[freetype2] master 78b0140: [base] Improve kerning tracing and documentation.

[Werner LEMBERG]

branch: master
commit 78b014031d626a57a087c5e60447705fa834b79d
Author: Werner Lemberg <address@hidden>
Commit: Werner Lemberg <address@hidden>

    [base] Improve kerning tracing and documentation.
    
    * src/base/ftobjs.c (FT_Get_Kerning): Emit tracing message if
    scaled-down kerning values differ.
---
 ChangeLog                   |    7 +++++++
 include/freetype/freetype.h |    5 +++++
 src/base/ftobjs.c           |   23 +++++++++++++++++++++--
 3 files changed, 33 insertions(+), 2 deletions(-)

diff --git a/ChangeLog b/ChangeLog
index 2fa7140..49db8b0 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,10 @@
+2015-08-25  Werner Lemberg  <address@hidden>
+
+       [base] Improve kerning tracing and documentation.
+
+       * src/base/ftobjs.c (FT_Get_Kerning): Emit tracing message if
+       scaled-down kerning values differ.
+
 2015-08-18  Werner Lemberg  <address@hidden>
 
        [raster] Remove last remnants of `raster5' driver.
diff --git a/include/freetype/freetype.h b/include/freetype/freetype.h
index f3a9d6f..61b6a45 100644
--- a/include/freetype/freetype.h
+++ b/include/freetype/freetype.h
@@ -3041,6 +3041,11 @@ FT_BEGIN_HEADER
   /*    FT_KERNING_UNSCALED :: Return the kerning vector in original font  */
   /*                           units.                                      */
   /*                                                                       */
+  /* <Note>                                                                */
+  /*    FT_KERNING_DEFAULT returns full pixel values; it also makes        */
+  /*    FreeType heuristically scale down kerning distances at small ppem  */
+  /*    values so that they don't become too big.                          */
+  /*                                                                       */
   typedef enum  FT_Kerning_Mode_
   {
     FT_KERNING_DEFAULT  = 0,
diff --git a/src/base/ftobjs.c b/src/base/ftobjs.c
index 926ac0a..7092856 100644
--- a/src/base/ftobjs.c
+++ b/src/base/ftobjs.c
@@ -3073,18 +3073,37 @@
 
           if ( kern_mode != FT_KERNING_UNFITTED )
           {
+            FT_Pos  orig_x = akerning->x;
+            FT_Pos  orig_y = akerning->y;
+
+
             /* we scale down kerning values for small ppem values */
             /* to avoid that rounding makes them too big.         */
             /* `25' has been determined heuristically.            */
             if ( face->size->metrics.x_ppem < 25 )
-              akerning->x = FT_MulDiv( akerning->x,
+              akerning->x = FT_MulDiv( orig_x,
                                        face->size->metrics.x_ppem, 25 );
             if ( face->size->metrics.y_ppem < 25 )
-              akerning->y = FT_MulDiv( akerning->y,
+              akerning->y = FT_MulDiv( orig_y,
                                        face->size->metrics.y_ppem, 25 );
 
             akerning->x = FT_PIX_ROUND( akerning->x );
             akerning->y = FT_PIX_ROUND( akerning->y );
+
+#ifdef FT_DEBUG_LEVEL_TRACE
+            {
+              FT_Pos  orig_x_rounded = FT_PIX_ROUND( orig_x );
+              FT_Pos  orig_y_rounded = FT_PIX_ROUND( orig_y );
+
+
+              if ( akerning->x != orig_x_rounded ||
+                   akerning->y != orig_y_rounded )
+                FT_TRACE5(( "FT_Get_Kerning: horizontal kerning"
+                            " (%d, %d) scaled down to (%d, %d) pixels\n",
+                            orig_x_rounded / 64, orig_y_rounded / 64,
+                            akerning->x / 64, akerning->y / 64 ));
+            }
+#endif
           }
         }
       }