Quantize kerning adjustment, otherwise all the metrics hinting effort will

2007-04-12  Behdad Esfahbod  <behdad@gnome.org>

        * pango/pango-ot-buffer.c (apply_gpos_ltr), (apply_gpos_rtl),
        (pango_ot_buffer_output):
        * pango/pango-types.h:
        * pango/pangofc-font.c (pango_fc_font_kern_glyphs):
        * pango/pangofc-private.h:
        Quantize kerning adjustment, otherwise all the metrics hinting
        effort will be ruined by a non-whole-pixel kerning value.
        In the future we want to take lsb_delta and rsb_delta into the
        game before quantizing the adjustment here, but we don't have
        those values handy right now.


svn path=/trunk/; revision=2225

5 files changed, 60 insertions, 19 deletions

diff --git a/ChangeLog b/ChangeLog
index 2d4ea3dc..ce6ffa45 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,16 @@
+2007-04-12  Behdad Esfahbod  <behdad@gnome.org>
+
+	* pango/pango-ot-buffer.c (apply_gpos_ltr), (apply_gpos_rtl),
+	(pango_ot_buffer_output):
+	* pango/pango-types.h:
+	* pango/pangofc-font.c (pango_fc_font_kern_glyphs):
+	* pango/pangofc-private.h:
+	Quantize kerning adjustment, otherwise all the metrics hinting
+	effort will be ruined by a non-whole-pixel kerning value.
+	In the future we want to take lsb_delta and rsb_delta into the
+	game before quantizing the adjustment here, but we don't have
+	those values handy right now.
+
 2007-04-09  Behdad Esfahbod  <behdad@gnome.org>
 
 	* === Released 1.16.2 ===
diff --git a/pango/pango-ot-buffer.c b/pango/pango-ot-buffer.c
index 539d5fd9..ca1ae99d 100644
--- a/pango/pango-ot-buffer.c
+++ b/pango/pango-ot-buffer.c
@@ -22,9 +22,7 @@
 #include <config.h>
 
 #include "pango-ot-private.h"
-
-#define PANGO_SCALE_26_6 (PANGO_SCALE / (1<<6))
-#define PANGO_UNITS_26_6(d) (PANGO_SCALE_26_6 * (d))
+#include "pangofc-private.h"
 
 /**
  * pango_ot_buffer_new
@@ -198,7 +196,8 @@ swap_range (PangoGlyphString *glyphs, int start, int end)
 
 static void
 apply_gpos_ltr (PangoGlyphString *glyphs,
-		HB_Position      positions)
+		HB_Position      positions,
+		gboolean         is_hinted)
 {
   int i;
 
@@ -208,6 +207,19 @@ apply_gpos_ltr (PangoGlyphString *glyphs,
       FT_Pos y_pos = positions[i].y_pos;
       int back = i;
       int j;
+      int adjustment;
+
+
+      adjustment = PANGO_UNITS_26_6(positions[i].x_advance);
+
+      if (is_hinted)
+	adjustment = PANGO_UNITS_ROUND (adjustment);
+
+      if (positions[i].new_advance)
+	glyphs->glyphs[i].geometry.width  = adjustment;
+      else
+	glyphs->glyphs[i].geometry.width += adjustment;
+
 
       while (positions[back].back != 0)
 	{
@@ -221,17 +233,13 @@ apply_gpos_ltr (PangoGlyphString *glyphs,
 
       glyphs->glyphs[i].geometry.x_offset += PANGO_UNITS_26_6(x_pos);
       glyphs->glyphs[i].geometry.y_offset -= PANGO_UNITS_26_6(y_pos);
-
-      if (positions[i].new_advance)
-	glyphs->glyphs[i].geometry.width  = PANGO_UNITS_26_6(positions[i].x_advance);
-      else
-	glyphs->glyphs[i].geometry.width += PANGO_UNITS_26_6(positions[i].x_advance);
     }
 }
 
 static void
 apply_gpos_rtl (PangoGlyphString *glyphs,
-		HB_Position      positions)
+		HB_Position      positions,
+		gboolean         is_hinted)
 {
   int i;
 
@@ -243,6 +251,19 @@ apply_gpos_rtl (PangoGlyphString *glyphs,
       FT_Pos x_pos = positions[i_rev].x_pos;
       FT_Pos y_pos = positions[i_rev].y_pos;
       int j;
+      int adjustment;
+
+
+      adjustment = PANGO_UNITS_26_6(positions[i_rev].x_advance);
+
+      if (is_hinted)
+	adjustment = PANGO_UNITS_ROUND (adjustment);
+
+      if (positions[i_rev].new_advance)
+	glyphs->glyphs[i].geometry.width  = adjustment;
+      else
+	glyphs->glyphs[i].geometry.width += adjustment;
+
 
       while (positions[back_rev].back != 0)
 	{
@@ -258,11 +279,6 @@ apply_gpos_rtl (PangoGlyphString *glyphs,
 
       glyphs->glyphs[i].geometry.x_offset += PANGO_UNITS_26_6(x_pos);
       glyphs->glyphs[i].geometry.y_offset -= PANGO_UNITS_26_6(y_pos);
-
-      if (positions[i_rev].new_advance)
-	glyphs->glyphs[i].geometry.width  = PANGO_UNITS_26_6(positions[i_rev].x_advance);
-      else
-	glyphs->glyphs[i].geometry.width += PANGO_UNITS_26_6(positions[i_rev].x_advance);
     }
 }
 
@@ -350,9 +366,9 @@ pango_ot_buffer_output (PangoOTBuffer    *buffer,
   if (buffer->applied_gpos)
     {
       if (buffer->rtl)
-	apply_gpos_rtl (glyphs, buffer->buffer->positions);
+	apply_gpos_rtl (glyphs, buffer->buffer->positions, buffer->font->is_hinted);
       else
-	apply_gpos_ltr (glyphs, buffer->buffer->positions);
+	apply_gpos_ltr (glyphs, buffer->buffer->positions, buffer->font->is_hinted);
     }
   else
     pango_fc_font_kern_glyphs (buffer->font, glyphs);
diff --git a/pango/pango-types.h b/pango/pango-types.h
index 6a9ef191..59ecac0c 100644
--- a/pango/pango-types.h
+++ b/pango/pango-types.h
@@ -53,6 +53,8 @@ typedef guint32 PangoGlyph;
  * That's unlikely to matter for practical use and the expression is much
  * more compact and faster than alternatives that work exactly for both
  * integers and floating point.
+ *
+ * PANGO_PIXELS also behaves differently for +512 and -512.
  */
 
 int    pango_units_from_double (double d) G_GNUC_CONST;
diff --git a/pango/pangofc-font.c b/pango/pangofc-font.c
index 175c104c..dec1f680 100644
--- a/pango/pangofc-font.c
+++ b/pango/pangofc-font.c
@@ -723,6 +723,7 @@ pango_fc_font_kern_glyphs (PangoFcFont      *font,
   FT_Error error;
   FT_Vector kerning;
   int i;
+  gboolean hinting = font->is_hinted;
 
   g_return_if_fail (PANGO_IS_FC_FONT (font));
   g_return_if_fail (glyphs != NULL);
@@ -745,8 +746,14 @@ pango_fc_font_kern_glyphs (PangoFcFont      *font,
 			      ft_kerning_default,
 			      &kerning);
 
-      if (error == FT_Err_Ok)
-	glyphs->glyphs[i-1].geometry.width += PANGO_UNITS_26_6 (kerning.x);
+      if (error == FT_Err_Ok) {
+	int adjustment = PANGO_UNITS_26_6 (kerning.x);
+
+	if (hinting)
+	  adjustment = PANGO_UNITS_ROUND (adjustment);
+
+	glyphs->glyphs[i-1].geometry.width += adjustment;
+      }
     }
 
   PANGO_FC_FONT_UNLOCK_FACE (font);
diff --git a/pango/pangofc-private.h b/pango/pangofc-private.h
index 27ad5769..09406d13 100644
--- a/pango/pangofc-private.h
+++ b/pango/pangofc-private.h
@@ -42,6 +42,9 @@ struct _PangoFcMetricsInfo
    ((d) - PANGO_SCALE_26_6 / 2) / PANGO_SCALE_26_6)
 #define PANGO_UNITS_26_6(d) (PANGO_SCALE_26_6 * (d))
 
+#define PANGO_UNITS_ROUND(d)				\
+  (((d) + (PANGO_SCALE >> 1)) & ~(PANGO_SCALE - 1))
+
 #define PANGO_FC_GRAVITY "pangogravity"
 
 void _pango_fc_font_shutdown (PangoFcFont *fcfont);