bitmap: Support pre/unpre-multiplying any format

If the fast-path inplace premult conversion can't be used then it will
now fallback to unpacking the buffer into a row of guint16s and use
the generic conversion.

Reviewed-by: Robert Bragg <robert@linux.intel.com>

cogl/cogl-bitmap-conversion.c

@@ -279,7 +279,7 @@ _cogl_bitmap_premult_unpacked_span_guint16 (guint16 *data,
 }
 
 static gboolean
-_cogl_bitmap_can_premult (CoglPixelFormat format)
+_cogl_bitmap_can_fast_premult (CoglPixelFormat format)
 {
   switch (format & ~COGL_PREMULT_BIT)
     {
@@ -379,7 +379,7 @@ _cogl_bitmap_convert_into_bitmap (CoglBitmap *src_bmp,
   /* If the base format is the same then we can just copy the bitmap
      instead */
   if ((src_format & ~COGL_PREMULT_BIT) == (dst_format & ~COGL_PREMULT_BIT) &&
-      (!need_premult || _cogl_bitmap_can_premult (dst_format)))
+      (!need_premult || _cogl_bitmap_can_fast_premult (dst_format)))
     {
       if (!_cogl_bitmap_copy_subregion (src_bmp, dst_bmp,
                                         0, 0, /* src_x / src_y */
@@ -504,6 +504,7 @@ gboolean
 _cogl_bitmap_unpremult (CoglBitmap *bmp)
 {
   guint8          *p, *data;
+  guint16         *tmp_row;
   int              x,y;
   CoglPixelFormat  format;
   int              width, height;
@@ -514,20 +515,32 @@ _cogl_bitmap_unpremult (CoglBitmap *bmp)
   height = _cogl_bitmap_get_height (bmp);
   rowstride = _cogl_bitmap_get_rowstride (bmp);
 
-  /* If we can premult that implies we can un-premult too... */
-  if (!_cogl_bitmap_can_premult (format))
-    return FALSE;
-
   if ((data = _cogl_bitmap_map (bmp,
                                 COGL_BUFFER_ACCESS_READ |
                                 COGL_BUFFER_ACCESS_WRITE,
                                 0)) == NULL)
     return FALSE;
 
+  /* If we can't directly unpremult the data inline then we'll
+     allocate a temporary row and unpack the data. This assumes if we
+     can fast premult then we can also fast unpremult */
+  if (_cogl_bitmap_can_fast_premult (format))
+    tmp_row = NULL;
+  else
+    tmp_row = g_malloc (sizeof (guint16) * 4 * width);
+
   for (y = 0; y < height; y++)
     {
       p = (guint8*) data + y * rowstride;
 
+      if (tmp_row)
+        {
+          _cogl_unpack_guint16 (format, p, tmp_row, width);
+          _cogl_bitmap_unpremult_unpacked_span_guint16 (tmp_row, width);
+          _cogl_pack_guint16 (format, tmp_row, p, width);
+        }
+      else
+        {
           if (format & COGL_AFIRST_BIT)
             {
               for (x = 0; x < width; x++)
@@ -542,6 +555,9 @@ _cogl_bitmap_unpremult (CoglBitmap *bmp)
           else
             _cogl_bitmap_unpremult_unpacked_span_guint8 (p, width);
         }
+    }
+
+  g_free (tmp_row);
 
   _cogl_bitmap_unmap (bmp);
 
@@ -554,6 +570,7 @@ gboolean
 _cogl_bitmap_premult (CoglBitmap *bmp)
 {
   guint8          *p, *data;
+  guint16         *tmp_row;
   int              x,y;
   CoglPixelFormat  format;
   int              width, height;
@@ -564,20 +581,31 @@ _cogl_bitmap_premult (CoglBitmap *bmp)
   height = _cogl_bitmap_get_height (bmp);
   rowstride = _cogl_bitmap_get_rowstride (bmp);
 
-  /* Make sure format supported for un-premultiplication */
-  if (!_cogl_bitmap_can_premult (format))
-    return FALSE;
-
   if ((data = _cogl_bitmap_map (bmp,
                                 COGL_BUFFER_ACCESS_READ |
                                 COGL_BUFFER_ACCESS_WRITE,
                                 0)) == NULL)
     return FALSE;
 
+  /* If we can't directly premult the data inline then we'll allocate
+     a temporary row and unpack the data. */
+  if (_cogl_bitmap_can_fast_premult (format))
+    tmp_row = NULL;
+  else
+    tmp_row = g_malloc (sizeof (guint16) * 4 * width);
+
   for (y = 0; y < height; y++)
     {
       p = (guint8*) data + y * rowstride;
 
+      if (tmp_row)
+        {
+          _cogl_unpack_guint16 (format, p, tmp_row, width);
+          _cogl_bitmap_premult_unpacked_span_guint16 (tmp_row, width);
+          _cogl_pack_guint16 (format, tmp_row, p, width);
+        }
+      else
+        {
           if (format & COGL_AFIRST_BIT)
             {
               for (x = 0; x < width; x++)
@@ -589,6 +617,9 @@ _cogl_bitmap_premult (CoglBitmap *bmp)
           else
             _cogl_bitmap_premult_unpacked_span_guint8 (p, width);
         }
+    }
+
+  g_free (tmp_row);
 
   _cogl_bitmap_unmap (bmp);