* src/base/ftbitmap.c (FT_Bitmap_Copy): Clarify the flow control.bitmap_convert

* include/freetype/ftbitmap.h (FT_Bitmap_Copy): Ditto.

2 files changed, 16 insertions, 19 deletions

diff --git a/include/freetype/ftbitmap.h b/include/freetype/ftbitmap.h
index 862b8a369..dd0e200b5 100644
--- a/include/freetype/ftbitmap.h
+++ b/include/freetype/ftbitmap.h
@@ -47,14 +47,6 @@ FT_BEGIN_HEADER
    * @description:
    *   This section contains functions for handling @FT_Bitmap objects,
    *   automatically adjusting the target's bitmap buffer size as needed.
-   *
-   *   Note that none of the functions changes the bitmap's 'flow' (as
-   *   indicated by the sign of the `pitch` field in @FT_Bitmap).
-   *
-   *   To set the flow, assign an appropriate positive or negative value to
-   *   the `pitch` field of the target @FT_Bitmap object after calling
-   *   @FT_Bitmap_Init but before calling any of the other functions
-   *   described here.
    */
 
 
@@ -105,8 +97,14 @@ FT_BEGIN_HEADER
    *   FreeType error code.  0~means success.
    *
    * @note:
-   *   `source->buffer` and `target->buffer` must neither be equal nor
-   *   overlap.
+   *   This function reallocates the memory in the target bitmap, which has
+   *   to be valid, either initialized by @FT_Bitmap_Init or reused multiple
+   *   times. `source->buffer` and `target->buffer` must neither be equal
+   *   nor overlap.  Use @FT_Bitmap_Done to finally remove the bitmap object.
+   *
+   *   The source and target bitmaps can have different flows if their
+   *   pitches are set to opposite signs before calling this function.
+   *   Otherwise, the flow is preserved.
    */
   FT_EXPORT( FT_Error )
   FT_Bitmap_Copy( FT_Library        library,
diff --git a/src/base/ftbitmap.c b/src/base/ftbitmap.c
index 53f02ae55..99afbd976 100644
--- a/src/base/ftbitmap.c
+++ b/src/base/ftbitmap.c
@@ -67,8 +67,7 @@
     FT_Memory  memory;
     FT_Error   error  = FT_Err_Ok;
     FT_Int     pitch;
-
-    FT_Int  source_pitch_sign, target_pitch_sign;
+    FT_Int     flip;
 
 
     if ( !library )
@@ -80,15 +79,15 @@
     if ( source == target )
       return FT_Err_Ok;
 
-    source_pitch_sign = source->pitch < 0 ? -1 : 1;
-    target_pitch_sign = target->pitch < 0 ? -1 : 1;
+    flip = ( source->pitch < 0 && target->pitch > 0 ) ||
+           ( source->pitch > 0 && target->pitch < 0 );
 
     memory = library->memory;
     FT_FREE( target->buffer );
 
     *target = *source;
 
-    if ( source_pitch_sign != target_pitch_sign )
+    if ( flip )
       target->pitch = -target->pitch;
 
     if ( !source->buffer )
@@ -102,10 +101,7 @@
 
     if ( !error )
     {
-      if ( source_pitch_sign == target_pitch_sign )
-        FT_MEM_COPY( target->buffer, source->buffer,
-                     (FT_Long)source->rows * pitch );
-      else
+      if ( flip )
       {
         /* take care of bitmap flow */
         FT_UInt   i;
@@ -123,6 +119,9 @@
           t -= pitch;
         }
       }
+      else
+        FT_MEM_COPY( target->buffer, source->buffer,
+                     (FT_Long)source->rows * pitch );
     }
 
     return error;