add additional 0-1 alpha argument to DrawTransformedBitmap()

This allows the VCL backends the apply the extra alpha transformation
as it sees fit, rather than it being done manually elsewhere (and
even if the backend doesn't implement it, at least do it in one
place in the function).
With the document from tdf#136223, going from slide 2 to slide 3,
this easily saves 10-30% of CPU cycles. As an additional bonus,
using AlphaMask::BlendWith() rather than AlphaMask::Replace()
makes edges of shapes noticeably more smooth.

Change-Id: I036dc9b887d6def0c7cdad3982becabdc7cd5206
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/111247
Tested-by: Jenkins
Reviewed-by: Luboš Luňák <l.lunak@collabora.com>

1 files changed, 3 insertions, 1 deletions

diff --git a/vcl/qt5/Qt5Graphics_GDI.cxx b/vcl/qt5/Qt5Graphics_GDI.cxx
index fbcc3d32d0d9..fabed0b3047b 100644
--- a/vcl/qt5/Qt5Graphics_GDI.cxx
+++ b/vcl/qt5/Qt5Graphics_GDI.cxx
@@ -626,8 +626,10 @@ bool Qt5Graphics::drawAlphaBitmap(const SalTwoRect& rPosAry, const SalBitmap& rS
 
 bool Qt5Graphics::drawTransformedBitmap(const basegfx::B2DPoint& rNull, const basegfx::B2DPoint& rX,
                                         const basegfx::B2DPoint& rY, const SalBitmap& rSourceBitmap,
-                                        const SalBitmap* pAlphaBitmap)
+                                        const SalBitmap* pAlphaBitmap, double fAlpha)
 {
+    if (fAlpha != 1.0)
+        return false;
     QImage aImage;
     if (pAlphaBitmap && !getAlphaImage(rSourceBitmap, *pAlphaBitmap, aImage))
         return false;