commit ded4b38deb2d7190ecc500250b63204b0f6d5577
author Luboš Luňák <l.lunak@collabora.com> Wed Mar 17 16:03:12 2021 +0100
committer Xisco Fauli <xiscofauli@libreoffice.org> Wed Mar 17 21:22:17 2021 +0100
tree 1e3244c0142b2f0c060cd03cc2011db2bae6cb8b
parent b3c94568e25990b1f6b3df1f7919acecdca3ffd2

round polygon points before merging them for Skia drawing (tdf#140848)

basegfx::utils::mergeToSinglePolyPolygon() appears to have rounding
problems. Point coordinates are in pixels anyway.

Change-Id: I9880cc32f934a08923a5c59278f6aa07852c05f9
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/112647
Tested-by: Jenkins
Reviewed-by: Luboš Luňák <l.lunak@collabora.com>
(cherry picked from commit ff1cfaf87ce0aa9673e1c3f92308cde6a2c6aa69)
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/112615
Reviewed-by: Xisco Fauli <xiscofauli@libreoffice.org>

vcl/qa/cppunit/skia/skia.cxx

diff --git a/vcl/qa/cppunit/skia/skia.cxx b/vcl/qa/cppunit/skia/skia.cxx
index 1f04c58..33341bf 100644
--- a/vcl/qa/cppunit/skia/skia.cxx
+++ b/vcl/qa/cppunit/skia/skia.cxx
@@ -36,6 +36,7 @@
    void testAlphaBlendWith();
    void testBitmapCopyOnWrite();
    void testTdf137329();
    void testTdf140848();

    CPPUNIT_TEST_SUITE(SkiaTest);
    CPPUNIT_TEST(testBitmapErase);
@@ -44,6 +45,7 @@
    CPPUNIT_TEST(testAlphaBlendWith);
    CPPUNIT_TEST(testBitmapCopyOnWrite);
    CPPUNIT_TEST(testTdf137329);
    CPPUNIT_TEST(testTdf140848);
    CPPUNIT_TEST_SUITE_END();

private:
@@ -326,6 +328,34 @@
    CPPUNIT_ASSERT_EQUAL(COL_BLACK, device->GetPixel(Point(4, 4)));
}

void SkiaTest::testTdf140848()
{
    if (!SkiaHelper::isVCLSkiaEnabled())
        return;
    ScopedVclPtr<VirtualDevice> device = VclPtr<VirtualDevice>::Create(DeviceFormat::DEFAULT);
    device->SetOutputSizePixel(Size(1300, 400));
    device->SetBackground(Wallpaper(COL_BLACK));
    device->SetAntialiasing(AntialiasingFlags::Enable);
    device->Erase();
    device->SetLineColor();
    device->SetFillColor(COL_WHITE);
    basegfx::B2DPolygon p1 = { { 952.73121259842514519, 102.4599685039370911 },
                               { 952.73121259842514519, 66.55445669291347599 },
                               { 1239.9753070866140661, 66.554456692913390725 },
                               { 1239.9753070866140661, 138.36548031496062094 },
                               { 952.73121259842514519, 138.36548031496070621 } };
    basegfx::B2DPolygon p2 = { { 1168.1642834645670064, 210.17650393700790801 },
                               { 1168.1642834645670064, 66.554456692913404936 },
                               { 1239.9753070866140661, 66.554456692913390725 },
                               { 1239.9753070866142934, 353.79855118110236845 },
                               { 1168.1642834645670064, 353.79855118110236845 } };
    device->DrawPolyPolygon(basegfx::B2DPolyPolygon(p1));
    device->DrawPolyPolygon(basegfx::B2DPolyPolygon(p2));
    //savePNG("/tmp/tdf140848.png", device);
    // Rounding errors caused the overlapping part not to be drawn.
    CPPUNIT_ASSERT_EQUAL(COL_WHITE, device->GetPixel(Point(1200, 100)));
}

} // namespace

CPPUNIT_TEST_SUITE_REGISTRATION(SkiaTest);

vcl/skia/gdiimpl.cxx

diff --git a/vcl/skia/gdiimpl.cxx b/vcl/skia/gdiimpl.cxx
index 4e6383d..ba9737c 100644
--- a/vcl/skia/gdiimpl.cxx
+++ b/vcl/skia/gdiimpl.cxx
@@ -1012,6 +1012,20 @@
    return true;
}

// Tdf#140848 - basegfx::utils::mergeToSinglePolyPolygon() seems to have rounding
// errors that sometimes cause it to merge incorrectly.
static void roundPolygonPoints(basegfx::B2DPolyPolygon& polyPolygon)
{
    for (basegfx::B2DPolygon& polygon : polyPolygon)
    {
        polygon.makeUnique();
        for (sal_uInt32 i = 0; i < polygon.count(); ++i)
            polygon.setB2DPoint(i, basegfx::B2DPoint(basegfx::fround(polygon.getB2DPoint(i))));
        // Control points are saved as vectors relative to points, so hopefully
        // there's no need to round those.
    }
}

void SkiaSalGraphicsImpl::checkPendingDrawing()
{
    if (mLastPolyPolygonInfo.polygons.size() != 0)
@@ -1023,10 +1037,12 @@
        if (polygons.size() == 1)
            performDrawPolyPolygon(polygons.front(), transparency, true);
        else
            // TODO: tdf#136222 shows that basegfx::utils::mergeToSinglePolyPolygon() is unreliable
            // in corner cases, possibly either a bug or rounding errors somewhere.
        {
            for (basegfx::B2DPolyPolygon& p : polygons)
                roundPolygonPoints(p);
            performDrawPolyPolygon(basegfx::utils::mergeToSinglePolyPolygon(polygons), transparency,
                                   true);
        }
    }
}