iOS render: Handle frame rotation in OpenGL

webrtc/sdk/objc/Framework/Classes/RTCShader.mm

 /*
  *  Copyright 2016 The WebRTC project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 10 matching lines @@
 const char kRTCVertexShaderSource[] =
   SHADER_VERSION
   VERTEX_SHADER_IN " vec2 position;\n"
   VERTEX_SHADER_IN " vec2 texcoord;\n"
   VERTEX_SHADER_OUT " vec2 v_texcoord;\n"
   "void main() {\n"
   "    gl_Position = vec4(position.x, position.y, 0.0, 1.0);\n"
   "    v_texcoord = texcoord;\n"
   "}\n";
 
-// When modelview and projection matrices are identity (default) the world is
-// contained in the square around origin with unit size 2. Drawing to these
-// coordinates is equivalent to drawing to the entire screen. The texture is
-// stretched over that square using texture coordinates (u, v) that range
-// from (0, 0) to (1, 1) inclusive. Texture coordinates are flipped vertically
-// here because the incoming frame has origin in upper left hand corner but
-// OpenGL expects origin in bottom left corner.
-static const GLfloat gVertices[] = {
-  // X, Y, U, V.
-  -1, -1, 0, 1,  // Bottom left.
-   1, -1, 1, 1,  // Bottom right.
-   1,  1, 1, 0,  // Top right.
-  -1,  1, 0, 0,  // Top left.
-};
-
 // Compiles a shader of the given |type| with GLSL source |source| and returns
 // the shader handle or 0 on error.
 GLuint RTCCreateShader(GLenum type, const GLchar *source) {
   GLuint shader = glCreateShader(type);
   if (!shader) {
     return 0;
   }
   glShaderSource(shader, 1, &source, NULL);
   glCompileShader(shader);
   GLint compileStatus = GL_FALSE;
@@ skipping 48 matching lines @@
   // Shaders are created only to generate program.
   if (vertexShader) {
     glDeleteShader(vertexShader);
   }
   if (fragmentShader) {
     glDeleteShader(fragmentShader);
   }
   return program;
 }
 
-// Set vertex shader variables 'position' and 'texcoord' in |program| to the
-// |gVertices| array above. It will use |vertexBuffer| and |vertexArray| to
-// store the vertex data.
+// Set vertex shader variables 'position' and 'texcoord' in |program| to use
+// |vertexBuffer| and |vertexArray| to store the vertex data.
 BOOL RTCSetupVerticesForProgram(GLuint program, GLuint* vertexBuffer, GLuint* vertexArray) {
   GLint position = glGetAttribLocation(program, "position");
   GLint texcoord = glGetAttribLocation(program, "texcoord");
   if (position < 0 || texcoord < 0) {
     return NO;
   }
 #if !TARGET_OS_IPHONE
   glGenVertexArrays(1, vertexArray);
   if (*vertexArray == 0) {
     return NO;
   }
   glBindVertexArray(*vertexArray);
 #endif
   glGenBuffers(1, vertexBuffer);
   if (*vertexBuffer == 0) {
     return NO;
   }
   glBindBuffer(GL_ARRAY_BUFFER, *vertexBuffer);
-  glBufferData(GL_ARRAY_BUFFER, sizeof(gVertices), gVertices, GL_DYNAMIC_DRAW);
+  glBufferData(GL_ARRAY_BUFFER, 4 * 4 * sizeof(GLfloat), NULL, GL_DYNAMIC_DRAW);
 
-  // Read position attribute from |gVertices| with size of 2 and stride of 4
-  // beginning at the start of the array. The last argument indicates offset
-  // of data within |gVertices| as supplied to the vertex buffer.
+  // Read position attribute with size of 2 and stride of 4 beginning at the
+  // start of the array. The last argument indicates offset of data within the
+  // vertex buffer.
   glVertexAttribPointer(position, 2, GL_FLOAT, GL_FALSE, 4 * sizeof(GLfloat),
                         (void *)0);
   glEnableVertexAttribArray(position);
 
   // Read texcoord attribute from |gVertices| with size of 2 and stride of 4
   // beginning at the first texcoord in the array. The last argument indicates
   // offset of data within |gVertices| as supplied to the vertex buffer.
   glVertexAttribPointer(texcoord, 2, GL_FLOAT, GL_FALSE, 4 * sizeof(GLfloat),
                         (void *)(2 * sizeof(GLfloat)));
   glEnableVertexAttribArray(texcoord);
 
   return YES;
 }
+
+// Set vertex data to the currently bound vertex buffer.
+void RTCSetVertexData(int rotation) {
+  // When modelview and projection matrices are identity (default) the world is
+  // contained in the square around origin with unit size 2. Drawing to these
+  // coordinates is equivalent to drawing to the entire screen. The texture is
+  // stretched over that square using texture coordinates (u, v) that range
+  // from (0, 0) to (1, 1) inclusive. Texture coordinates are flipped vertically
+  // here because the incoming frame has origin in upper left hand corner but
+  // OpenGL expects origin in bottom left corner.
+  static const GLfloat UVCoords[4][2] = {
+    {0, 1},  // Lower left.
+    {1, 1},  // Lower right.
+    {1, 0},  // Upper right.
+    {0, 0},  // Upper left.
+  };
+
+  const int offset = rotation / 90;
+  const GLfloat gVertices[] = {
+    // X, Y, U, V.
+    -1, -1, UVCoords[(offset + 0) % 4][0], UVCoords[(offset + 0) % 4][1],
+     1, -1, UVCoords[(offset + 1) % 4][0], UVCoords[(offset + 1) % 4][1],
+     1,  1, UVCoords[(offset + 2) % 4][0], UVCoords[(offset + 2) % 4][1],
+    -1,  1, UVCoords[(offset + 3) % 4][0], UVCoords[(offset + 3) % 4][1],
+  };
+
+  glBufferSubData(GL_ARRAY_BUFFER, 0, sizeof(gVertices), gVertices);
+}