vcl: The backend should decide whether fast alpha drawing is available.

The unx drawAlphaBitmap() already already checks that the source and
destination have the same size.

Windows and OpenGL should be able to handle that without trouble.

OS X would need some additional code, so added an early return for the case
the source and result sizes do not match.

Change-Id: Ib09654aaa9c9064c232cff5094fcaa1190e931c6

vcl/quartz/salgdicommon.cxx

@@ -568,6 +568,12 @@ bool AquaSalGraphics::drawAlphaBitmap( const SalTwoRect& rTR,
 {
     DBG_DRAW_OPERATION("drawAlphaBitmap", true);
 
+    if (rTR.mnSrcWidth != rTR.mnDestWidth || rTR.mnSrcHeight != rTR.mnDestHeight)
+    {
+        // TODO - would be better to scale it by the native code
+        return false;
+    }
+
     // An image mask can't have a depth > 8 bits (should be 1 to 8 bits)
     if( rAlphaBmp.GetBitCount() > 8 )
     {

vcl/source/outdev/bitmap.cxx

@@ -524,10 +524,10 @@ void OutputDevice::DrawDeviceBitmap( const Point& rDestPt, const Size& rDestSize
 
                 if (bTryDirectPaint)
                 {
-                    // only paint direct when no scaling and no MapMode, else the
+                    // only paint direct when no MapMode, else the
                     // more expensive conversions may be done for short-time Bitmap/BitmapEx
                     // used for buffering only
-                    if (IsMapMode() || aPosAry.mnSrcWidth != aPosAry.mnDestWidth || aPosAry.mnSrcHeight != aPosAry.mnDestHeight)
+                    if (IsMapMode())
                     {
                         bTryDirectPaint = false;
                     }
@@ -663,10 +663,10 @@ void OutputDevice::DrawDeviceAlphaBitmap( const Bitmap& rBmp, const AlphaMask& r
 
         if (bTryDirectPaint)
         {
-            // only paint direct when no scaling and no MapMode, else the
+            // only paint direct when no MapMode, else the
             // more expensive conversions may be done for short-time Bitmap/BitmapEx
             // used for buffering only
-            if (IsMapMode() || rSrcSizePixel.Width() != aOutSz.Width() || rSrcSizePixel.Height() != aOutSz.Height())
+            if (IsMapMode())
             {
                 bTryDirectPaint = false;
             }

vcl/win/source/gdi/gdiimpl.cxx

@@ -774,17 +774,6 @@ void WinSalGraphicsImpl::drawBitmap( const SalTwoRect& rPosAry,
     DBG_ASSERT( !mrParent.isPrinter(), "No transparency print possible!" );
     bool bTryDirectPaint(!mrParent.isPrinter() && !mbXORMode);
 
-    if(bTryDirectPaint)
-    {
-        // only paint direct when no scaling and no MapMode, else the
-        // more expensive conversions may be done for short-time Bitmap/BitmapEx
-        // used for buffering only
-        if(rPosAry.mnSrcWidth == rPosAry.mnDestWidth && rPosAry.mnSrcHeight == rPosAry.mnDestHeight)
-        {
-            bTryDirectPaint = false;
-        }
-    }
-
     // try to draw using GdiPlus directly
     if(bTryDirectPaint && drawAlphaBitmap(rPosAry, rSSalBitmap, rSTransparentBitmap))
     {