Interesting.
I can't see an obvious problem in the shaders yet.
I tested various display modes and the ones which give weird results after a short delay all have screen height/width ratios less than 0.75. The ones which seem to work all have ratios of 0.75 or 0.8 such as 1600x1200 (ratio=0.75) and 1280x1024 (ratio = 0.8). This suggests something in the code or a shader is making an assumption about the ratio.
Another clue is that the problem kicks in after a short delay. One thing which does that is the "cheapmotionblur" section of the dba code:
rem cheap motion blur (I want the motion blur used in project offset)
if cheapmotionblur#<100
inc cheapmotionblur#,0.25 ` problem goes away if this line is commented
if cheapmotionblur#>=100
set object effect 1,21
else
bluruse#=cheapmotionblur#
if bluruse#<60.0 then bluruse#=60.0
set alpha mapping on 1,bluruse#
endif
endif
If you stop the controlling variable from changing then the problem goes away (see my comment in the above snippet).
So it looks like something to do with object 1 and shader 21. Perhaps someone else can take it from here? My brain hurts.
In short, I very much doubt there's a problem with your PC.
You could try different valid screen widths and heights in the following lines in the dba code (make sure they match):
set display mode 1024,768,32,0
make camera 1 : set camera to image 1,1,1024,768,2
make camera 5 : set camera to image 5,55,1024,768
I did it by replacing the values with variables sw and sh which I set in a convenient spot near the top of the code.
Edit There are at least two objects which seem to involve the ratio 0.75 - objects 1 and 8. There may be another somewhere. I'm sure a simple fix is possible - eventually.
