Commit 0e0fdc5dc89e5079898c5da67b56f994c439fee1
2013-01-12T23:05:55
[truetype] Improve accuracy of normalization of short vectors. Unit vector components are stored as 2.14 fixed-point numbers. In order to calculate all 14 bits accurately, a short vector to be normalized has to be upscaled to at least 14 bits before its length is calculated. This has been safe since accurate CORDIC algorithms were adopted. * src/truetype/ttinterp.c (Normalize): Scale short vectors by 0x4000.
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diff --git a/ChangeLog b/ChangeLog
index 4b35164..07931d1 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,17 @@
2013-01-12 Alexei Podtelezhnikov <apodtele@gmail.com>
+ [truetype] Improve accuracy of normalization of short vectors.
+
+ Unit vector components are stored as 2.14 fixed-point numbers. In
+ order to calculate all 14 bits accurately, a short vector to be
+ normalized has to be upscaled to at least 14 bits before its length
+ is calculated. This has been safe since accurate CORDIC algorithms
+ were adopted.
+
+ * src/truetype/ttinterp.c (Normalize): Scale short vectors by 0x4000.
+
+2013-01-12 Alexei Podtelezhnikov <apodtele@gmail.com>
+
[truetype] Kill very old vector normalization hacks.
Back in the days, vector length calculations were not very accurate
diff --git a/src/truetype/ttinterp.c b/src/truetype/ttinterp.c
index f862320..1cbb351 100644
--- a/src/truetype/ttinterp.c
+++ b/src/truetype/ttinterp.c
@@ -2635,8 +2635,6 @@
/* In case Vx and Vy are both zero, Normalize() returns SUCCESS, and */
/* R is undefined. */
/* */
-
-
static FT_Bool
Normalize( EXEC_OP_ FT_F26Dot6 Vx,
FT_F26Dot6 Vy,
@@ -2647,17 +2645,17 @@
FT_UNUSED_EXEC;
- if ( FT_ABS( Vx ) < 0x10000L && FT_ABS( Vy ) < 0x10000L )
+ if ( FT_ABS( Vx ) < 0x4000L && FT_ABS( Vy ) < 0x4000L )
{
- Vx *= 0x100;
- Vy *= 0x100;
-
if ( Vx == 0 && Vy == 0 )
{
/* XXX: UNDOCUMENTED! It seems that it is possible to try */
/* to normalize the vector (0,0). Return immediately. */
return SUCCESS;
}
+
+ Vx *= 0x4000;
+ Vy *= 0x4000;
}
W = TT_VecLen( Vx, Vy );