Overlay planes: a question for the Factory

[Wes Macaulay]

Can anyone comment on overlay planes as mentioned in Revit 7's Options dialog? I know they're a feature of OpenGL... but is this a feature used by only some cards? Which cards? In our experience, the use of overlay planes reduces video performance, presumably because the video card doesn't support them in Revit. Would it be a benefit to use a card which supports overlay planes in Revit rather than one that merely supports OpenGL acceleration?

Are overlay planes a new development in graphic card technology? I've tried reading up on them, but the pages didn't read like English!

[FK]

Revit overlay planes are different from OpenGL overlay planes. Cards that adequately support OpenGL overlays cost $1000+, so we did not aim at them.

Basically, overlays cache images for faster redraws. So, they do not improve interactive response, and may slightly slow it down on some cards. They are aimed at improving performance when switching between open views or applications.

[beegee]

I've been researching some graphics cards and came across this comment from Leadtec, explaining one of the differences between a Quadro and a GeForce card...( Quadro has overlays and GeForce does not )

Hardware overlay planes


The user interface of many professional applications often require elements to be interactively drawn on top of a 3D model or scene. The cursor, pop-up menus or dialogs will appear on top of the 3D-viewport. These elements can damage the contents of the covered windows or affect their performance and interactivity.


To avoid this, most professional applications use overlay planes. Overlay planes allow items to be drawn on top of the main graphics window without damaging the contents of the windows underneath. Windows drawn in the overlay plane can contain text, graphics etc - the same as any normal window.


The planes also support the transparency function, which when set allows pixels from underneath the overlayed window to show through. They are created as two separate layers. This prevents possible damage to the main graphics window and it also improves performance. Likewise, showing an overlayed window as transparent with graphics inside allows items in the user interface to be drawn over the main graphics window.
Clearing and redrawing only the overlayed window is significantly faster than redrawing the main graphics window. This is how animated user-interface components can be drawn over 3D models or scenes.

[Wes Macaulay]

Thanks, Fedor. Is there much likelihood that any video card is likely to support Revit's implementation of overlay planes, then? Any clues to which cards do support them? Does it matter much?

Thanks for the overlay heads up, Beegee. Would be interesting to test both of those cards to see if they make any difference in Revit.

[FK]

The card does not need to do anything particular - just handle the bitmaps well. I don't know much about specific models, but NVidia seems to be most reliable at the moment. Huge video RAM is not important currently.

[Wes Macaulay]

So if I've loaded a raster image into Revit, overlay planes will improve performance in those views? Importing images into views has quite an impact on video performance!

[FK]

I wouldn't hold my breath, but you can try it for yourself...