Bug 1496194 - Add a RectAbsolute implementation for MoveInsideAndClamp. r=botond

Depends on D15135

Differential Revision: https://phabricator.services.mozilla.com/D15136

--HG--
extra : moz-landing-system : lando

gfx/2d/RectAbsolute.h

@@ -239,6 +239,30 @@ struct BaseRectAbsolute {
     left = static_cast<T>(ceil(double(left) / aXScale));
     top = static_cast<T>(ceil(double(top) / aYScale));
   }
+
+  /**
+   * Translate this rectangle to be inside aRect. If it doesn't fit inside
+   * aRect then the dimensions that don't fit will be shrunk so that they
+   * do fit. The resulting rect is returned.
+   */
+  MOZ_MUST_USE Sub MoveInsideAndClamp(const Sub& aRect) const {
+    T newLeft = std::max(aRect.left, left);
+    T newTop = std::max(aRect.top, top);
+    T width = std::min(aRect.Width(), Width());
+    T height = std::min(aRect.Height(), Height());
+    Sub rect(newLeft, newTop, newLeft + width, newTop + height);
+    newLeft = std::min(rect.right, aRect.right) - width;
+    newTop = std::min(rect.bottom, aRect.bottom) - height;
+    rect.MoveBy(newLeft - rect.left, newTop - rect.top);
+    return rect;
+  }
+
+  friend std::ostream& operator<<(
+      std::ostream& stream,
+      const BaseRectAbsolute<T, Sub, Point, Rect>& aRect) {
+    return stream << '(' << aRect.left << ',' << aRect.top << ',' << aRect.right
+                  << ',' << aRect.bottom << ')';
+  }
 };
 
 template <class Units>

gfx/tests/gtest/TestRect.cpp

@@ -599,3 +599,36 @@ TEST(Gfx, gfxRect) {
   TestSetWH<gfxRect>();
   TestSwap<gfxRect>();
 }
+
+static void TestMoveInsideAndClamp(IntRect aSrc, IntRect aTarget,
+                                   IntRect aExpected) {
+  // Test the implementation in BaseRect (x/y/width/height representation)
+  IntRect result = aSrc.MoveInsideAndClamp(aTarget);
+  EXPECT_TRUE(result.IsEqualEdges(aExpected))
+      << "Source " << aSrc << " Target " << aTarget << " Expected " << aExpected
+      << " Actual " << result;
+
+  // Also test the implementation in RectAbsolute (left/top/right/bottom
+  // representation)
+  IntRectAbsolute absSrc = IntRectAbsolute::FromRect(aSrc);
+  IntRectAbsolute absTarget = IntRectAbsolute::FromRect(aTarget);
+  IntRectAbsolute absExpected = IntRectAbsolute::FromRect(aExpected);
+
+  IntRectAbsolute absResult = absSrc.MoveInsideAndClamp(absTarget);
+  EXPECT_TRUE(absResult.IsEqualEdges(absExpected))
+      << "AbsSource " << absSrc << " AbsTarget " << absTarget << " AbsExpected "
+      << absExpected << " AbsActual " << absResult;
+}
+
+TEST(Gfx, MoveInsideAndClamp) {
+  TestMoveInsideAndClamp(IntRect(0, 0, 10, 10), IntRect(1, -1, 10, 10),
+                         IntRect(1, -1, 10, 10));
+  TestMoveInsideAndClamp(IntRect(0, 0, 10, 10), IntRect(-1, -1, 12, 5),
+                         IntRect(0, -1, 10, 5));
+  TestMoveInsideAndClamp(IntRect(0, 0, 10, 10), IntRect(10, 11, 10, 0),
+                         IntRect(10, 11, 10, 0));
+  TestMoveInsideAndClamp(IntRect(0, 0, 10, 10), IntRect(-10, -1, 10, 0),
+                         IntRect(-10, -1, 10, 0));
+  TestMoveInsideAndClamp(IntRect(0, 0, 0, 0), IntRect(10, -10, 10, 10),
+                         IntRect(10, 0, 0, 0));
+}