Re: Crash within WinCopyRectangle

[Ken Krugler]

Ken Krugler a Ècrit :

 > >When running my program on a OS 3.5 IIIc, the map pan feature based on
 >WinCopyRectangle (following stylus moves) often crashes with the
 > >following stack crawl (seen in the CW 8.3 debugger):
 > >
 >MapHandleEvent( EventType* )
 >0x10C55E52( WinCopyRectangle )
 >0x10C4E0D2( BltCopyRectangle )
 >0x10C4E0D2( BltCopyRectangle )
 >0x10C51E32( PrvMisAlignedBackwardInnerBitBlt¡ )
 >
 > >What can I do about this (other than telling my user to ditch his IIIc)?
 >I never saw this occur on another device, monochrome or color.

 I ran into the same problem with some picture pan code. From an old post...

 > At 12:25 PM -0800 2/17/01, Ken Krugler wrote:
 >2. When calling WinCopyRectangle(screen,
 >off-screen) and the off-screen window uses a
 >bitmap without a color table, then Palm OS 3.5
 >will accidentally dispose of the system color
 >table, and a subsequent call will die in Poser.
 >I think this same situation might occur in the
 >inverse case as well.
 The full post is at <http://www.escribe.com/computing/pcpqa/m34989.html>

 I fixed it in my code by making sure the 
off-screen bitmap had a color table.
In my case, I'm just moving the screen window 
onto itself, drawing from screen to screen:

WinCopyRectangle( NULL, NULL, &bounds, newX - 
screenX, newY - screenY, winPaint );

How could the screen window not have a color table?
It should. But the specific bug was in the 
low-level blitter code, where it was incorrectly 
disposing of a color table that it _thought_ it 
had allocated, but was in fact (in my case) the 
system color table that's used when the 
destination bitmap doesn't have a color table.

So there may be other ways in which the same bug 
could be triggered. However rectangle to 
rectangle copying from the screen is something 
that gets used a lot, which makes me suspect 
something in your code that's trashing memory. 
Have you been running on POSER with a IIIc debug 
ROM and all debug checks turned on?

-- Ken
--
Ken Krugler
TransPac Software, Inc.
<http://www.transpac.com>
+1 530-470-9200
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