tdf#134183 PPTX: improve import of transparency in multi-step gradients

Impress core only support a single step, improve the conversion from
multi-step to single step to take transparency into account explicitly.

Once we select the widest segment, look backwards and forward if there
are other next segments which have the same RGB color, just different
transparency and include them. This helps in general, because in case a
0% or 100% transparency is mishandled, that's very visible.

(cherry picked from commit 73993fdb5d4b507694cd0edf80887d19f7e2bf9a)

Conflicts:
	oox/source/drawingml/fillproperties.cxx

Change-Id: I11d593c01a6a4b16149ce74c1408c2a39895e941
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/100287
Tested-by: Jenkins CollaboraOffice <jenkinscollaboraoffice@gmail.com>
Reviewed-by: Miklos Vajna <vmiklos@collabora.com>

3 files changed, 60 insertions, 3 deletions

diff --git a/oox/qa/unit/data/gradient-multistep-transparency.pptx b/oox/qa/unit/data/gradient-multistep-transparency.pptx
new file mode 100644
index 000000000000..83946c71b403
--- /dev/null
+++ b/oox/qa/unit/data/gradient-multistep-transparency.pptx
diff --git a/oox/qa/unit/drawingml.cxx b/oox/qa/unit/drawingml.cxx
index 39164120e94a..6b53c1770304 100644
--- a/oox/qa/unit/drawingml.cxx
+++ b/oox/qa/unit/drawingml.cxx
@@ -10,7 +10,9 @@
 #include <test/bootstrapfixture.hxx>
 #include <unotest/macros_test.hxx>
 
+#include <com/sun/star/awt/Gradient.hpp>
 #include <com/sun/star/beans/XPropertySet.hpp>
+#include <com/sun/star/container/XNamed.hpp>
 #include <com/sun/star/drawing/XDrawPagesSupplier.hpp>
 #include <com/sun/star/drawing/FillStyle.hpp>
 #include <com/sun/star/drawing/XShape.hpp>
@@ -208,6 +210,31 @@ CPPUNIT_TEST_FIXTURE(OoxDrawingmlTest, testChartDataLabelCharColor)
     CPPUNIT_ASSERT_EQUAL(static_cast<sal_Int32>(0xffffff), nCharColor);
 }
 
+CPPUNIT_TEST_FIXTURE(OoxDrawingmlTest, testGradientMultiStepTransparency)
+{
+    // Load a document with a multi-step gradient.
+    OUString aURL
+        = m_directories.getURLFromSrc(DATA_DIRECTORY) + "gradient-multistep-transparency.pptx";
+    load(aURL);
+
+    // Check the end transparency of the gradient.
+    uno::Reference<drawing::XDrawPagesSupplier> xDrawPagesSupplier(getComponent(), uno::UNO_QUERY);
+    uno::Reference<drawing::XDrawPage> xDrawPage(xDrawPagesSupplier->getDrawPages()->getByIndex(0),
+                                                 uno::UNO_QUERY);
+    uno::Reference<container::XNamed> xShape(xDrawPage->getByIndex(1), uno::UNO_QUERY);
+    CPPUNIT_ASSERT_EQUAL(OUString("Rectangle 4"), xShape->getName());
+    uno::Reference<beans::XPropertySet> xShapeProps(xShape, uno::UNO_QUERY);
+    awt::Gradient aTransparence;
+    xShapeProps->getPropertyValue("FillTransparenceGradient") >>= aTransparence;
+
+    // Without the accompanying fix in place, this test would have failed with:
+    // - Expected: 16777215 (0xffffff)
+    // - Actual  : 3487029 (0x353535)
+    // i.e. the end transparency was not 100%, but was 21%, leading to an unexpected visible line on
+    // the right of this shape.
+    CPPUNIT_ASSERT_EQUAL(static_cast<sal_Int32>(0xffffff), aTransparence.EndColor);
+}
+
 CPPUNIT_PLUGIN_IMPLEMENT();
 
 /* vim:set shiftwidth=4 softtabstop=4 expandtab: */
diff --git a/oox/source/drawingml/fillproperties.cxx b/oox/source/drawingml/fillproperties.cxx
index f963f103d2c8..ce6cb1f931e4 100644
--- a/oox/source/drawingml/fillproperties.cxx
+++ b/oox/source/drawingml/fillproperties.cxx
@@ -504,21 +504,51 @@ void FillProperties::pushToPropMap( ShapePropertyMap& rPropMap,
                         // convert DrawingML angle (in 1/60000 degrees) to API angle (in 1/10 degrees)
                         aGradient.Angle = static_cast< sal_Int16 >( (8100 - (nDmlAngle / (PER_DEGREE / 10))) % 3600 );
                         Color aStartColor, aEndColor;
+
+                        // Try to grow the widest segment backwards: if a previous segment has the same
+                        // color, just different transparency, include it.
+                        while (aWidestSegmentStart != aGradientStops.begin())
+                        {
+                            auto it = std::prev(aWidestSegmentStart);
+                            if (it->second.getColor(rGraphicHelper, nPhClr)
+                                != aWidestSegmentStart->second.getColor(rGraphicHelper, nPhClr))
+                            {
+                                break;
+                            }
+
+                            aWidestSegmentStart = it;
+                        }
+
+                        auto aWidestSegmentEnd = std::next(aWidestSegmentStart);
+                        // Try to grow the widest segment forward: if a neext segment has the same
+                        // color, just different transparency, include it.
+                        while (aWidestSegmentEnd != std::prev(aGradientStops.end()))
+                        {
+                            auto it = std::next(aWidestSegmentEnd);
+                            if (it->second.getColor(rGraphicHelper, nPhClr)
+                                != aWidestSegmentEnd->second.getColor(rGraphicHelper, nPhClr))
+                            {
+                                break;
+                            }
+
+                            aWidestSegmentEnd = it;
+                        }
+
                         if( bSymmetric )
                         {
-                            aStartColor = std::next(aWidestSegmentStart)->second;
+                            aStartColor = aWidestSegmentEnd->second;
                             aEndColor = aWidestSegmentStart->second;
                             nBorder *= 2;
                         }
                         else if( bSwap )
                         {
-                            aStartColor = std::next(aWidestSegmentStart)->second;
+                            aStartColor = aWidestSegmentEnd->second;
                             aEndColor = aWidestSegmentStart->second;
                         }
                         else
                         {
                             aStartColor = aWidestSegmentStart->second;
-                            aEndColor = std::next(aWidestSegmentStart)->second;
+                            aEndColor = aWidestSegmentEnd->second;
                         }
 
                         SAL_INFO("oox.drawingml.gradient", "start color: " << std::hex << sal_Int32(aStartColor.getColor( rGraphicHelper, nPhClr )) << std::dec <<