CODEWITHSUNDEEP
macoscocoaopenglopengl-3
tmlen
tmlen

Reputation: 9090

Changing default OpenGL context profile version

To create an OpenGL context with profile version 3.2, I need to add the attributes to the pixel format when creating the context:

...,
NSOpenGLPFAOpenGLProfile, (NSOpenGLPixelFormatAttribute) NSOpenGLProfileVersion3_2Core,
...,

Is there a way (environment variable, global variable, function to call before the NSOpenGLPixelFormat is created, ...), to alter the default OpenGL profile version, for when no such attributes are specified. It defaults to an older version on OS X 10.10. I'm trying to integrate code that relies on newer OpenGL features with a framework (ROOT) that sets up the OpenGL context and gives no way to alter the parameters.

And is there a way to change the pixel format attributes of an OpenGL context after it has been set up?

Upvotes: 1

Views: 586

Answers (1)

Andon M. Coleman
Andon M. Coleman

Reputation: 43319

Pixel formats associated with OpenGL contexts (the proper terminology here is "default framebuffer") are always immutable. OpenGL itself does not control or dictate this, it is actually the window system API (e.g. WGL, GLX, EGL, NSOpenGL) that impose this restriction.

The only way I see around this particular problem is if you create your own offscreen (core 3.2) context that shares resources with the legacy (2.1) context that ROOT created. If OS X actually allows you to do this context sharing (it is iffy, because the two contexts probably count as different renderers), you can draw into a renderbuffer object in your core context and then blit that renderbuffer into your legacy context using glBlitFramebuffer (...).

Note that Framebuffer Objects are not a context shareable resource. What you wind up sharing in this example is the actual image attachment (Renderbuffer or Texture), and that means you will have to maintain separate FBOs with the same attachments in both contexts.

Upvotes: 1

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