BUG: gl_scaleskytextures 1 does not scale external 24-bit images

[hemostx]

ezQuake version:
3.6 with gl_scaleskytextures (is this new from 3.5?)

OS/device including version:
W10 20H2 GTX 1070 472.12
Should be irrelevant, quirk in texmode logic found

Describe the bug
With gl_scaleskytextures 1 gl_picmip/max_size only applies to 8-bit sky textures. 24-bit textures do not get scaled.

I noticed this while playing around with the gl_scale* cvars for documentation and could compare between i.e. dm3, which features skies that ezquake provides 24-bit external textures for, and skull which only has an 8-bit sky

To Reproduce
Steps to reproduce the behavior:
requires ezquake's 24-bit skies, ie with ezquake/base.pk3

1. gl_picmip 5;gl_scaleturbtextures 1;gl_scaleskytextures 1
2. start dm3 (has skies and turbs easily comparable in the same rooms), go to pent or LG
3. water gets scaled down, sky does not
4. gl_no24bit 1;vid_restart
5. water and sky get scaled down

Expected behavior
I would expect the 24-bit skies to get scaled down with gl_scaleskytextures 1, just like the 8bit versions, and as per gl_scaleturbtextures/gl_scalemodeltextures, which already existed in 3.2, for consistency.

Screenshots
With 8-bit textures

• gl_scaleskytextures 0
  
• gl_scaleskytextures 1
  

With 24-bit textures

• gl_scaleskytextures 0
  
• gl_scaleskytextures 1
  

Extra context

For an 8-bit texture, R_LoadBrushModelTextures calls R_InitSky, and this eventually calls R_Upload32 which does the downscaling of the texture.

For an external texture, R_LoadBrushModelTextures calls Mod_LoadExternalSkyTexturewhich always passes 0 instead of the texmode flags parameter for the solid texture (alpha texture gets the flag), but of course just changing it to pass flags to R_LoadTextureImageisn't enough. :)

It looks like Mod_LoadExternalSkyTexture always just sets a TEX_NOSCALE flag.

[hemostx]

I think I found what went wrong while comparing the slightly different paths taken through R_LoadBrushModelTextures for sky/turb/model textures.

I mentioned Mod_LoadExternalSkyTexture always just sets a TEX_NOSCALE flag.

• For gl_scaleturbtextures 0 flags are 34 (TEX_MIPMAP + TEX_NOSCALE)
• For gl_scaleturbtextures 1 flags are 2(TEX_MIPMAP)
• For gl_scaleskytextures 0 flags are 32 (TEX_NOSCALE)
• For gl_scaleskytextures 1 flags are 0 (nothing, which appears to behave like TEX_NOSCALE)

So I eventually changed Mod_LoadExternalSkyTexture to calculate flags as seen for turb/sky.

It also always passed 0 to R_LoadTextureImage for the solidskytexture flags, which I found out to behave like TEX_NOSCALE, while the alphatexture did get the flags passed to it, so I changed that as well.

That applied the scaling with gl_picmip.

After this I went to look for behaviour with gl_max_size and this was fine as well.

I saw R_LoadBrushModelTextures does special work for gl_miptextevel, so I was expecting more work to be needed on this patch. But it turns out in the next couple of lines, the general "miptexlevel does not apply to 24 bit textures" takes care of that, so all seems well on that front and no downscaling occurs as expected.