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Bug 2897

Summary: SDL reports it 'Can't find matching GLX visual' when requesting an sRGB capable framebuffer
Product: SDL Reporter: manwiuxas
Component: videoAssignee: Ryan C. Gordon <icculus>
Status: RESOLVED FIXED QA Contact: Sam Lantinga <slouken>
Severity: normal    
Priority: P2 Keywords: triage-2.0.4
Version: HG 2.1   
Hardware: x86_64   
OS: Linux   
Attachments: reproduction case

Description manwiuxas 2015-03-02 10:06:30 UTC 
I'm using Ubuntu Gnome 14.10, with Nvidia 550 TI and proprietary drivers.

Whenever I request SDL_GL_SetAttribute(SDL_GL_FRAMEBUFFER_SRGB_CAPABLE, 1), I get "Can't find matching GLX visual" message on trying to create the window.

Thing is, that I DO get an sRGB capable OpenGL framebuffer on the machine, even if I don't explicitly request it.

I've also tested it on Windows and got an sRGB framebuffer there regardless of the state of SDL_GL_FRAMEBUFFER_SRGB_CAPABLE flag.

This bug impairs creation of cross-platform projects that require sRGB for proper display of color.
Comment 1 Ryan C. Gordon 2015-03-04 06:09:12 UTC 
I remember hearing something about this. We'll look at this for 2.0.4.

--ryan.
Comment 2 Ryan C. Gordon 2015-04-06 01:14:42 UTC 
Created attachment 2106 [details]
reproduction case


This program fails to make a GL context on X11 with Nvidia's proprietary drivers (prints "(nil)") It works on Intel's open source drivers, at least on this machine (prints a valid pointer address for the GL context).

--ryan.
Comment 3 Ryan C. Gordon 2015-04-06 03:42:25 UTC 
Hmm, the Nvidia drivers don't like when you choose a visual with:

    attribs[i++] = GLX_FRAMEBUFFER_SRGB_CAPABLE_ARB;

...it instead wants...

    attribs[i++] = GLX_FRAMEBUFFER_SRGB_CAPABLE_ARB;
    attribs[i++] = True;

(which appears to be incorrect, according to the GLX specification.)

Mesa seems to allow this, though, so I guess we'll just force that True item for now.

--ryan.
Comment 4 Ryan C. Gordon 2015-04-06 04:08:04 UTC 
(In reply to Ryan C. Gordon from comment #3)
> Hmm, the Nvidia drivers don't like when you choose a visual with:
> 
>     attribs[i++] = GLX_FRAMEBUFFER_SRGB_CAPABLE_ARB;
> 
> ...it instead wants...
> 
>     attribs[i++] = GLX_FRAMEBUFFER_SRGB_CAPABLE_ARB;
>     attribs[i++] = True;
> 
> (which appears to be incorrect, according to the GLX specification.)

Uh, wait, Mesa wants the same thing, maybe it was just more forgiving about picking a visual, or some other cosmic force stepped in.

    http://cgit.freedesktop.org/mesa/mesa/tree/src/glx/glxext.c?id=5e59f895c468c1ac497ad925b8bddd7f227c89a2#n548

It's not clear to me where it says this attribute needs a "True" specified; other boolean items in the Mesa implementation don't do this (look for FETCH_OR_SET).

I'm confused. But at least the fix is easy now!

--ryan.
Comment 5 Ryan C. Gordon 2015-04-06 04:15:51 UTC 
Oh well, this should be fixed now in http://hg.libsdl.org/SDL/rev/f5b468964b0b

--ryan.