Can SDL create a sRGB OpenGL context?

Question

The documentation of SDL does not seem to mention much about color spaces. I don't see any SRGB flag/parameter for SDL_SetVideoMode or SDL_GL_SetAttribute. Is it possible at all for SDL to ask OpenGL to perform the color correction when writing on the FrameBuffer 0? GLUT seems to be able to provide that functionality.

If SDL cannot do it, what is the usual workaround? I am considering rendering to a sRGB texture with GL_FRAMEBUFFER_SRGB enabled, and then rendering that into the FrameBuffer 0 with FRAMEBUFFER_SRGB disabled. Any better idea?

score 12 · Answer 1 · answered Nov 07 '13 at 16:56

12

Sorry to revive an old question here, but I wanted to note that SDL 2.0.1 will explicitly let you request an sRGB context:

SDL_GL_SetAttribute(SDL_GL_FRAMEBUFFER_SRGB_CAPABLE, 1);
// etc.
SDL_Window *win = SDL_CreateWindow(...);
SDL_GL_CreateContext(win);

This works on Windows and X11 (Mac OS X, etc, doesn't offer this functionality at the moment). It's worth noting that, before SDL 2.0.1 offered this, most GL contexts on modern hardware are already sRGB capable by default. But there you go.

answered Nov 07 '13 at 16:56

Ryan C. Gordon

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Nice! Looking at my packages, it's SDL 1.2.14 that's installed on my system. I didn't know about sRGB available by default, I thought I had to request it. I'm using glfw 3 now, and I am quite happy with it so far, but it's good to know SDL remains an option. – Niriel Nov 08 '13 at 09:24
You may also need to set the alpha bit size, otherwise it's likely you won't get an sRGB framebuffer on Intel drivers (see https://stackoverflow.com/q/44697485/676939) – Alexandros Jun 24 '17 at 10:10

score 5 · Answer 2 · answered Dec 01 '13 at 01:52

To be slightly more precise: You just need to call glEnable(GL_FRAMEBUFFER_SRGB) to make Framebuffer 0 into an SRGB framebuffer.

If you are on SDL2, you should request the capability by calling SDL_GL_SetAttribute(SDL_GL_FRAMEBUFFER_SRGB_CAPABLE, 1) during init, but if you are on an earlier version of SDL, it seems that right now graphics drivers do not care if you request it beforehand.

Nicol Bolas · Accepted Answer · 2013-05-03T12:35:18.120

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The "usual workaround" is "don't use SDL." If your tool doesn't support it, your tool doesn't support it, and that's that.

Your suggested workaround to render to an internal sRGB image is... not as useful as you think.

Will it work? Yes, in the sense that you will get images who's colors are properly gamma correct (though not because of enabling or disabling GL_FRAMEBUFFER_SRGB). However, you will get some degrading of image quality, because the non-linear 24-bit sRGB colorspace does not convert well to a linear 24-bit linearRGB colorspace. You'll lose some color definition.

The point of being able to present an sRGB image directly is to avoid that conversion and the resulting loss of color definition.

Whether you can live with those artifacts is up to you. I'd just as soon avoid using SDL, or hacking SDL to let you do what you need to.

edited May 03 '13 at 12:35

answered May 03 '13 at 11:05

Nicol Bolas

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My goal with disabling GL_FRAMEBUFFER_SRGB before the final write was to prevent the final 'uncorrection'. Wouldn't that work? – Niriel May 03 '13 at 12:19
Damn, no it wouldn't, the flag has no effect on reading. So you're right, this workaround won't work. I guess I'll have to do the correction myself in a shader. – Niriel May 03 '13 at 12:32
I'm writing in Go, so glut isn't really handy. But I found GLFW and it supports sRGB; I'll use that one instead. – Niriel May 08 '13 at 13:38

Can SDL create a sRGB OpenGL context?

3 Answers3