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From: | Huang Koffman |
Subject: | [ft-devel] coverage algorithm of ft_grays.c ? |
Date: | Wed, 27 Jun 2007 13:10:09 +0800 |
Dear David,
I try to trace ft_grays.c for speed up. And I have some question. Can you tell me please.
I cannot understand the coverage algorithm.
1. As below, Coverage = area/(Pixel_Bit*Pixel_Bit/2) why?
/* compute the coverage line's coverage, depending on the */
/* outline fill rule */
/* */
/* the coverage percentage is area/(PIXEL_BITS*PIXEL_BITS*2) */
/* */
coverage = (int)( area >> ( PIXEL_BITS * 2 + 1 - 8 ) );
/* use range 0..256 */
2.The area value should be "(fx1+fx2)/2*delta" if it is a trapezoid. But not in below code. Why?
/* everything is located in a single cell. That is easy! */
/* */
if ( ex1 == ex2 )
{
delta = y2 - y1;
ras.area += (TArea)( fx1 + fx2 ) * delta;
ras.cover += delta;
return;
}
Regards,
Koffman
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