[BUG] BitBlt mixup

Helge Horch Helge.Horch at munich.netsurf.de
Tue Feb 27 21:56:35 UTC 2001


Folks,

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:

Open a *vanilla* 3.0final image, and do not move, collapse nor obscure the 
"Welcome" window.  Open a workspace and do:

| p q |
p _ 394 at 261.
q _ p + (200 at 0).
Display
	copy: (p extent: 100 at 100)
	from: Display to: q rule: 3.

and whip out a MagnifierMorph to examine the result.  Here, the first two 
columns look rather odd.  (The "f" of the "for" is missing many bits, while 
the "e" of the "The" is compressed horizontally.)

I thought I was hallucinating -- this couldn't be, someone would have 
noticed long ago.  But the nastiness nastily varies with Squeak's bit 
depth.  With a  graphics card in 32bit mode, the Squeak modes behave as 
follows:

32 bit: effect is hardly noticeable, the "e" is copied, but 1 bit shorter 
(top line: 2 pixels instead of 3),

16 bit: the "e"'s top line is only 1 pixel wide,

8 bit: the "e" is crippled,

4 bit: the "e" is copied intact, but now the "o" of the "for" is missing 
completely,

1 bit: perfect.

I have rummaged through my archive, and a 2.5 VM (win build 6) with an 
accompanying 2.5f1543 does not show these artefacts, at any bitdepth.

Cheers,
Helge 





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