View Full Version : OpenGL Overlays Help!

05-18-2002, 02:03 AM
Alright, while I've read that Microsoft Windows has no support for OpenGL's Overlays and Underlays (is this correct? not sure), I would like to know how would an OpenGL programmer do the same? Assuming I want my code to be portable.

(Do 3D Cards actually have overlays/underlays that you could use?)


05-18-2002, 06:38 AM
A hardware overlay is different to what I think you might mean, which is the stencil buffer.

DirectX supports hardware overlays (of course), OpenGL does not. OpenGL support stencil buffers for in-scene masking of pixels you don't want to be written over stuff that already exists in your scene.

If you mean the latter method (ie. showing an unchanging cockpit display while rendering a 3d scene through the `windows'), then OpenGL does support this - I'm not sure about DirectX however.

05-19-2002, 02:47 AM
i mean, when you define your pixelformatdescriptor, you specify the main_plane right? but you can't use an overlay plane or an underlay plane, is this correct? if so, how can we use them? and when and where can we use these overlay/underlay plane?

stencil buffer is usually hardware accelerated, am i right? what is difference in usage of overlay/underlay/stencil ???

(I'm a beginner, obviously, so sorry if i ask too many! http://www.opengl.org/discussion_boards/ubb/frown.gif )