GL_ARB_multisample

[Alfonse Reinheart]

Multisampling is a function of the framebuffer. However, OpenGL does not define the contents of the default framebuffer; the stuff that initializes an OpenGL context does. So you need to use those APIs to make multisampling possible, and then use what's in GL_ARB_multisample to activate multisampled rendering.

[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.

[roadkillguy]

In essence, I have an opengl extension I can't use?

[Alfonse Reinheart]

Define "can't use".

What you can and cannot use is based on what you're doing. You don't have to create a multisampled default framebuffer to do multisampled rendering, but you do have to have some framebuffer (whether an FBO or the default) that has multisampled images in it to render with multisampling.

If SDL isn't able to give you a multisampled framebuffer, then it sounds like you either need to use something else to create your context or build multisampled images manually and use FBOs. You can blit to the non-multisampled default framebuffer.