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

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

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,
@@ -178,8 +176,8 @@ FT_BEGIN_HEADER
    *     The source bitmap.
    *
    *   alignment ::
-   *     The pitch of the bitmap is a multiple of this argument.  Common
-   *     values are 1, 2, or 4.
+   *     The pitch of the target bitmap is a multiple of this argument.
+   *     Common values are 1, 2, or 4.
    *
    * @output:
    *   target ::
@@ -189,16 +187,16 @@ FT_BEGIN_HEADER
    *   FreeType error code.  0~means success.
    *
    * @note:
-   *   It is possible to call @FT_Bitmap_Convert multiple times without
-   *   calling @FT_Bitmap_Done (the memory is simply reallocated).
+   *   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.
    *
-   *   Use @FT_Bitmap_Done to finally remove the bitmap object.
+   *   Negative alignment values produce bottom-up bitmaps with negative
+   *   pitch.  Zero alignment is treated as one, i.e., no padding is used.
    *
    *   The `library` argument is taken to have access to FreeType's memory
    *   handling functions.
-   *
-   *   `source->buffer` and `target->buffer` must neither be equal nor
-   *   overlap.
    */
   FT_EXPORT( FT_Error )
   FT_Bitmap_Convert( FT_Library        library,

src/base/ftbitmap.c

@@ -66,11 +66,8 @@
   {
     FT_Memory  memory;
     FT_Error   error  = FT_Err_Ok;
-
-    FT_Int    pitch;
-    FT_ULong  size;
-
-    FT_Int  source_pitch_sign, target_pitch_sign;
+    FT_Int     pitch;
+    FT_Int     flip;
 
 
     if ( !library )
@@ -82,53 +79,29 @@
     if ( source == target )
       return FT_Err_Ok;
 
-    source_pitch_sign = source->pitch < 0 ? -1 : 1;
-    target_pitch_sign = target->pitch < 0 ? -1 : 1;
-
-    if ( !source->buffer )
-    {
-      *target = *source;
-      if ( source_pitch_sign != target_pitch_sign )
-        target->pitch = -target->pitch;
-
-      return FT_Err_Ok;
-    }
+    flip = ( source->pitch < 0 && target->pitch > 0 ) ||
+           ( source->pitch > 0 && target->pitch < 0 );
 
     memory = library->memory;
-    pitch  = source->pitch;
+    FT_FREE( target->buffer );
 
+    *target = *source;
+
+    if ( flip )
+      target->pitch = -target->pitch;
+
+    if ( !source->buffer )
+      return FT_Err_Ok;
+
+    pitch  = source->pitch;
     if ( pitch < 0 )
       pitch = -pitch;
-    size = (FT_ULong)pitch * source->rows;
 
-    if ( target->buffer )
-    {
-      FT_Int    target_pitch = target->pitch;
-      FT_ULong  target_size;
-
-
-      if ( target_pitch < 0 )
-        target_pitch = -target_pitch;
-      target_size = (FT_ULong)target_pitch * target->rows;
-
-      if ( target_size != size )
-        FT_MEM_QREALLOC( target->buffer, target_size, size );
-    }
-    else
-      FT_MEM_QALLOC( target->buffer, size );
+    FT_MEM_QALLOC_MULT( target->buffer, target->rows, pitch );
 
     if ( !error )
     {
-      unsigned char *p;
-
-
-      p = target->buffer;
-      *target = *source;
-      target->buffer = p;
-
-      if ( source_pitch_sign == target_pitch_sign )
-        FT_MEM_COPY( target->buffer, source->buffer, size );
-      else
+      if ( flip )
       {
         /* take care of bitmap flow */
         FT_UInt   i;
@@ -146,6 +119,9 @@
           t -= pitch;
         }
       }
+      else
+        FT_MEM_COPY( target->buffer, source->buffer,
+                     (FT_Long)source->rows * pitch );
     }
 
     return error;
@@ -542,39 +518,29 @@
     case FT_PIXEL_MODE_LCD_V:
     case FT_PIXEL_MODE_BGRA:
       {
-        FT_Int    pad, old_target_pitch, target_pitch;
-        FT_ULong  old_size;
+        FT_Int  width = (FT_Int)source->width;
 
 
-        old_target_pitch = target->pitch;
-        if ( old_target_pitch < 0 )
-          old_target_pitch = -old_target_pitch;
-
-        old_size = target->rows * (FT_UInt)old_target_pitch;
+        FT_Bitmap_Done( library, target );
 
         target->pixel_mode = FT_PIXEL_MODE_GRAY;
         target->rows       = source->rows;
         target->width      = source->width;
 
-        pad = 0;
-        if ( alignment > 0 )
+        if ( alignment )
         {
-          pad = (FT_Int)source->width % alignment;
-          if ( pad != 0 )
-            pad = alignment - pad;
+          FT_Int  rem = width % alignment;
+
+
+          if ( rem )
+            width = alignment < 0 ? width - rem - alignment
+                                  : width - rem + alignment;
         }
 
-        target_pitch = (FT_Int)source->width + pad;
-
-        if ( target_pitch > 0                                               &&
-             (FT_ULong)target->rows > FT_ULONG_MAX / (FT_ULong)target_pitch )
-          return FT_THROW( Invalid_Argument );
-
-        if ( FT_QREALLOC( target->buffer,
-                          old_size, target->rows * (FT_UInt)target_pitch ) )
+        if ( FT_QALLOC_MULT( target->buffer, target->rows, width ) )
           return error;
 
-        target->pitch = target->pitch < 0 ? -target_pitch : target_pitch;
+        target->pitch = alignment < 0 ? -width : width;
       }
       break;