cullip@pooh.cs.unc.edu (Timothy Cullip) (10/05/90)
Can someone explain to me why a 2D graphics accelerated DEC5000 (this is the PX model) doesn't handle animated sequences well? Specifically, I have a display program that creates a sequence of pixmaps (one for each frame of a precomputed animation). Once they are all created I do a simple loop which copies each successive pixmap into the onscreen window. On a DEC 3100 this works fine for large sequences (for example 50 frames of 256x256 pixmaps). I can easily get over 10 frames/second. On a DEC 5000 PX up to about 10 frames can go blazingly fast (looks like about 30 frames/second or more), but anything over a certain total size and number (usually in the range of about 1Mbyte of total pixmap memory) and suddenly things slow to a craw. For example the first 10 frames may go at the 30 frame/sec rate, but then the others go at about 2 frames/sec. When it loops back to those first 10, they go fast again, and the others still go slow. This is rather annoying to see part of the animation go lightning fast and the rest of it to crawl along slowing. This is not a disk swapping problem! The program happily gets everything into memory. My best uneducated guess is that the PX model (and most likely all the more expensive versions above it) separate frame buffer memory (of which it has 2 screens worth) from main memory and the CPU. If you have only a few windows or pixmaps, they can be held in the off screen frame buffer memory and copied into an onscreen window rapidly. If you have more than can be held in the frame buffer, then the extras reside in the CPU's main memory space and probably have to be suffled through the accelerators (misnomer in this situation) hardware to get to the frame buffer. Anyways, I'm looking for people that have had similar experiences that might be able to shed some light on the situation. Especially if you know if there is a fix to this problem. I'd hate to have to drop back to a CX model just because a PX wasn't designed to do large numbers of pixmap to window copies. Tim Cullip cullip@cs.unc.edu Tim Cullip cullip@cs.unc.edu