be related to the severe glitch that used to plague liquids when I switched compilers to make Retroquad more compatible with modern platforms. I'll test this theory later.

Anyway, it's weird how those glitches doesn't happen in submips. It's not related to raw texture size, since it also happens with the internal textures, which are much smaller (8x smaller than the QRP textures, and 4x smaller than the textures of the "mankrip demo"). I'll keep looking for a proper fix.

[edit] Fixed the E1M1 button texture glitch.

Plus, I've found out yet another glitch that only happens in the water of the "mankrip demo" (this bug doesn't affect lava). When the player is away from the water surfaces, the right end of their polygon spans gets glitchy. Mipmap levels aren't related to this, as it doesn't disappear when zooming in. Only the actual depth affects it.

The liquids' turbulence is also misaligned on mipmap zero. But it's correct on all submips.

I'll work on the mipmap-related glitches before trying to figure out the depth-related glitch.