On Apr 22, 2005, at 10:18 AM, David Niemeijer wrote:
Just to ensure I understand correctly, it accesses and manipulates
the individual pixels of the icon bitmap directly, right? If so, it
sounds like this is a destructive operation requiring the
generation of a copy of the bitmap so that the original is not
Are the exact RGB transforms documented anywhere or could they be
provided on this list, so that for pre-Tiger systems we can do the
same raw pixel manipulations ensuring that an icon drawn by
PlotIconRefInContext would looks exactly the same as a larger
CGImage that we would "transform" ourselves? When icons and images
are mixed in the same window one would prefer to get the same
"looks" when the image need to be disabled or selected.
It looks like we have a "lighten" transformation for the disabled
state and a "darken" transformation for the selected state.
for each pixel component, add 0xFF, and shift right by 1 bit. This
pushes every component towards 0xFFFF.
for each pixel component, shift right by 1
find the component with the largest value, and shift the other two
components right by 1 again. This emphasizes the largest component.
Don't do this step if all of the components (after the first right
shift) are within 0x200 of each other - in this case, we have a gray
pixel, and there's nothing to emphasize.
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