Visibility against an unknown background

Fredrik Lundh fredrik at
Tue Oct 24 22:26:03 CEST 2006

Sergei Organov wrote:

 > > and doesn't work at all on medium gray or b/w dithered patterns.
 > Yes, every method has its pros and cons, but XOR is probably most
 > efficient.

back in the days when backing store was expensive, and memory bandwidth 
was limited, maybe.  contemporary graphics hardware is something radi- 
cally different.

> Where "most cases" depends on application. I'd be very upset to see,
> say, 5-6 highly intersecting scientific plots on the same picture drawn
> using the "marching ants" approach.

but the mostly random colors you get from XOR wouldn't upset your color 
vision subsystem?

to solve your specific case, I'd use bitmask algebra to generate alpha 
layers (or masks/stencil buffers), and use standard compositing to 
generate the final result.


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