tools::Polygon::Clip() is broken with bezier curves (tdf#137068)

It preserves the points, but not the flags. Work this around
by temporarily converting to B2DPolygon, where it works.

Change-Id: I120264fbc4c7c508386f23a06435891199565aae
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/106188
Tested-by: Jenkins
Reviewed-by: Luboš Luňák <l.lunak@collabora.com>

include/tools/poly.hxx

@@ -262,6 +262,36 @@ public:
      explicit PolyPolygon(const ::basegfx::B2DPolyPolygon& rPolyPolygon);
 };
 
+template< typename charT, typename traits >
+inline std::basic_ostream<charT, traits> & operator <<(
+    std::basic_ostream<charT, traits> & stream, const Polygon& poly )
+{
+    stream << "<" << poly.GetSize() << ":";
+    for (sal_uInt16 i = 0; i < poly.GetSize(); i++)
+    {
+        if (i > 0)
+            stream << "--";
+        stream << poly.GetPoint(i);
+    }
+    stream << ">";
+    return stream;
+}
+
+template< typename charT, typename traits >
+inline std::basic_ostream<charT, traits> & operator <<(
+    std::basic_ostream<charT, traits> & stream, const PolyPolygon& poly )
+{
+    stream << "[" << poly.Count() << ":";
+    for (sal_uInt16 i = 0; i < poly.Count(); i++)
+    {
+        if (i > 0)
+            stream << ",";
+        stream << poly.GetObject(i);
+    }
+    stream << "]";
+    return stream;
+}
+
 } /* namespace tools */
 
 typedef std::vector< tools::PolyPolygon > PolyPolyVector;

tools/CppunitTest_tools_test.mk

@@ -21,6 +21,7 @@ $(eval $(call gb_CppunitTest_add_exception_objects,tools_test, \
     tools/qa/cppunit/test_inetmime \
     tools/qa/cppunit/test_json_writer \
     tools/qa/cppunit/test_pathutils \
+    tools/qa/cppunit/test_poly \
     tools/qa/cppunit/test_reversemap \
     tools/qa/cppunit/test_stream \
     tools/qa/cppunit/test_urlobj \

tools/qa/cppunit/test_poly.cxx

@@ -0,0 +1,54 @@
+/* -*- 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 <cppunit/TestFixture.h>
+#include <cppunit/extensions/HelperMacros.h>
+
+#include <tools/poly.hxx>
+
+namespace
+{
+class Test : public CppUnit::TestFixture
+{
+public:
+    void testTdf137068();
+
+    CPPUNIT_TEST_SUITE(Test);
+    CPPUNIT_TEST(testTdf137068);
+    CPPUNIT_TEST_SUITE_END();
+};
+
+void Test::testTdf137068()
+{
+    // Make sure PolyPolygon::Clip() does not break bezier curves.
+    const Point points[] = { { 1337, 411 }, { 1337, 471 }, { 1313, 530 }, { 1268, 582 } };
+    const PolyFlags flags[]
+        = { PolyFlags::Normal, PolyFlags::Control, PolyFlags::Control, PolyFlags::Normal };
+    tools::Polygon polygon(4, points, flags);
+    tools::PolyPolygon polyPolygon(polygon);
+    polyPolygon.Clip(tools::Rectangle(Point(0, 0), Size(1920, 1080)));
+    // operator== is stupid and just compares pointers, compare data manually
+    CPPUNIT_ASSERT_EQUAL(static_cast<sal_uInt16>(1), polyPolygon.Count());
+    tools::Polygon result = polyPolygon.GetObject(0);
+    CPPUNIT_ASSERT_EQUAL(static_cast<sal_uInt16>(4), result.GetSize());
+    CPPUNIT_ASSERT_EQUAL(points[0], result.GetPoint(0));
+    CPPUNIT_ASSERT_EQUAL(points[1], result.GetPoint(1));
+    CPPUNIT_ASSERT_EQUAL(points[2], result.GetPoint(2));
+    CPPUNIT_ASSERT_EQUAL(points[3], result.GetPoint(3));
+    CPPUNIT_ASSERT_EQUAL(flags[0], result.GetFlags(0));
+    CPPUNIT_ASSERT_EQUAL(flags[1], result.GetFlags(1));
+    CPPUNIT_ASSERT_EQUAL(flags[2], result.GetFlags(2));
+    CPPUNIT_ASSERT_EQUAL(flags[3], result.GetFlags(3));
+}
+
+CPPUNIT_TEST_SUITE_REGISTRATION(Test);
+}
+
+/* vim:set shiftwidth=4 softtabstop=4 expandtab: */

tools/source/generic/poly.cxx

@@ -1425,6 +1425,10 @@ void Polygon::Rotate( const Point& rCenter, double fSin, double fCos )
 
 void Polygon::Clip( const tools::Rectangle& rRect )
 {
+    // This algorithm is broken for bezier curves, they would get converted to lines.
+    // Use PolyPolygon::Clip().
+    assert( !HasFlags());
+
     // #105251# Justify rect before edge filtering
     tools::Rectangle               aJustifiedRect( rRect );
     aJustifiedRect.Justify();

tools/source/generic/poly2.cxx

@@ -27,6 +27,7 @@
 #include <tools/gen.hxx>
 #include <basegfx/polygon/b2dpolypolygon.hxx>
 #include <basegfx/polygon/b2dpolypolygoncutter.hxx>
+#include <basegfx/polygon/b2dpolygonclipper.hxx>
 
 namespace tools {
 
@@ -280,6 +281,27 @@ void PolyPolygon::Clip( const tools::Rectangle& rRect )
     if ( !nPolyCount )
         return;
 
+    // If there are bezier curves involved, Polygon::Clip() is broken.
+    // Use a temporary B2DPolyPolygon for the clipping.
+    for ( i = 0; i < nPolyCount; i++ )
+    {
+        if(mpImplPolyPolygon->mvPolyAry[i].HasFlags())
+        {
+            const basegfx::B2DPolyPolygon aPoly(
+                basegfx::utils::clipPolyPolygonOnRange(
+                    getB2DPolyPolygon(),
+                    basegfx::B2DRange(
+                        rRect.Left(),
+                        rRect.Top(),
+                        rRect.Right() + 1,
+                        rRect.Bottom() + 1),
+                    true,
+                    false));
+            *this = PolyPolygon( aPoly );
+            return;
+        }
+    }
+
     // Clip every polygon, deleting the empty ones
     for ( i = 0; i < nPolyCount; i++ )
         mpImplPolyPolygon->mvPolyAry[i].Clip( rRect );