Commit 1183cd4e17675ec699bb0327d9816d0be8af4d4b
2014-07-14T22:30:55
[base] Further clean up color bitmap conversion. * src/base/ftbitmap.c (ft_gray_for_premultiplied_srgb_bgra): Stop using FT_MulFix and FT_DivFix since all calculations fit into 32 bits.
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diff --git a/ChangeLog b/ChangeLog
index f2b3e2b..462881f 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,10 @@
+2014-07-11 Alexei Podtelezhnikov <apodtele@gmail.com>
+
+ [base] Further clean up color bitmap conversion.
+
+ * src/base/ftbitmap.c (ft_gray_for_premultiplied_srgb_bgra): Stop
+ using FT_MulFix and FT_DivFix since all calculations fit into 32 bits.
+
2014-07-13 Werner Lemberg <wl@gnu.org>
[truetype] Improve handling of buggy `prep' tables.
diff --git a/src/base/ftbitmap.c b/src/base/ftbitmap.c
index d0d1ebb..a55038b 100644
--- a/src/base/ftbitmap.c
+++ b/src/base/ftbitmap.c
@@ -378,11 +378,8 @@
static FT_Byte
ft_gray_for_premultiplied_srgb_bgra( const FT_Byte* bgra )
{
- FT_Long a = bgra[3];
- FT_Long b = bgra[0];
- FT_Long g = bgra[1];
- FT_Long r = bgra[2];
- FT_Long l;
+ FT_Byte a = bgra[3];
+ FT_ULong l;
/* Short-circuit transparent color to avoid div-by-zero. */
@@ -397,25 +394,14 @@
*
* http://accessibility.kde.org/hsl-adjusted.php
*
- * We do the computation with integers only.
+ * We do the computation with integers only applying gamma of 2.0,
+ * The following will never overflow 32 bits. This is a scaled up
+ * luminosity with premultiplication not yet undone.
*/
- /* Undo premultification, get the number in a 16.16 form. */
- b = FT_DivFix( b, a );
- g = FT_DivFix( g, a );
- r = FT_DivFix( r, a );
-
- /* Apply gamma of 2.0 instead of 2.2. */
- b = FT_MulFix( b, b );
- g = FT_MulFix( g, g );
- r = FT_MulFix( r, r );
-
- /* Apply coefficients. */
- b = FT_MulFix( b, 4731 /* 0.0722 * 65536 */ );
- g = FT_MulFix( g, 46871 /* 0.7152 * 65536 */ );
- r = FT_MulFix( r, 13933 /* 0.2126 * 65536 */ );
-
- l = r + g + b;
+ l = 4731UL /* 0.0722 * 65536 */ * bgra[0] * bgra[0] +
+ 46871UL /* 0.7152 * 65536 */ * bgra[1] * bgra[1] +
+ 13933UL /* 0.2126 * 65536 */ * bgra[2] * bgra[2];
/*
* Final transparency can be determined this way:
@@ -425,9 +411,10 @@
* - 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
*/
- return a - (FT_Byte)FT_MulFix( l, a );
+ return a - (FT_Byte)( ( l / a ) >> 16 );
}