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, 6 insertions, 3 deletions

diff --git a/vcl/source/gdi/salgdilayout.cxx b/vcl/source/gdi/salgdilayout.cxx
index d019b93e816b..adf26d97d9ac 100644
--- a/vcl/source/gdi/salgdilayout.cxx
+++ b/vcl/source/gdi/salgdilayout.cxx
@@ -28,6 +28,7 @@
 #include <basegfx/matrix/b2dhommatrix.hxx>
 #include <basegfx/matrix/b2dhommatrixtools.hxx>
 #include <FileDefinitionWidgetDraw.hxx>
+#include <rtl/math.hxx>
 
 // The only common SalFrame method
 
@@ -87,7 +88,8 @@ bool SalGraphics::drawTransformedBitmap(
     const basegfx::B2DPoint& /* rX */,
     const basegfx::B2DPoint& /* rY */,
     const SalBitmap& /* rSourceBitmap */,
-    const SalBitmap* /* pAlphaBitmap */)
+    const SalBitmap* /* pAlphaBitmap */,
+    double /* fAlpha */)
 {
     // here direct support for transformed bitmaps can be implemented
     return false;
@@ -836,6 +838,7 @@ bool SalGraphics::DrawTransformedBitmap(
     const basegfx::B2DPoint& rY,
     const SalBitmap& rSourceBitmap,
     const SalBitmap* pAlphaBitmap,
+    double fAlpha,
     const OutputDevice& rOutDev)
 {
     if( (m_nLayout & SalLayoutFlags::BiDiRtl) || rOutDev.IsRTLEnabled() )
@@ -852,11 +855,11 @@ bool SalGraphics::DrawTransformedBitmap(
             basegfx::B2DPoint aX = aTranslateToMirroredBounds * rX;
             basegfx::B2DPoint aY = aTranslateToMirroredBounds * rY;
 
-            return drawTransformedBitmap(aNull, aX, aY, rSourceBitmap, pAlphaBitmap);
+            return drawTransformedBitmap(aNull, aX, aY, rSourceBitmap, pAlphaBitmap, fAlpha);
         }
     }
 
-    return drawTransformedBitmap(rNull, rX, rY, rSourceBitmap, pAlphaBitmap);
+    return drawTransformedBitmap(rNull, rX, rY, rSourceBitmap, pAlphaBitmap, fAlpha);
 }
 
 bool SalGraphics::HasFastDrawTransformedBitmap() const