Add class for comparing angles to points in a clockwise fashion

src/core/geometry/qgsinternalgeometryengine.cpp

@@ -711,6 +711,7 @@ QgsGeometry QgsInternalGeometryEngine::densifyByDistance( double distance ) cons
   }
 }
 
+///@cond PRIVATE
 //
 // QgsLineSegmentDistanceComparer
 //
@@ -764,6 +765,45 @@ bool QgsLineSegmentDistanceComparer::operator()( QgsLineSegment2D ab, QgsLineSeg
   }
 }
 
+//
+// QgsClockwiseAngleComparer
+//
+
+bool QgsClockwiseAngleComparer::operator()( const QgsPointXY &a, const QgsPointXY &b ) const
+{
+  const bool aIsLeft = a.x() < mVertex.x();
+  const bool bIsLeft = b.x() < mVertex.x();
+  if ( aIsLeft != bIsLeft )
+    return bIsLeft;
+
+  if ( qgsDoubleNear( a.x(), mVertex.x() ) && qgsDoubleNear( b.x(), mVertex.x() ) )
+  {
+    if ( a.y() >= mVertex.y() || b.y() >= mVertex.y() )
+    {
+      return b.y() < a.y();
+    }
+    else
+    {
+      return a.y() < b.y();
+    }
+  }
+  else
+  {
+    const QgsVector oa = a - mVertex;
+    const QgsVector ob = b - mVertex;
+    const double det = oa.crossProduct( ob );
+    if ( qgsDoubleNear( det, 0.0 ) )
+    {
+      return oa.lengthSquared() < ob.lengthSquared();
+    }
+    else
+    {
+      return det < 0;
+    }
+  }
+}
+
+///@endcond PRIVATE
 
 //
 // QgsRay2D

src/core/geometry/qgsinternalgeometryengine.h

@@ -149,6 +149,8 @@ class CORE_EXPORT QgsRay2D
  * Assumes: (1) the line segments are intersected by some ray from the origin
  *          (2) the line segments do not intersect except at their endpoints
  *          (3) no line segment is collinear with the origin
+ * \ingroup core
+ * \since QGIS 3.2
  */
 class CORE_EXPORT QgsLineSegmentDistanceComparer
 {
@@ -177,6 +179,29 @@ class CORE_EXPORT QgsLineSegmentDistanceComparer
 
 };
 
+
+// adapted for QGIS geometry classes from original work at https://github.com/trylock/visibility by trylock
+
+/**
+ * Compares angles from an origin to points clockwise, starting at the positive y-axis.
+ * \ingroup core
+ * \since QGIS 3.2
+ */
+class CORE_EXPORT QgsClockwiseAngleComparer
+{
+  public:
+    explicit QgsClockwiseAngleComparer( const QgsPointXY &origin )
+      : mVertex( origin )
+    {}
+
+    bool operator()( const QgsPointXY &a, const QgsPointXY &b ) const;
+
+  private:
+
+    QgsPointXY mVertex;
+
+};
+
 ///@endcond PRIVATE
 
 #endif // QGSINTERNALGEOMETRYENGINE_H

tests/src/core/testqgsinternalgeometryengine.cpp

@@ -30,7 +30,9 @@ class TestQgsInternalGeometryEngine : public QObject
     void init();// will be called before each testfunction is executed.
     void cleanup();// will be called after every testfunction.
     void ray();
-    void lineSegmentDistanceComparer();
+    void testLineSegmentDistanceComparer_data();
+    void testLineSegmentDistanceComparer();
+    void clockwiseAngleComparer();
 
 };
 
@@ -94,24 +96,69 @@ void TestQgsInternalGeometryEngine::ray()
   QCOMPARE( intersect.x(), 2.0 );
   QCOMPARE( intersect.y(), 6.0 );
 
+  ray = QgsRay2D( QgsPointXY( 0, 0 ), QgsVector( 1, 0 ) );
+  QVERIFY( !ray.intersects( QgsLineSegment2D( QgsPointXY( -1, 1 ), QgsPointXY( -1, -1 ) ), intersect ) );
+  QVERIFY( !ray.intersects( QgsLineSegment2D( QgsPointXY( -1e-3, 1 ), QgsPointXY( -1e-3, -1 ) ), intersect ) );
+  QVERIFY( !ray.intersects( QgsLineSegment2D( QgsPointXY( -2, 0 ), QgsPointXY( -1, 0 ) ), intersect ) );
+  QVERIFY( ray.intersects( QgsLineSegment2D( QgsPointXY( 0, 1 ), QgsPointXY( 0, -1 ) ), intersect ) );
+  QCOMPARE( intersect.x(), 0.0 );
+  QCOMPARE( intersect.y(), 0.0 );
+  QVERIFY( ray.intersects( QgsLineSegment2D( QgsPointXY( -1, 0 ), QgsPointXY( 0, 0 ) ), intersect ) );
+  QCOMPARE( intersect.x(), 0.0 );
+  QCOMPARE( intersect.y(), 0.0 );
+  QVERIFY( ray.intersects( QgsLineSegment2D( QgsPointXY( 0, 0 ), QgsPointXY( -1, 0 ) ), intersect ) );
+  QCOMPARE( intersect.x(), 0.0 );
+  QCOMPARE( intersect.y(), 0.0 );
+  QVERIFY( ray.intersects( QgsLineSegment2D( QgsPointXY( 2, 1 ), QgsPointXY( 2, -1 ) ), intersect ) );
+  QCOMPARE( intersect.x(), 2.0 );
+  QCOMPARE( intersect.y(), 0.0 );
+  QVERIFY( ray.intersects( QgsLineSegment2D( QgsPointXY( 2, 0 ), QgsPointXY( 3, 0 ) ), intersect ) );
+  QCOMPARE( intersect.x(), 2.0 );
+  QCOMPARE( intersect.y(), 0.0 );
+  QVERIFY( ray.intersects( QgsLineSegment2D( QgsPointXY( 3, 0 ), QgsPointXY( 2, 0 ) ), intersect ) );
+  QCOMPARE( intersect.x(), 2.0 );
+  QCOMPARE( intersect.y(), 0.0 );
+  QVERIFY( ray.intersects( QgsLineSegment2D( QgsPointXY( 1, 0 ), QgsPointXY( 1, -1 ) ), intersect ) );
+  QCOMPARE( intersect.x(), 1.0 );
+  QCOMPARE( intersect.y(), 0.0 );
 }
 
-void TestQgsInternalGeometryEngine::lineSegmentDistanceComparer()
+void TestQgsInternalGeometryEngine::testLineSegmentDistanceComparer_data()
 {
+  QTest::addColumn<QgsPointXY>( "origin" );
+  QTest::addColumn<QgsPointXY>( "a" );
+  QTest::addColumn<QgsPointXY>( "b" );
+  QTest::addColumn<QgsPointXY>( "c" );
+  QTest::addColumn<QgsPointXY>( "d" );
+
+  QTest::newRow( "a" ) << QgsPointXY( 3, 5 ) << QgsPointXY( 1, 2 ) << QgsPointXY( 3, 4 ) << QgsPointXY( 11, 2 ) << QgsPointXY( 13, 4 );
+  QTest::newRow( "b" ) << QgsPointXY( 0, 0 ) << QgsPointXY( 1, 1 ) << QgsPointXY( 1, -1 ) << QgsPointXY( 2, 1 ) << QgsPointXY( 2, -1 );
+  QTest::newRow( "b" ) << QgsPointXY( 0, 0 ) << QgsPointXY( 1, 1 ) << QgsPointXY( 1, -1 ) << QgsPointXY( 2, 2 ) << QgsPointXY( 2, 3 );
+  QTest::newRow( "b" ) << QgsPointXY( 0, 0 ) << QgsPointXY( 2, 0 ) << QgsPointXY( 1, 1 ) << QgsPointXY( 2, 1 ) << QgsPointXY( 2, 0 );
+  QTest::newRow( "b" ) << QgsPointXY( 0, 0 ) << QgsPointXY( 2, 1 ) << QgsPointXY( 2, 0 ) << QgsPointXY( 2, 0 ) << QgsPointXY( 3, 1 );
+}
+
+void TestQgsInternalGeometryEngine::testLineSegmentDistanceComparer()
+{
+  QFETCH( QgsPointXY, origin );
+  QFETCH( QgsPointXY, a );
+  QFETCH( QgsPointXY, b );
+  QFETCH( QgsPointXY, c );
+  QFETCH( QgsPointXY, d );
+
+  QgsLineSegmentDistanceComparer cmp( origin );
+  QVERIFY( cmp( QgsLineSegment2D( a, b ), QgsLineSegment2D( c, d ) ) );
+  QVERIFY( cmp( QgsLineSegment2D( b, a ), QgsLineSegment2D( c, d ) ) );
+  QVERIFY( cmp( QgsLineSegment2D( a, b ), QgsLineSegment2D( d, c ) ) );
+  QVERIFY( cmp( QgsLineSegment2D( b, a ), QgsLineSegment2D( d, c ) ) );
+
+  QVERIFY( !cmp( QgsLineSegment2D( c, d ), QgsLineSegment2D( a, b ) ) );
+  QVERIFY( !cmp( QgsLineSegment2D( d, c ), QgsLineSegment2D( a, b ) ) );
+  QVERIFY( !cmp( QgsLineSegment2D( c, d ), QgsLineSegment2D( b, a ) ) );
+  QVERIFY( !cmp( QgsLineSegment2D( d, c ), QgsLineSegment2D( b, a ) ) );
+
   QgsLineSegmentDistanceComparer comp( QgsPointXY( 3, 5 ) );
 
-  QVERIFY( comp( QgsLineSegment2D( QgsPointXY( 1, 2 ), QgsPointXY( 3, 4 ) ),
-                 QgsLineSegment2D( QgsPointXY( 11, 2 ), QgsPointXY( 13, 4 ) ) ) );
-  QVERIFY( comp( QgsLineSegment2D( QgsPointXY( 1, 2 ), QgsPointXY( 3, 4 ) ),
-                 QgsLineSegment2D( QgsPointXY( 13, 4 ), QgsPointXY( 11, 2 ) ) ) );
-  QVERIFY( comp( QgsLineSegment2D( QgsPointXY( 1, 2 ), QgsPointXY( 3, 4 ) ),
-                 QgsLineSegment2D( QgsPointXY( -13, 4 ), QgsPointXY( -11, 2 ) ) ) );
-  QVERIFY( comp( QgsLineSegment2D( QgsPointXY( 1, 2 ), QgsPointXY( 3, 4 ) ),
-                 QgsLineSegment2D( QgsPointXY( -13, -4 ), QgsPointXY( -11, 2 ) ) ) );
-  QVERIFY( comp( QgsLineSegment2D( QgsPointXY( 1, 2 ), QgsPointXY( 3, 4 ) ),
-                 QgsLineSegment2D( QgsPointXY( 11, 2 ), QgsPointXY( 13, 4 ) ) ) );
-  QVERIFY( !comp( QgsLineSegment2D( QgsPointXY( 11, 2 ), QgsPointXY( 13, 4 ) ),
-                  QgsLineSegment2D( QgsPointXY( 1, 2 ), QgsPointXY( 3, 4 ) ) ) );
   QVERIFY( !comp( QgsLineSegment2D( QgsPointXY( 1, 2 ), QgsPointXY( 3, 4 ) ),
                   QgsLineSegment2D( QgsPointXY( 5, 6 ), QgsPointXY( 8, 9 ) ) ) );
   QVERIFY( comp( QgsLineSegment2D( QgsPointXY( 5, 6 ), QgsPointXY( 8, 9 ) ),
@@ -124,5 +171,27 @@ void TestQgsInternalGeometryEngine::lineSegmentDistanceComparer()
                  QgsLineSegment2D( QgsPointXY( 8, 9 ), QgsPointXY( 15, 16 ) ) ) );
 }
 
+void TestQgsInternalGeometryEngine::clockwiseAngleComparer()
+{
+  QgsClockwiseAngleComparer cmp( QgsPointXY( 0, 0 ) );
+  QVERIFY( cmp( QgsPointXY( 0, 1 ), QgsPointXY( 1, 1 ) ) );
+  QVERIFY( !cmp( QgsPointXY( 1, 1 ), QgsPointXY( 0, 1 ) ) );
+
+  QVERIFY( cmp( QgsPointXY( 1, 1 ), QgsPointXY( 1, -1 ) ) );
+  QVERIFY( !cmp( QgsPointXY( 1, -1 ), QgsPointXY( 1, 1 ) ) );
+
+  QVERIFY( cmp( QgsPointXY( 1, 0 ), QgsPointXY( -1, -1 ) ) );
+  QVERIFY( !cmp( QgsPointXY( -1, -1 ), QgsPointXY( 1, 0 ) ) );
+
+  QVERIFY( cmp( QgsPointXY( 0, 1 ), QgsPointXY( 0, -1 ) ) );
+  QVERIFY( !cmp( QgsPointXY( 0, -1 ), QgsPointXY( 0, 1 ) ) );
+
+  QVERIFY( cmp( QgsPointXY( 1, 0 ), QgsPointXY( 2, 0 ) ) );
+  QVERIFY( !cmp( QgsPointXY( 2, 0 ), QgsPointXY( 1, 0 ) ) );
+
+  QVERIFY( !cmp( QgsPointXY( 1, 0 ), QgsPointXY( 1, 0 ) ) );
+  QVERIFY( !cmp( QgsPointXY( 0, 0 ), QgsPointXY( 0, 0 ) ) );
+}
+
 QGSTEST_MAIN( TestQgsInternalGeometryEngine )
 #include "testqgsinternalgeometryengine.moc"