[Linux] Alpha is broken in DDS files when packed with DXT

rkfg

The story is simple, I wanted to try a new crosshair, namely "Wilson's White Dot + Skie's Hit Indicator Crosshair" by @Mendasp‌, and it looked nice. But when I shoot something or someone, the red version of the crosshair was displayed with an ugly semitransparent black square around it.


I liked the mod and this was annoying so I decided to dig into the issue. The stock crosshairs work fine, there must be something different with the modded ones. I used the "file" command to get some info about them.
Stock:

crosshairs.dds: Microsoft DirectDraw Surface (DDS), 64 x 1024, 
crosshairs-hit.dds: Microsoft DirectDraw Surface (DDS), 64 x 1024, 

Modded:

crosshairs.dds: Microsoft DirectDraw Surface (DDS), 64 x 1024, 
crosshairs-hit.dds: Microsoft DirectDraw Surface (DDS), 64 x 1024, DXT1

Aha! And that was it. I installed a gimp-dds package, opened the crosshairs-hit.dds file and saved it without the DXT1 compression. Now it works as expected, clear and nice. But of course this should work out of the box without any manipulations, I tried another crosshair mod months ago and it had even the normal crosshair with a completely opaque black square around it. Now I can guess it had DXT1 compression for the main file, not only for the hit.

Mendasp

As the mod name says, I took two mods and repackaged them, but I can resave as DXT5 (which all ui textures are meant to use) and republish, thanks for letting me know.

GhoulofGSG9

DXT1 doesn't support a alpha channel and therfore generates smaller files than DXT5. So yeah DXT1 was the issue

More about DXT can be found at Wikipedia: http://en.wikipedia.org/wiki/S3_Texture_Compression

BTW 268 will include a new version of nvcompress which is alot faster and works also at pcs without cuda installed.

Also the overall rule for dds files in ns2 is:

Has alpha channel? -> use DXT5
Has no alpha channel? -> use DXT1

DC_Darkling

so basicly the mod sucked...

rkfg

Mendasp wrote: »

As the mod name says, I took two mods and repackaged them, but I can resave as DXT5 (which all ui textures are meant to use) and republish, thanks for letting me know.

Does it mean that you don't experience the described issue? That's interesting because

GhoulofGSG9 wrote: »

DXT1 doesn't support a alpha channel and therfore generates smaller files than DXT5. So yeah DXT1 was the issue

...if it doesn't support alpha channel then why GIMP opens it with alpha enabled and lets it be resaved with it properly? I mean, if there was no alpha, the background should be black or white but it was absolutely transparent. I couldn't find the difference until I file'd all those files. If you don't have black boxes with DXT1-compressed textures, it can only mean that DXT1 is handled differently on Windows OR the Direct3D version of the engine versus the OpenGL one. Maybe blending shaders differ? It's pretty simple to blend the crosshair texture so that black is transparent, it's called additive blending I suppose.

Mendasp

Updated. I guess I need to update a few more crosshair mods I have out there that used this combination.

Jaito

http://cgit.freedesktop.org/~mareko/libtxc_dxtn/

And, ejecute in command line with:
force_s3tc_enable=true [your gl_program]

or:
export force_s3tc_enable=true