Fix matrix3d transform under page zoom

third_party/WebKit/Source/platform/transforms/TransformationMatrix.h

 /*
  * Copyright (C) 2005, 2006 Apple Computer, Inc.  All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 319 matching lines @@
   TransformationMatrix& skewY(double angle) { return skew(0, angle); }
 
   TransformationMatrix& applyPerspective(double p);
 
   // Changes the transform to apply as if the origin were at (x, y, z).
   TransformationMatrix& applyTransformOrigin(double x, double y, double z);
   TransformationMatrix& applyTransformOrigin(const FloatPoint3D& origin) {
     return applyTransformOrigin(origin.x(), origin.y(), origin.z());
   }
 
+  // Changes the transform to:
+  //
+  //     scale3d(z, z, z) * mat * scale3d(1/z, 1/z, 1/z)
+  //
+  // Useful for mapping zoomed points to their zoomed transformed result:
+  //
+  //     new_mat * (scale3d(z, z, z) * x) == scale3d(z, z, z) * (mat * x)
+  //

[alancutter (OOO until 2018), 2016/11/10 06:50:03]

Nice comment! I'd even put this in the description, it's very succinct and
clear.

+  TransformationMatrix& zoom(double zoomFactor);
+
   bool isInvertible() const;
 
   // This method returns the identity matrix if it is not invertible.
   // Use isInvertible() before calling this if you need to know.
   TransformationMatrix inverse() const;
 
   // decompose the matrix into its component parts
   typedef struct {
     double scaleX, scaleY, scaleZ;
     double skewXY, skewXZ, skewYZ;
@@ skipping 129 matching lines @@
   Matrix4 m_matrix;
 };
 
 // Redeclared here to avoid ODR issues.
 // See platform/testing/TransformPrinters.h.
 void PrintTo(const TransformationMatrix&, std::ostream*);
 
 }  // namespace blink
 
 #endif  // TransformationMatrix_h