View Full Version : Overlay/Underlay planes in depth?

09-29-2006, 08:44 AM
The FAQ has a pretty anemic paragraph about overlay planes and how to use them in WGL. I've searched every bookstore I know of and I can't find anything that cares to cover overlay planes. They all act like overlay planes are outdated, but I can think of plenty of uses.

Can anyone help me out? Some examples or some better documentation?


09-29-2006, 10:30 AM
Ahh, as far as I know they are not supported by consumer graphics cards, only by some professional cards (like Quadro) - not sure about that though.

09-29-2006, 03:16 PM
Yes, perhaps it's better to forget about overlay/underlay planes. These can be emulated by rendering your overlays/underlays to offscreen buffers/textures and a composition with your main scene using blending.

Once FBO multisampling is a reality, this composition technique will generalize very nicely, and be totally platform independent.

09-29-2006, 04:26 PM
If you do happen to have a card that supports these planes, you might be interested in this (http://www.xmission.com/~nate/siggraph97/notes/overlay.htm) .

09-30-2006, 06:39 AM
The whole idea of overlay plane is that you do not damage the main plane with your second plane drawings... saving you losts of unessary redraws... but I guess that this concept of simple and basic separation of the drawing plane are only applicable for serious graphics apps. I dont agree!

As for code, you could also look at the green book in the OpenGL series... That's the one focusing on X Windows, but the code is mostly applicable.

Then, you've got the Qt4 APi from Trolltech that has a very neat set of features for there QGLWidget.

Overlay's are style used in professional software in the CAD/CAM, Fx, CG and the likes...