[Impeller] Add Rect::Project

impeller/geometry/geometry_unittests.cc

@@ -2115,6 +2115,48 @@ TEST(GeometryTest, RectGetPositive) {
   }
 }
 
+TEST(GeometryTest, RectScale) {
+  {
+    auto r = Rect::MakeLTRB(-100, -100, 100, 100);
+    auto actual = r.Scale(0);
+    auto expected = Rect::MakeLTRB(0, 0, 0, 0);
+    ASSERT_RECT_NEAR(expected, actual);
+  }
+  {
+    auto r = Rect::MakeLTRB(-100, -100, 100, 100);
+    auto actual = r.Scale(-2);
+    auto expected = Rect::MakeLTRB(200, 200, -200, -200);
+    ASSERT_RECT_NEAR(expected, actual);
+  }
+  {
+    auto r = Rect::MakeLTRB(-100, -100, 100, 100);
+    auto actual = r.Scale(Point{0, 0});
+    auto expected = Rect::MakeLTRB(0, 0, 0, 0);
+    ASSERT_RECT_NEAR(expected, actual);
+  }
+  {
+    auto r = Rect::MakeLTRB(-100, -100, 100, 100);
+    auto actual = r.Scale(Size{-1, -2});
+    auto expected = Rect::MakeLTRB(100, 200, -100, -200);
+    ASSERT_RECT_NEAR(expected, actual);
+  }
+}
+
+TEST(GeometryTest, RectProject) {
+  {
+    auto r = Rect::MakeLTRB(-100, -100, 100, 100);
+    auto actual = r.Project(r);
+    auto expected = Rect::MakeLTRB(0, 0, 1, 1);
+    ASSERT_RECT_NEAR(expected, actual);
+  }
+  {
+    auto r = Rect::MakeLTRB(-100, -100, 100, 100);
+    auto actual = r.Project(Rect::MakeLTRB(0, 0, 100, 100));
+    auto expected = Rect::MakeLTRB(0.5, 0.5, 1, 1);
+    ASSERT_RECT_NEAR(expected, actual);
+  }
+}
+
 TEST(GeometryTest, CubicPathComponentPolylineDoesNotIncludePointOne) {
   CubicPathComponent component({10, 10}, {20, 35}, {35, 20}, {40, 40});
   auto polyline = component.CreatePolyline(1.0f);

impeller/geometry/rect.h

@@ -94,10 +94,7 @@ struct TRect {
                  {size.width - r.size.width, size.height - r.size.height});
   }
 
-  constexpr TRect operator*(Type scale) const {
-    return TRect({origin.x * scale, origin.y * scale},
-                 {size.width * scale, size.height * scale});
-  }
+  constexpr TRect operator*(Type scale) const { return Scale(scale); }
 
   constexpr TRect operator*(const TRect& r) const {
     return TRect({origin.x * r.origin.x, origin.y * r.origin.y},
@@ -108,6 +105,20 @@ struct TRect {
     return origin == r.origin && size == r.size;
   }
 
+  constexpr TRect Scale(Type scale) const {
+    return TRect({origin.x * scale, origin.y * scale},
+                 {size.width * scale, size.height * scale});
+  }
+
+  constexpr TRect Scale(TPoint<T> scale) const {
+    return TRect({origin.x * scale.x, origin.y * scale.y},
+                 {size.width * scale.x, size.height * scale.y});
+  }
+
+  constexpr TRect Scale(TSize<T> scale) const {
+    return Scale(TPoint<T>(scale));
+  }
+
   constexpr bool Contains(const TPoint<Type>& p) const {
     return p.x >= GetLeft() && p.x < GetRight() && p.y >= GetTop() &&
            p.y < GetBottom();
@@ -255,7 +266,7 @@ struct TRect {
 
   /// @brief  Returns a rectangle with expanded edges. Negative expansion
   ///         results in shrinking.
-  constexpr TRect<T> Expand(T left, T top, T right, T bottom) {
+  constexpr TRect<T> Expand(T left, T top, T right, T bottom) const {
     return TRect(origin.x - left,            //
                  origin.y - top,             //
                  size.width + left + right,  //
@@ -264,12 +275,22 @@ struct TRect {
 
   /// @brief  Returns a rectangle with expanded edges in all directions.
   ///         Negative expansion results in shrinking.
-  constexpr TRect<T> Expand(T amount) {
+  constexpr TRect<T> Expand(T amount) const {
     return TRect(origin.x - amount,        //
                  origin.y - amount,        //
                  size.width + amount * 2,  //
                  size.height + amount * 2);
   }
+
+  /// @brief  Returns a new rectangle that represents the projection of the
+  ///         source rectangle onto this rectangle. In other words, the source
+  ///         rectangle is redefined in terms of the corrdinate space of this
+  ///         rectangle.
+  constexpr TRect<T> Project(TRect<T> source) const {
+    return source.Shift(-origin).Scale(
+        TSize<T>(1.0 / static_cast<Scalar>(size.width),
+                 1.0 / static_cast<Scalar>(size.height)));
+  }
 };
 
 using Rect = TRect<Scalar>;