Strange texture filtering problem

[Nevander]

Engine used: GZDoom 2.2.0

I just noticed that if you set a texture filtering mode (most likely only the mipmap ones), after a while it degrades the textures to a point where you can see "lines" or a "grain." I don't know what is causing it but I do know if I start a level with a filter mode of none (linear mipmap) and play the level for a while, then return to an area it will do this. Changing to another filter mode then changing back instantly fixes it and "re-draws" the filtered textures. Is this normal or is my GPU/CPU a piece of crud and isn't processing the textures correctly?

To see what I'm talking about, consider this image below. On the left side you see a corridor of E2M2 and notice how it looks like there are horizontal streaks in the textures (both the floor and walls). This is with a filter mode of none (linear mipmap) but it was taken after being across the map for a while and returning to this place. On the right side it is the exact same wall and floor, but switched to another filter mode and right back at the same moment and then screenshot taken without moving around the map any more. Changing the mode seems to "reset" the textures or something and redraw them correctly.

[Graf Zahl]

. Is this normal or is my GPU/CPU a piece of crud and isn't processing the textures correctly?

What GPU do you have?

[Nevander]

GPU: PowerColor AMD Radeon R9 270X
CPU: Intel Core i7-4820K 3.7 GHz

EDIT: Through more experimentation it seems the anisotropic filter is the problem not the filter mode, since it happened with none (trilinear) as well. If I set the filter mode to none with nearest or linear mipmap but with anisotropic filter set to none, I get the result on the left side. If I up the anisotropic filter it starts to smooth out. So apparently it's forgetting the anisotropic filter on textures that I've been around and left and came back to later or something since changing any option seems to refilter them.

[Graf Zahl]

Sounds like a driver bug. It's not the first for AMD and these days apparently everybody uses anisotropic filitering so they probably never noticed themselves...