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Minor.

This commit is contained in:
Werner Lemberg 2014-07-17 17:24:22 +09:00
parent c0a6f20a4b
commit 3939c200f3
1 changed files with 7 additions and 4 deletions
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11
src/base/ftbitmap.c
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@ -394,9 +394,10 @@
*
* http://accessibility.kde.org/hsl-adjusted.php
*
* We do the computation with integers only applying gamma of 2.0,
* The following will never overflow 32 bits. This is a scaled up
* We do the computation with integers only, applying a gamma of 2.0.
* The following will never overflow 32 bits; it is a scaled-up
* luminosity with premultiplication not yet undone.
*
*/
l = 4731UL /* 0.0722 * 65536 */ * bgra[0] * bgra[0] +
@ -404,14 +405,16 @@
13933UL /* 0.2126 * 65536 */ * bgra[2] * bgra[2];
/*
* Final transparency can be determined this way:
* Final transparency can be determined as follows.
*
* - If alpha is zero, we want 0.
* - If alpha is zero and luminosity is zero, we want 255.
* - If alpha is zero and luminosity is one, we want 0.
*
* So the formula is a * (1 - l) = a - l * a.
* Undoing premultiplication and scaling back down we get
*
* In the actual code, we undo premultiplication and scale down again.
*
*/
return a - (FT_Byte)( ( l / a ) >> 16 );