Add dot and cross product to Point (flutter#33)

Author: bdero

impeller/geometry/geometry_unittests.cc

@@ -454,6 +454,46 @@ TEST(GeometryTest, CanUsePointAssignmentOperators) {
   }
 }
 
+TEST(GeometryTest, PointDotProduct) {
+  {
+    Point p(1, 0);
+    Scalar s = p.Dot(Point(-1, 0));
+    ASSERT_FLOAT_EQ(s, -1);
+  }
+
+  {
+    Point p(0, -1);
+    Scalar s = p.Dot(Point(-1, 0));
+    ASSERT_FLOAT_EQ(s, 0);
+  }
+
+  {
+    Point p(1, 2);
+    Scalar s = p.Dot(Point(3, -4));
+    ASSERT_FLOAT_EQ(s, -5);
+  }
+}
+
+TEST(GeometryTest, PointCrossProduct) {
+  {
+    Point p(1, 0);
+    Scalar s = p.Cross(Point(-1, 0));
+    ASSERT_FLOAT_EQ(s, 0);
+  }
+
+  {
+    Point p(0, -1);
+    Scalar s = p.Cross(Point(-1, 0));
+    ASSERT_FLOAT_EQ(s, -1);
+  }
+
+  {
+    Point p(1, 2);
+    Scalar s = p.Cross(Point(3, -4));
+    ASSERT_FLOAT_EQ(s, -10);
+  }
+}
+
 TEST(GeometryTest, CanConvertBetweenDegressAndRadians) {
   {
     auto deg = Degrees{90.0};

impeller/geometry/point.h

@@ -175,6 +175,12 @@ struct TPoint {
     return {x / length, y / length};
   }
 
+  constexpr Scalar Cross(const TPoint& p) const {
+    return (x * p.y) - (y * p.x);
+  }
+
+  constexpr Scalar Dot(const TPoint& p) const { return (x * p.x) + (y * p.y); }
+
   constexpr bool IsZero() const { return x == 0 && y == 0; }
 };