tdf#152997 - Duplicate an odd length dash array to meet the spec

An odd-length array will be drawn as one dash spanning the entire path.
The specifications under
https://www.w3.org/TR/svg-strokes/#StrokeDashing state: "If the list has
an odd number of values, then it is repeated to yield an even number of
values. Thus, the rendering behaviour of stroke-array: 5,4,2 is
equivalent to stroke-dasharray: 5,4,2,5,4,2."

Change-Id: I8f233c4cec5c85f5ab1096b032cbb8743715f14d
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/211062
Reviewed-by: Andreas Heinisch <andreas.heinisch@yahoo.de>
Tested-by: Jenkins

drawinglayer/CppunitTest_drawinglayer_processors.mk

@@ -37,6 +37,7 @@ $(eval $(call gb_CppunitTest_use_externals,drawinglayer_processors,\
 ))
 
 $(eval $(call gb_CppunitTest_add_exception_objects,drawinglayer_processors, \
+	drawinglayer/qa/unit/strokeattribute \
 	drawinglayer/qa/unit/vclmetafileprocessor2d \
 	drawinglayer/qa/unit/vclpixelprocessor2d \
 ))

drawinglayer/qa/unit/strokeattribute.cxx

@@ -0,0 +1,78 @@
+/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
+/*
+ * This file is part of the LibreOffice project.
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/.
+ */
+
+#include <cppunit/TestAssert.h>
+#include <test/bootstrapfixture.hxx>
+
+#include <drawinglayer/attribute/strokeattribute.hxx>
+
+using namespace drawinglayer::attribute;
+
+namespace
+{
+class StrokeAttributeTest : public test::BootstrapFixture
+{
+};
+
+CPPUNIT_TEST_FIXTURE(StrokeAttributeTest, tdf152997_odd_length_dash_array)
+{
+    std::vector<double> aDashArray{ 6.0 };
+    StrokeAttribute aStroke(std::move(aDashArray));
+
+    // Without the fix in place, this test would have failed with
+    // - Expected: 2
+    // - Actual  : 1
+    // i.e. the odd-length array was not duplicated
+    const std::vector<double> aExpected{ 6.0, 6.0 };
+    CPPUNIT_ASSERT_EQUAL(aExpected.size(), aStroke.getDotDashArray().size());
+    CPPUNIT_ASSERT_EQUAL(12.0, aStroke.getFullDotDashLen());
+    for (size_t i = 0; i < aExpected.size(); ++i)
+        CPPUNIT_ASSERT_DOUBLES_EQUAL(aExpected[i], aStroke.getDotDashArray()[i], 1E-12);
+}
+
+CPPUNIT_TEST_FIXTURE(StrokeAttributeTest, tdf152997_odd_length_dash_array_multiple_values)
+{
+    std::vector<double> aDashArray{ 5.0, 3.0, 2.0 };
+    StrokeAttribute aStroke(std::move(aDashArray));
+
+    // Without the fix in place, this test would have failed with
+    // - Expected: 6
+    // - Actual  : 3
+    // i.e. the odd-length array was not duplicated
+    const std::vector<double> aExpected{ 5.0, 3.0, 2.0, 5.0, 3.0, 2.0 };
+    CPPUNIT_ASSERT_EQUAL(aExpected.size(), aStroke.getDotDashArray().size());
+    for (size_t i = 0; i < aExpected.size(); ++i)
+        CPPUNIT_ASSERT_DOUBLES_EQUAL(aExpected[i], aStroke.getDotDashArray()[i], 1E-12);
+}
+
+CPPUNIT_TEST_FIXTURE(StrokeAttributeTest, tdf152997_even_length_dash_array)
+{
+    std::vector<double> aDashArray{ 4.0, 2.0 };
+    StrokeAttribute aStroke(std::move(aDashArray), 6.0);
+
+    // An even-length dash array should not be changed
+    const std::vector<double> aExpected{ 4.0, 2.0 };
+    CPPUNIT_ASSERT_EQUAL(aExpected.size(), aStroke.getDotDashArray().size());
+    CPPUNIT_ASSERT_EQUAL(6.0, aStroke.getFullDotDashLen());
+    for (size_t i = 0; i < aExpected.size(); ++i)
+        CPPUNIT_ASSERT_DOUBLES_EQUAL(aExpected[i], aStroke.getDotDashArray()[i], 1E-12);
+}
+
+CPPUNIT_TEST_FIXTURE(StrokeAttributeTest, tdf152997_empty_dash_array)
+{
+    std::vector<double> aDashArray;
+    StrokeAttribute aStroke(std::move(aDashArray));
+
+    // An empty dash array should not be changed
+    CPPUNIT_ASSERT(aStroke.getDotDashArray().empty());
+}
+
+} // namespace
+
+/* vim:set shiftwidth=4 softtabstop=4 expandtab: */

drawinglayer/source/attribute/strokeattribute.cxx

@@ -36,6 +36,21 @@ namespace drawinglayer::attribute
             :   maDotDashArray(std::move(rDotDashArray)),
                 mfFullDotDashLen(fFullDotDashLen)
             {
+                // tdf#152997 - duplicate an odd length dash array in order to meet the spec.
+                // An odd-length array will be drawn as one dash spanning the entire path. The
+                // specifications under https://www.w3.org/TR/svg-strokes/#StrokeDashing state:
+                // "If the list has an odd number of values, then it is repeated to yield an
+                // even number of values. Thus, the rendering behavior of stroke-dasharray: 5,3,2
+                // is equivalent to stroke-dasharray: 5,3,2,5,3,2."
+                if (maDotDashArray.size() % 2 == 1)
+                {
+                    const std::vector<double> aOriginal(maDotDashArray);
+                    maDotDashArray.insert(maDotDashArray.end(), aOriginal.begin(), aOriginal.end());
+
+                    // Increase the length accordingly
+                    if (0.0 != mfFullDotDashLen)
+                        mfFullDotDashLen *= 2.0;
+                }
             }
 
             ImpStrokeAttribute()