[BUG] BitBlt mixup

Dan Ingalls Dan.Ingalls at disney.com
Thu Mar 1 02:00:22 UTC 2001


Helge Horch <Helge.Horch at munich.netsurf.de> wrote...
>I'm seeing really weird BitBlt artefacts on my Windoze machines, and I 
>can't fix it myself.  The following is reproducible on all my machines, 
>systems (NT/98) and VMs (3.0bld2, 3.0bld1, even 2.8bld-a2).  I'd be curious 
>whether Mac and Unix users get this, too:

Here's a fix, which should soon make it through the update process.

	- Dan

As it says in the preamble...
-----------------
Fixes a bug introduced in changSet 1945BitBltSpeedup, and discovered by Helge Horch.
It had resulted in different results in the upper and lower copies displayed during the following loop (the upper copy results from a blt with src==dest, delta y = 0, and delta x > 0, the only case for which the horizontal loop must proceed from right to left):

	| p q |
	[Sensor anyButtonPressed] whileFalse:
	[p _ Sensor cursorPoint.
	q _ p + (200 at 0).
	Display fillWhite: ((q extent: 50 at 60) expandBy: 10).
	Display copy: (p extent: 50 at 30)
		from: Display to: q rule: 3.
	Display copy: (p extent: 50 at 30)
		from: Display to: q + (0 at 31) rule: 3.
	(Delay forMilliseconds: 200) wait].

This change purports to fix the problem for all color depths.
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