GL_ARB_multisample

[roadkillguy]

So I'm trying to use multisampling to hopefully help some of the jaggedness my application currently has. Unfortunately, glEnable(GL_ARB_multisample) appears to make no difference on my final image. Is this the correct way to use it?

Using glxinfo it appears my system supports GL_ARB_multisample, so I'm not sure what's wrong here.

[Aleksandar]

You need to create a "multisampled" rendering target. Choose pixel format that supports multi-sampling (with appropriate MS factor), or a FBO.

[Ilian Dinev]

Also note that glEnable(GL_MULTISAMPLE) will change nothing, as it's enabled by default.

glEnable(GL_ARB_multisample); // is something invalid

[Dark Photon]

Also note that glEnable(GL_MULTISAMPLE) will change nothing, as it's enabled by default.

Right. Just to clarify the above, you need both of the above to do proper multisample rasterization and downsample filtering:

1. Create a multisampled render target
2. glEnable( GL_MULTISAMPLE ) (or just leave it enabled)

And I have no idea what you're talking about with glEnable( GL_ARB_multisample ). GL_ARB_multisample is the name of an OpenGL extension and not a GL state enable. In glext.h, it is a preprocessor symbol used to prevent multiple includes and is defined to 1 like all other similar preprocessor lock symbols. Your glEnable would translate to glEnable(1) which probably isn't even valid. It's not what you want anyway.

[trinitrotoluene]

Also note that glEnable(GL_MULTISAMPLE) will change nothing, as it's enabled by default.

glEnable(GL_ARB_multisample); // is something invalid

I have an AMD Radeon HD 5870 under Ubuntu and multisampling is not enabled by default with a multisample renderbuffer attached to a FBO. I must call glEnable(GL_MULTISAMPLE) explicitly. On the default framebuffer too I need to explicitly enable multisampling. But unfortunately, since catalyst 11.7 multisampling on the default framebuffer is not working for me.

[roadkillguy]

I see. I didn't know it was an include safety. Either way, given that I have this opengl extension, shouldn't I be able to enable multisampling?

After a bit more research, I'm finding SDL_GL_SetAttribute(SDL_GL_MULTISAMPLESAMPLES, 2); fails with "Couldn't find matching GLX visual" when SDL_SetVideoMode() is called. Maybe it's in my x settings?

[trinitrotoluene]

Did you set also this:

SDL_GL_SetAttribute(SDL_GL_MULTISAMPLEBUFFERS,1);

To get the number of samples available call
glGetIntegerv(GL_SAMPLES,&samples);

On my old computer with nvidia TNT2 with the mesa OpenGL software driver, the extension GL_ARB_multisample was supported but with only one sample per pixel. So check the visual available with glxinfo.In the last column (ms), there is the (ns = number of samples) and (b=number of multisample buffer) listed.

[Ilian Dinev]

I have an AMD Radeon HD 5870 under Ubuntu and multisampling is not enabled by default with a multisample renderbuffer attached to a FBO. I must call glEnable(GL_MULTISAMPLE) explicitly. On the default framebuffer too I need to explicitly enable multisampling.

That's a driver bug then. The spec clearly states that GL_DITHER and GL_MULTISAMPLE are GL_TRUE by default.

[roadkillguy]

Is GL_ARB_multisample unrelated to number of samples and buffer support then?

[trinitrotoluene]

I have an AMD Radeon HD 5870 under Ubuntu and multisampling is not enabled by default with a multisample renderbuffer attached to a FBO. I must call glEnable(GL_MULTISAMPLE) explicitly. On the default framebuffer too I need to explicitly enable multisampling.

That's a driver bug then. The spec clearly states that GL_DITHER and GL_MULTISAMPLE are GL_TRUE by default.

So I have at least two driver bugs. I decided to send my problem to the AMD linux driver crew last week. At least, I have another (easy) way to remove jagged edge with FBO.