[Remoting Client] DesktopViewport Implementation

remoting/client/simple_matrix.h

+// Copyright 2017 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef REMOTING_CLIENT_SIMPLE_MATRIX_H_
+#define REMOTING_CLIENT_SIMPLE_MATRIX_H_

[joedow, 2017/04/28 21:29:53]

Maybe just call this matrix?  It isn't clear why it is simple and we have no
other versions that are complex (to my knowledge).

Perhaps a ViewMatrix is a better term, it seems like the comments below indicate
that is its intended purpose.

[Yuwei, 2017/04/28 23:53:41]

I called it simple because it only needs 3 parameters to represent a 3x3
matrix..
Done.

+
+#include "remoting/client/viewport_geometry.h"
+
+namespace remoting {
+
+// A 2D non-skew equally scaled transformation matrix.
+// | SCALE, 0,     OFFSET_X, |
+// | 0,     SCALE, OFFSET_Y, |
+// | 0,     0,     1         |
+class SimpleMatrix {

[Yuwei, 2017/04/28 02:10:51]

It's possible to use Skia to do matrix calculations but I think:

1. It will increase the binary size by about 1MB.
2. It seems too heavyweight for our simple matrix calculations. (and we
technically only care about three variables)

So I just manually implemented this :)

[joedow, 2017/04/28 21:29:53]

I think saving ~1MB is a good reason since our package is ~7.5MB at the moment.

+ public:
+  SimpleMatrix(float scale, const Vector2D& offset);
+
+  ~SimpleMatrix();
+
+  // Applies the matrix on the point and returns the result.
+  Point MapPoint(const Point& point) const;
+
+  // Applies the matrix on the vector and returns the result. This only scales
+  // the vector and does not apply offset.
+  Vector2D MapVector(const Vector2D& vector) const;
+
+  // Sets the scale factor, with the pivot point at (0, 0). This WON'T affect
+  // the offset.
+  void SetScale(float scale);
+
+  // Returns the scale of this matrix.
+  float GetScale() const;
+
+  // Adjust the matrix M to M' such that:
+  // M * p_a = p_b => M' * p_a = scale * (p_b - pivot) + pivot
+  void PostScale(const Point& pivot, float scale);
+
+  // Applies translation to the matrix.
+  // M * p_a = p_b => M' * p_a = p_b + delta
+  void PostTranslate(const Vector2D& delta);
+
+  // Returns the inverse of this matrix.
+  SimpleMatrix Invert() const;
+
+  // Converts to the 3x3 matrix array.
+  std::array<float, 9> ToMatrixArray() const;
+
+ private:
+  float scale_;
+  Vector2D offset_;
+};
+
+}  // namespace remoting
+
+#endif  // REMOTING_CLIENT_SIMPLE_MATRIX_H_