Don't always enable GL_FRAMEBUFFER_SRGB

[nstoddard]

I'm working on an application that uses FXAA. The output didn't look quite right, and it turns out it's because glium is automatically enabling GL_FRAMEBUFFER_SRGB. There doesn't seem to be any way to disable this - I had to modify the glium source code to disable it. There needs to be a way to disable it, or maybe it should be disabled by default and you would provide a draw parameter to enable it.

There's also some systems that don't support GL_FRAMEBUFFER_SRGB, which would cause output on those systems to look bad. Is there a way for glium to detect if it's not supported, and emulate it with a shader instead?

[tomaka]

My idea was to add a flag to programs that tells whether the program outputs sRGB or linear RGB. Glium would disable GL_FRAMEBUFFER_SRGB if the program outputs sRGB, and enable it if it doesn't. Would that make sense?

There's also some systems that don't support GL_FRAMEBUFFER_SRGB, which would cause output on those systems to look bad.

Actually if I'm not mistaken it would look exactly the same.

[tomaka]

Another option for you is to simply render the intermediate image into an SrgbTexture2d instead of a Texture2d.

[nstoddard]

Another option for you is to simply render the intermediate image into an SrgbTexture2d instead of a Texture2d.

I tried this, and unfortunately it doesn't seem to work - the output is exactly the same. I could be doing something wrong though.

My idea was to add a flag to programs that tells whether the program outputs sRGB or linear RGB.

That sounds like it would be fine. Would this be an extra parameter to Program::from_source?

Regarding sRGB not being supported everywhere, I was working on a game a while back that worked fine on my system, but on someone else's system the output was darker than it should be. I think the problem was that the system didn't have sRGB capable framebuffers, so GL_FRAMEBUFFER_SRGB didn't do anything. I ended up having to do the conversion myself in the shaders, with code like out_color = pow(color, vec4(1.0/2.2,1.0/2.2,1.0/2.2,1.0));.

[tomaka]

That sounds like it would be fine. Would this be an extra parameter to Program::from_source?

Actually the flag already exists, I just don't know where to put in in the program creation API.
(the program creation API is still a bit blurry to me because I don't want to close the door to awesome things in the future, like compile-time introspection of the GLSL code)