MTUG BUG #6 (Melbourne Toolbook User Group Identified Bug)
Subject: Flaw in chromakey behaviour across multiple resolutions
Version: MM Toolbook CBT edition / 3.0a
Detected by: Andy Bulka abulka@empire.com.au
Date: 1-Sep-1995
Description of Crash and probable cause
When you import a graphic and then chromakey it, the
chromakey color gets removed. Fair enough. However
when you switch to a display resolution DIFFERENT to
the resolution that was in effect when you imported
the graphic, the graphic shows residual pixels in
the chromakey color around the edges of the graphic.
NOT a good look. (your mileage may vary - try
experimenting with a few different chromakey bmps).
Mmmmm
What seems to be happening is that the chromakey
algorithm is RESOLUTION DEPENDENT and doesn't
automatically recalculate the chromakey areas
when you switch to a different resolution. I thought
maybe I could repair the situation by setting the
useChromakey property OFF then ON again. But this
does not work! You need to re-import the graphic
in the relevant resolution and set the useChromakey
proprty within that resolution. Yikes!
The bottom line? If you are using chromakey bitmaps
then they will look terrible when viewed in resolutions
different from the one used to construct them.
E.g. If your chromakey color is MAGENTA (as used in the
CBT clip art) and you build your app in VGA mode, then
when running your application in SVGA mode, your graphics
will have ugly magenta edges.
Vice versa - even if you build in SVGA and play in VGA
the same thing will happen.
I think all my dreams of running my app in muliple
resolutions just went out the window.... :-(
The Asymetrix Reply so far
I tried that image on three different machines. It works fine on my machine
with an ATI Ultra (mach 8) runnint Windows NT 3.51 and worked fine on a
Windows 95 machine with an Orchid Fahrenheit 1280 video card, but I got some
residual chromakey color on a Windows machine with a Diamond Stealth VRAM
video card. All machines were in 256 color mode. I tried converting the
image from 256 colors to 16 million and down to 16 colors and got the same
results. I believe this may be a bug. I will submit your grahpic and see
what happens, but I cannot promise anything at this point.
To Reproduce
I just replicated the problem on both Diamond Stealth and Tseng 4000 on
two different machines.
I always work in 256 colors. I jump between VGA(640x480) and 1024x768
and the resulting image has purple/magenta grunge along some of the edges.
Sample Bitmap with problem
END BUG REPORT.
webster@son.washington.edu
University of Washington
Box 357260
Seattle, WA 98195-7260
206/543-9175
