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Bug 5372 - GLES2 render backend uses wrong pixel format for textures
Summary: GLES2 render backend uses wrong pixel format for textures
Status: RESOLVED INVALID
Alias: None
Product: SDL
Classification: Unclassified
Component: render (show other bugs)
Version: 2.0.13
Hardware: x86_64 Linux
: P2 normal
Assignee: Ryan C. Gordon
QA Contact: Sam Lantinga
URL:
Keywords:
Depends on:
Blocks:
 
Reported: 2020-12-01 01:54 UTC by Ryan C. Gordon
Modified: 2020-12-10 06:07 UTC (History)
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Description Ryan C. Gordon 2020-12-01 01:54:09 UTC 
In GLES2_CreateTexture:

    switch (texture->format)
    {
    case SDL_PIXELFORMAT_ARGB8888:
    case SDL_PIXELFORMAT_ABGR8888:
    case SDL_PIXELFORMAT_RGB888:
    case SDL_PIXELFORMAT_BGR888:
        format = GL_RGBA;
        type = GL_UNSIGNED_BYTE;
        break;
    // ...

...this causes problems, though, if you created a texture with SDL_PIXELFORMAT_ABGR8888, since it will treat the data uploaded with SDL_UpdateTexture as RGBA instead of ABGR, swizzling the colors.

This might be a simple fix in SDL, but I have to check if there's a reason this was done (is only GL_RGBA is reliably available to GLES? etc).
Comment 1 Ryan C. Gordon 2020-12-01 02:40:13 UTC 
Turns out GLES doesn't support many texture formats, which is why these all get gated through GL_RGBA.

In GLES2_TexSubImage2D, we already create a temporary copy of the data to change its packing; instead, we can probably just use SDL_CreateRGBSurfaceFrom with the incoming pixels then use SDL's normal conversion routines to handle packing _and_ format adjustment, replacing the existing code outright.

--ryan.
Comment 2 Ryan C. Gordon 2020-12-01 08:44:17 UTC 
Wait, this might be an Emscripten or Firefox bug, it doesn't reproduce with the GLES2 renderer on X11, and upon closer inspection, SDL already converts pixels to a supported texture format for the render backend at a higher level before calling its UpdateTexture method.

Going to leave this open for now while I figure out what went wrong.

--ryan.
Comment 3 Ryan C. Gordon 2020-12-10 06:07:48 UTC 
Disregard, turns out the emscripten app was accidentally mangling pixel data before handing it to SDL, and SDL's renderer was processing the incorrect data correctly.

--ryan.