Some weird lines with CRN files

[illwieckz]

Reported on IRC today by @sweet235.

JPEG:

CRN:

I noticed it with other textures in the past, on my end the glitch changes with the distance.

The bug is there since years. I suspect a bug in the mipmapping code.

The mipmap images are already part of the CRN file. When I convert CRN to DDS with crunch (that I assume to only change the container, not recompress the file), and load the DDS in GIMP, I see no issue in the precomputed mip-map images. So I assume this is a bug in our renderer.

[VReaperV]

Forcing a specific mipmap level (no interpolation) might help identify the issue.

[slipher]

Using Forlorn's floor texture as my testbed, I tried the 0.52.1 engine with recent assets and the bug was there. But 0.52.1 engine with 0.52.1 assets does not have the bug. So this suggests the possibility of an asset pipeline bug.

It does seem to be specific to certain mip levels. Setting various values of r_picmip or r_imageMaxDimension resulted in either the lines going away, or becoming bigger (due to lower resolution).