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Club Amiga de Montreal - CAM
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fspots.doc
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1986-11-20
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FSPOTS is a replacement for the painfully slow "spots" demo on
the workbench disk. It uses a high-preformance ellipse generator and
generates an average of 63 ellipses per second on a 640x200 workbench
window. Besides being a lot faster, it is also much smaller (even though
it contains its own ellipse generator).
This program probably cannot be sped up by more than 15%.
I think that the method used is the best way to use the blitter to aid
in the generation of filled ellipses in Intuition windows:
(1) clear an area in a temporary raster equal to the size of
the upper half of the ellipse
(2) Draw the outline of the upper half of the ellipse in the
temprast, generating 1 dot per scanline. Use symetry for
the right and left halves.
(3) Fill the half ellipse in the raster with the blitter.
(4) Use the blitter to mirror the filled top half down into the
bottom half.
(5) Use BltTemplate or BltPattern to copy the raster into the
target rastport.
The only problem with this demo is that it is TOO fast! The ellipses
flicker a lot because the pixel values are continually being overwritten.
The ellipses don't flash any more than the one in the normal spots demo, but
the pixels don't stay stable for very long.
This program may be freely distributed.
Chris Green
Prospect Software
P.O. Box 343
Champaign, IL 61820-3403