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, 1 insertions, 1 deletions

diff --git a/vcl/inc/skia/gdiimpl.hxx b/vcl/inc/skia/gdiimpl.hxx
index 53a9a0ae0978..64707e35d134 100644
--- a/vcl/inc/skia/gdiimpl.hxx
+++ b/vcl/inc/skia/gdiimpl.hxx
@@ -174,7 +174,7 @@ public:
     /** draw transformed bitmap (maybe with alpha) where Null, X, Y define the coordinate system */
     virtual bool drawTransformedBitmap(const basegfx::B2DPoint& rNull, const basegfx::B2DPoint& rX,
                                        const basegfx::B2DPoint& rY, const SalBitmap& rSourceBitmap,
-                                       const SalBitmap* pAlphaBitmap) override;
+                                       const SalBitmap* pAlphaBitmap, double fAlpha) override;
 
     virtual bool hasFastDrawTransformedBitmap() const override;