bell@eniac.seas.upenn.edu (Mike Bell) (01/03/90)
Here is an undocumented oddity I found with the 32 bit QD in the IIci. We
have an application that uses off screen bit maps, as defined by 32 bit
Quickdraw. After setting up the offscreen bitmap with a NewGWorld call, the
32 bit Quickdraw documentation from APDA states that the off screen bit map
(GWorld) can be accessed directly if certain precautions are taken. The
pixmap must be locked and made unpurgeable with the LockPixels and
NoPurgePixels calls. Once these calls are made, a call to GetPixBaseAddress
returns a 32 bit pointer to the offscreen PixMap. Here is where things get
interesting.
On all machines but the IIci, this works great; we can write directly to the
pixmap, and then let QuickDraw actually do the display (copybits). On the IIci
(using the built in video) however, when we write to the address that we are
passed, we obliterate the screen !! Even if the video is mapped by the MMU,
the offscreen bitmaps shouldn't necessarily have to be. In fact, this would
suggest that 32 bit QD has been modified on the IIci to allow an offscreen
bit map (created by 32 bit QD) to be placed at a specific location in memory.
I would be VERY pleased if this ability actually did exist; putting an
offscreen bitmap on an arbitrary video card would sure help to speed up
animation (no bus accesses necessary)......
Can anyone shed some light on these IIci oddities ???
Mike Bell
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Mike Bell CSnet: BELLMA%ERVX01@dupont.com
Senior Engineer Applelink: D2747
DuPont Electronic Imaging
Core Technology Group
MacBrisc..... When you feel the need for speed..........
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