[PATCH 3/4] Always round glyph advance in 26.6 space

[Matthias Dahl]

From: Matthias Dahl <matthias.dahl at binary-island.eu>
Date: Tue, 27 Dec 2016 19:30:13 +0100
Subject: [PATCH 3/4] Always round glyph advance in 26.6 space

By rounding in the 26.6 space, the glyph advance can be snapped to the
next 64 boundary by integer arithmetic alone, thus avoiding floating
arithmetic and improving accuracy.
---
 src/share/native/sun/font/freetypeScaler.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/src/share/native/sun/font/freetypeScaler.c b/src/share/native/sun/font/freetypeScaler.c
index 296737eac..3d67cce9b 100644
--- a/src/share/native/sun/font/freetypeScaler.c
+++ b/src/share/native/sun/font/freetypeScaler.c
@@ -49,7 +49,7 @@
 #define  FloatToFTFixed(f) (FT_Fixed)((f) * (float)(ftFixed1))
 #define  FTFixedToFloat(x) ((x) / (float)(ftFixed1))
 #define  FT26Dot6ToFloat(x)  ((x) / ((float) (1<<6)))
-#define  ROUND(x) ((int) (x+0.5))
+#define  ROUND26Dot6(x) ((x + 63) & -64)
 
 typedef struct {
     /* Important note:
@@ -947,12 +947,12 @@ Java_sun_font_FreetypeFontScaler_getGlyphImageNative(
     } else {
         if (!ftglyph->advance.y) {
             glyphInfo->advanceX =
-                (float) ROUND(FT26Dot6ToFloat(ftglyph->advance.x));
+                (float) FT26Dot6ToFloat(ROUND26Dot6(ftglyph->advance.x));
             glyphInfo->advanceY = 0;
         } else if (!ftglyph->advance.x) {
             glyphInfo->advanceX = 0;
             glyphInfo->advanceY =
-                (float) -ROUND(FT26Dot6ToFloat(ftglyph->advance.y));
+                (float) -FT26Dot6ToFloat(ROUND26Dot6(ftglyph->advance.y));
         } else {
             glyphInfo->advanceX = FT26Dot6ToFloat(ftglyph->advance.x);
             glyphInfo->advanceY = FT26Dot6ToFloat(-ftglyph->advance.y);
-- 
2.11.0