| From: | David McMinn |
| Date: | 26 May 2001 at 15:26:08 |
| Subject: | Re: Corrupt Display |
On 26 May 2001, at 14:47, Jason Faramus wrote:
> Has anyone who has tried the old Crap Fighter demo experienced screen
> corruption, i.e. flickering lines etc... as it seems to happen on my Amiga and
> also happens with Worms DC (also Blitz made I believe) Is this a fault with
> Blitz maybe the Display Scroll command or is it my Amiga? If anyone can offer
It would only be a fault of the DisplayScroll command if someone used it
wrongly.
For example, if you try to scroll lines further than the edges of the
bitmap, you will either get graphical corruption or the egdes of the
previous/next lines appearing.
Another problem could be if your coplist is set up wrongly so that custom
copper instructions overlap. Weird things would definately happen then.
You will also get problems if your custom copper instructions take up too
much time in the video frame. If you run too far off the end of the
timing of a frame, there might be problems with the start of the next
frame. You might get similar problems on a per line basis, in that if you
put too many copper instructions per line subsequent copper instructions
will be performed at incorrect times.
The final problem that I can think of is if you try to use displayscroll
to jump about a bitmap too much. (It will automatically change the pixel
distance you move so that it moves up to 16 pixels and then for every 16
pixels it will change the start address of the bitmap being displayed. I
think the maximum you can move is +/-32k pixels.) The specific example I
was thinking of was a game where the programmers were using a hugely wide
bitmap and at the bottom they tried to do a mirror reflection of the
lower part of the bitmap. They had used DisplayScroll to move the bitmap
pointers and give it a wobbly water effect, but they could only do a few
lines due to the limitations above. So make sure you're not trying to
exceed the limitations of what the hardware can do.
|) /\ \/ ][ |) |\/| c |\/| ][ |\| |\| | dave@blitz-2000.co.uk
http://members.nbci.com/david_mcminn | ICQ=16827694
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