[Chromoting] Implement GlRenderer

remoting/client/gl_math.h

 // Copyright 2016 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_OPENGL_GL_MATH_H_
 #define REMOTING_CLIENT_OPENGL_GL_MATH_H_
 
 #include <array>
 #include <string>
 
 #include "base/macros.h"
 
 namespace remoting {
 
 // See GlCanvas::SetNormalizedTransformation for definition of the
 // transformation matrix.
 //
-// Converts a pixel based transformation matrix to a texture coordinates based
-// transformation matrix.
-// 3 by 3 transformation matrix, [ m0, m1, m2, m3, m4, m5, m6, m7, m8 ].
+// Converts a pixel based transformation matrix to a **transposed** texture
+// coordinates based transformation matrix.
+// 3 by 3 transformation matrix, [ m0, 0, m2, 0, m4, m5, 0, 0, m8 ].
 //
-// | m0, m1, m2, |   | x |
-// | m3, m4, m5, | * | y |
-// | m6, m7, m8  |   | 1 |
+// | m0,  0, m2, |   | x |
+// |  0, m4, m5, | * | y |
+// |  0,  0, m8  |   | 1 |
+//
+// m1, m3, m6, m7 all must be zero.
 void NormalizeTransformationMatrix(int view_width,
                                    int view_height,
                                    int canvas_width,
                                    int canvas_height,
                                    std::array<float, 9>* matrix);
 
 // Given left, top, width, height of a rectangle, fills |positions| with
 // coordinates of four vertices of the rectangle.
 // positions: [ x_upperleft, y_upperleft, x_lowerleft, y_lowerleft,
 //              x_upperright, y_upperright, x_lowerright, y_lowerright ]
 void FillRectangleVertexPositions(float left,
                                   float top,
                                   float width,
                                   float height,
                                   std::array<float, 8>* positions);
 
 // Returns the string representation of the matrix for debugging.
 //
 // For example:
 // [
 // 1, 0, 0,
 // 0, 1, 0,
 // 0, 0, 1,
 // ]
 std::string MatrixToString(const float* mat, int num_rows, int num_cols);
 
 }  // namespace remoting
 
 #endif  // REMOTING_CLIENT_OPENGL_GL_MATH_H_