As the title suggests, I'm using Qt for OpenGL drawing, and with QOpenGLWidget I can turn on multisampling for the main screen buffer with QSurfaceFormat's setSamples() function. This works fine and looks pretty nice. However, I'm also drawing into a custom frame buffer (using glGenFramebuffers, glBindFramebuffer(), etc) in the background, where I don't want anti-aliasing (since it's drawing using color encoding for selection purposes), but it seems to be inheriting the multi-sampling from the main QOpenGLWidget somehow. Any ideas on how to disable that, to use multisampling in the main window but not in my own custom off-screen frame buffers?
2 Answers
Multisampled rendering is enabled or disabled by using the glEnable/Disable(GL_MULTISAMPLE). This state is not part of the framebuffer's state; it's regular context state. As such, even when you switch framebuffers, that state will be unaffected.
Additionally, the multisample enable/disable switch doesn't mean anything if your attached images don't have multiple samples. If you're creating images for non-multisampled rendering, there's no reason to create them with multiple samples. So create single-sample images.
Comments
Well, couldn't find a way to disable it or avoid it in my OpenGL code, but if I set the default format to have 0 samples and the format of the QOpenGLWidget to have 2/4/8/whatever, then the framebuffer object won't use anti-aliasing when it's created.