Bug 952011 - Add gfx3DMatrix API for untransformed rects and points. r=bjacob

gfx/thebes/gfx3DMatrix.cpp

@@ -788,10 +788,9 @@ gfxRect gfx3DMatrix::ProjectRectBounds(const gfxRect& aRect) const
   gfxPoint points[4];
 
   points[0] = ProjectPoint(aRect.TopLeft());
-  points[1] = ProjectPoint(gfxPoint(aRect.X() + aRect.Width(), aRect.Y()));
+  points[1] = ProjectPoint(aRect.TopRight());
-  points[2] = ProjectPoint(gfxPoint(aRect.X(), aRect.Y() + aRect.Height()));
+  points[2] = ProjectPoint(aRect.BottomLeft());
-  points[3] = ProjectPoint(gfxPoint(aRect.X() + aRect.Width(),
+  points[3] = ProjectPoint(aRect.BottomRight());
-                                    aRect.Y() + aRect.Height()));
 
   gfxFloat min_x, max_x;
   gfxFloat min_y, max_y;
@@ -809,6 +808,27 @@ gfxRect gfx3DMatrix::ProjectRectBounds(const gfxRect& aRect) const
   return gfxRect(min_x, min_y, max_x - min_x, max_y - min_y);
 }
 
+gfxRect gfx3DMatrix::UntransformBounds(const gfxRect& aRect, const gfxRect& aChildBounds) const
+{
+  gfxRect bounds = TransformBounds(aChildBounds);
+
+  gfxRect rect = aRect.Intersect(bounds);
+
+  return Inverse().ProjectRectBounds(rect);
+}
+
+bool gfx3DMatrix::UntransformPoint(const gfxPoint& aPoint, const gfxRect& aChildBounds, gfxPoint* aOut) const
+{
+  gfxRect bounds = TransformBounds(aChildBounds);
+
+  if (!bounds.Contains(aPoint)) {
+    return false;
+  }
+
+  *aOut = Inverse().ProjectPoint(aPoint);
+  return true;
+}
+
 gfxPoint3D gfx3DMatrix::GetNormalVector() const
 {
   // Define a plane in transformed space as the transformations

gfx/thebes/gfx3DMatrix.h

@@ -250,6 +250,25 @@ public:
   gfxPoint ProjectPoint(const gfxPoint& aPoint) const;
   gfxRect ProjectRectBounds(const gfxRect& aRect) const;
 
+  /**
+   * Transforms a point by the inverse of this matrix. In the case of projective transforms, some screen
+   * points have no equivalent in the untransformed plane (if they exist past the vanishing point). To
+   * avoid this, we need to specify the bounds of the untransformed plane to restrict the search area.
+   *
+   * @param aPoint Point to untransform.
+   * @param aChildBounds Bounds of the untransformed plane.
+   * @param aOut Untransformed point.
+   * @return Returns true if a point was found within a ChildBounds, false otherwise.
+   */
+  bool UntransformPoint(const gfxPoint& aPoint, const gfxRect& aChildBounds, gfxPoint* aOut) const;
+
+
+  /**
+   * Same as UntransformPoint, but untransforms a rect and returns the bounding rect of the result.
+   * Returns an empty rect if the result doesn't intersect aChildBounds.
+   */
+  gfxRect UntransformBounds(const gfxRect& aRect, const gfxRect& aChildBounds) const;
+
 
   /**
    * Inverts this matrix, if possible. Otherwise, the matrix is left