make RenderMaskPrimitive2DPixel() clip using clipping (tdf#140797)

The original implementation had this peculiar idea of implementing
clipping using transparency, which slows everything down, because
contents need to be copied and then alpha-blended. Keep that only
for when edges of the clip are to be smoothed.
As a side-effect this also seems to fix tdf#115843 again.
The commit also adjusts the test for tdf#133477 to not rely
on the rounding introduced by the optimization from tdf#115843.

Change-Id: Iebae5996159cf9f17066205985c5b591abdae105
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/111966
Tested-by: Jenkins
Reviewed-by: Luboš Luňák <l.lunak@collabora.com>
(cherry picked from commit 6b8c157a0b4f37a09fdbf656919b2df06a3abc3e)
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/112217
Reviewed-by: Xisco Fauli <xiscofauli@libreoffice.org>

2 files changed, 20 insertions, 15 deletions

diff --git a/drawinglayer/source/processor2d/vclprocessor2d.cxx b/drawinglayer/source/processor2d/vclprocessor2d.cxx
index c2c835e5291d..80c7fbdb6556 100644
--- a/drawinglayer/source/processor2d/vclprocessor2d.cxx
+++ b/drawinglayer/source/processor2d/vclprocessor2d.cxx
@@ -751,7 +751,7 @@ void VclProcessor2D::RenderPolyPolygonGraphicPrimitive2D(
     }
 }
 
-// mask group. Force output to VDev and create mask from given mask
+// mask group
 void VclProcessor2D::RenderMaskPrimitive2DPixel(const primitive2d::MaskPrimitive2D& rMaskCandidate)
 {
     if (rMaskCandidate.getChildren().empty())
@@ -763,6 +763,17 @@ void VclProcessor2D::RenderMaskPrimitive2DPixel(const primitive2d::MaskPrimitive
         return;
 
     aMask.transform(maCurrentTransformation);
+
+    // Unless smooth edges are needed, simply use clipping.
+    if (basegfx::utils::isRectangle(aMask) || !getOptionsDrawinglayer().IsAntiAliasing())
+    {
+        mpOutputDevice->Push(PushFlags::CLIPREGION);
+        mpOutputDevice->IntersectClipRegion(vcl::Region(aMask));
+        process(rMaskCandidate.getChildren());
+        mpOutputDevice->Pop();
+        return;
+    }
+
     const basegfx::B2DRange aRange(basegfx::utils::getRange(aMask));
     impBufferDevice aBufferDevice(*mpOutputDevice, aRange);
 
@@ -779,19 +790,11 @@ void VclProcessor2D::RenderMaskPrimitive2DPixel(const primitive2d::MaskPrimitive
     // back to old OutDev
     mpOutputDevice = pLastOutputDevice;
 
-    // if the mask fills the whole area we can skip
-    // creating a transparent vd and filling it.
-    if (!basegfx::utils::isRectangle(aMask))
-    {
-        // draw mask
-        // with AA, use 8bit AlphaMask to get nice borders; no AA -> use 1bit mask
-        VirtualDevice& rMask = getOptionsDrawinglayer().IsAntiAliasing()
-                                   ? aBufferDevice.getTransparence()
-                                   : aBufferDevice.getMask();
-        rMask.SetLineColor();
-        rMask.SetFillColor(COL_BLACK);
-        rMask.DrawPolyPolygon(aMask);
-    }
+    // draw mask
+    VirtualDevice& rMask = aBufferDevice.getTransparence();
+    rMask.SetLineColor();
+    rMask.SetFillColor(COL_BLACK);
+    rMask.DrawPolyPolygon(aMask);
 
     // dump buffer to outdev
     aBufferDevice.paint();
diff --git a/sw/qa/extras/uiwriter/uiwriter3.cxx b/sw/qa/extras/uiwriter/uiwriter3.cxx
index 018a96a78ee6..a2b8c8bc1c38 100644
--- a/sw/qa/extras/uiwriter/uiwriter3.cxx
+++ b/sw/qa/extras/uiwriter/uiwriter3.cxx
@@ -2086,10 +2086,12 @@ CPPUNIT_TEST_FIXTURE(SwUiWriterTest3, testTdf133477)
     aStream.Seek(STREAM_SEEK_TO_BEGIN);
 
     // Read it back and check the color of the first pixel.
+    // (Actually check at one-pixel offset, because imprecise shape positioning may
+    // result in blending with background for the first pixel).
     Graphic aGraphic;
     ReadGraphic(aStream, aGraphic);
     BitmapEx aBitmap = aGraphic.GetBitmapEx();
-    CPPUNIT_ASSERT_EQUAL(Color(0, 102, 204), aBitmap.GetPixelColor(0, 0));
+    CPPUNIT_ASSERT_EQUAL(Color(0, 102, 204), aBitmap.GetPixelColor(1, 1));
 }
 
 CPPUNIT_TEST_FIXTURE(SwUiWriterTest3, testTdf137964)