Doh...brain meltdown. You are right, I was thinking color buffer.
However, it is also possible that the zbuffer is not cleared. If you dont know, there is a trick you can do where (with a zrange of 0 to 1) you use NearClipPlane=0.0, FarClipPlane=0.5 on frame with a Z compare of <=, and then the next frame use NearClipPlane=1.0, FarClipPlane=0.5 with a Z compare of >=, then repeat this process every 2 frames.
I am NOT saying UT does this, just speculating that it COULD. perhaps a run of glTrace could tell you.
i have put my screenshot function into ClearZ() to test, so every it should make a screenshot. i was running the intro scene. a few seconds it runs smooth and then it gets interupted. later i checked that realy no screenshot was written before this interuption.
"Changing UseZTrick=1 to 0 can fix Z-buffer related problems, although as above may reduce performance. You can also fix Z-buffer errors by running the game with a 32-bit colour depth."
Nothing more. This might be the trick I just mentioned earlier, as that trick does increase performance (by avoiding a clear) and it can cause z artifacts (as it wastes 1 bit of precision, since only half the zbuffer is used each frame). Try disabling it, I have a feeling ClearZ() will get called
No input will be available in its slowed down state? Surely you jest. The only problem with my suggestion is that it takes a lot of knowledge he most likely doesn''t have. More importantly the value of that knowledge for him is most likely substantially less than the cost of acquiring it. I might be a bit cheaper to buy a video card with a composite or s-video output. That would be too easy though.