iOS: Add support for rendering native CVPixelBuffers directly

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

Index: webrtc/sdk/objc/Framework/Classes/RTCOpenGLVideoRenderer.mm
diff --git a/webrtc/sdk/objc/Framework/Classes/RTCOpenGLVideoRenderer.mm b/webrtc/sdk/objc/Framework/Classes/RTCOpenGLVideoRenderer.mm
index 7d7b416b888843e4028d5068de1362c57fc5f383..5c082f0fb8bc0f1871d91cf6305896eaba022d0c 100644
--- a/webrtc/sdk/objc/Framework/Classes/RTCOpenGLVideoRenderer.mm
+++ b/webrtc/sdk/objc/Framework/Classes/RTCOpenGLVideoRenderer.mm
@@ -11,15 +11,19 @@
 #import "RTCOpenGLVideoRenderer.h"
 
 #if TARGET_OS_IPHONE
+#import <CoreVideo/CVOpenGLESTextureCache.h>
 #import <OpenGLES/ES3/gl.h>
 #else
 #import <OpenGL/gl3.h>
 #endif
-#include <string.h>
 #include <memory>
+#include <string.h>
+#include <vector>
 
 #import "WebRTC/RTCVideoFrame.h"
 
+#include "webrtc/base/checks.h"
+#include "webrtc/base/logging.h"
 
 // TODO(tkchin): check and log openGL errors. Methods here return BOOLs in
 // anticipation of that happening in the future.
@@ -33,6 +37,8 @@
 #define FRAGMENT_SHADER_OUT
 #define FRAGMENT_SHADER_COLOR "gl_FragColor"
 #define FRAGMENT_SHADER_TEXTURE "texture2D"
+
+typedef EAGLContext GlContextType;
 #else
 #define RTC_PIXEL_FORMAT GL_RED
 #define SHADER_VERSION "#version 150\n"
@@ -42,8 +48,14 @@
 #define FRAGMENT_SHADER_OUT "out vec4 fragColor;\n"
 #define FRAGMENT_SHADER_COLOR "fragColor"
 #define FRAGMENT_SHADER_TEXTURE "texture"
+
+typedef NSOpenGLContext GlContextType;
 #endif
 
+@protocol Shader

[tkchin_webrtc, 2016/08/02 00:17:18]

nit: everything in ObjC must be prefixed withthe  project prefix. The reason for
this is because there are no namespaces.
so maybe @protocol RTCOpenGLShader or RTCShader

+- (BOOL)drawFrame:(RTCVideoFrame*)frame;

[tkchin_webrtc, 2016/08/02 00:17:18]

nit: (RTCVideoFrame *)

+@end
+
 // Vertex shader doesn't do anything except pass coordinates through.
 static const char kVertexShaderSource[] =
   SHADER_VERSION
@@ -57,7 +69,7 @@ static const char kVertexShaderSource[] =
 
 // Fragment shader converts YUV values from input textures into a final RGB
 // pixel. The conversion formula is from http://www.fourcc.org/fccyvrgb.php.
-static const char kFragmentShaderSource[] =
+static const char kI420FragmentShaderSource[] =
   SHADER_VERSION
   "precision highp float;"
   FRAGMENT_SHADER_IN " vec2 v_texcoord;\n"
@@ -90,6 +102,15 @@ GLuint CreateShader(GLenum type, const GLchar *source) {
   GLint compileStatus = GL_FALSE;
   glGetShaderiv(shader, GL_COMPILE_STATUS, &compileStatus);
   if (compileStatus == GL_FALSE) {
+    GLint logLength = 0;
+    // The null termination character is included in the returned log length.
+    glGetShaderiv(shader, GL_INFO_LOG_LENGTH, &logLength);
+    if (logLength > 0) {
+      std::unique_ptr<char[]> compileLog(new char[logLength]);
+      // The returned string is null terminated.
+      glGetShaderInfoLog(shader, logLength, NULL, compileLog.get());
+      LOG(LS_ERROR) << "Shader compile error: " << compileLog.get();
+    }
     glDeleteShader(shader);
     shader = 0;
   }
@@ -118,6 +139,25 @@ GLuint CreateProgram(GLuint vertexShader, GLuint fragmentShader) {
   return program;
 }
 
+// Creates and links a shader program with the given fragment shader source and
+// a plain vertex shader. Returns the program handle or 0 on error.
+GLuint CreateProgramFromFragmentSource(const char fragmentShaderSource[]) {
+  GLuint vertexShader = CreateShader(GL_VERTEX_SHADER, kVertexShaderSource);
+  RTC_CHECK(vertexShader) << "failed to create vertex shader";
+  GLuint fragmentShader =
+      CreateShader(GL_FRAGMENT_SHADER, fragmentShaderSource);
+  RTC_CHECK(fragmentShader) << "failed to create fragment shader";
+  GLuint program = CreateProgram(vertexShader, fragmentShader);
+  // Shaders are created only to generate program.
+  if (vertexShader) {
+    glDeleteShader(vertexShader);
+  }
+  if (fragmentShader) {
+    glDeleteShader(fragmentShader);
+  }
+  return program;
+}
+
 // 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
@@ -125,7 +165,7 @@ GLuint CreateProgram(GLuint vertexShader, GLuint fragmentShader) {
 // 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.
-const GLfloat gVertices[] = {
+static const GLfloat gVertices[] = {
   // X, Y, U, V.
   -1, -1, 0, 1,  // Bottom left.
    1, -1, 1, 1,  // Bottom right.
@@ -133,6 +173,46 @@ const GLfloat gVertices[] = {
   -1,  1, 0, 0,  // Top left.
 };
 
+// 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.
+BOOL setupVerticesForProgram(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);
+
+  // 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.
+  glVertexAttribPointer(position, 2, GL_FLOAT, GL_FALSE, 4 * sizeof(GLfloat),
+                        (void*)0);

[tkchin_webrtc, 2016/08/02 00:17:18]

nit: (void *)0
since we're in an ObjC++ file we can also static_cast

+  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)));

[tkchin_webrtc, 2016/08/02 00:17:19]

ditto

+  glEnableVertexAttribArray(texcoord);
+
+  return YES;
+}
+
 // |kNumTextures| must not exceed 8, which is the limit in OpenGLES2. Two sets
 // of 3 textures are used here, one for each of the Y, U and V planes. Having
 // two sets alleviates CPU blockage in the event that the GPU is asked to render
@@ -140,155 +220,68 @@ const GLfloat gVertices[] = {
 static const GLsizei kNumTextureSets = 2;
 static const GLsizei kNumTextures = 3 * kNumTextureSets;
 
-@implementation RTCOpenGLVideoRenderer {
-#if TARGET_OS_IPHONE
-  EAGLContext *_context;
-#else
-  NSOpenGLContext *_context;
-#endif
-  BOOL _isInitialized;
+// Shader for non-native I420 frames.
+@interface I420Shader : NSObject<Shader>

[tkchin_webrtc, 2016/08/02 00:17:18]

nit: style is NSObject <Shader>
together with prefix we get @interface RTCI420Shader : NSObject <RTCShader>

+- (BOOL)drawFrame:(RTCVideoFrame*)frame;

[tkchin_webrtc, 2016/08/02 00:17:19]

don't need to redeclare methods from protocol

+@end
+
+@implementation I420Shader {

[tkchin_webrtc, 2016/08/02 00:17:17]

Can we place the various shaders in their own files?

e.g. RTCI420Shader, RTCNV12Shader

+  BOOL _hasUnpackRowLength;
   GLint _currentTextureSet;
   // Handles for OpenGL constructs.
   GLuint _textures[kNumTextures];
-  GLuint _program;
-#if !TARGET_OS_IPHONE
+  GLuint _i420Program;
   GLuint _vertexArray;
-#endif
   GLuint _vertexBuffer;
-  GLint _position;
-  GLint _texcoord;
   GLint _ySampler;
   GLint _uSampler;
   GLint _vSampler;
   // Used to create a non-padded plane for GPU upload when we receive padded
   // frames.
-  std::unique_ptr<uint8_t[]> _planeBuffer;
-}
-
-@synthesize lastDrawnFrame = _lastDrawnFrame;
-
-+ (void)initialize {
-  // Disable dithering for performance.
-  glDisable(GL_DITHER);
+  std::vector<uint8_t> _planeBuffer;
 }
 
+- (instancetype)initWithContext:(GlContextType *)context {
+  if (self = [super init]) {
 #if TARGET_OS_IPHONE
-- (instancetype)initWithContext:(EAGLContext *)context {
+    _hasUnpackRowLength = (context.API == kEAGLRenderingAPIOpenGLES3);
 #else
-- (instancetype)initWithContext:(NSOpenGLContext *)context {
+    _hasUnpackRowLength = YES;
 #endif
-  NSAssert(context != nil, @"context cannot be nil");
-  if (self = [super init]) {
-    _context = context;
-  }
-  return self;
-}
-
-- (BOOL)drawFrame:(RTCVideoFrame *)frame {
-  if (!_isInitialized) {
-    return NO;
-  }
-  if (_lastDrawnFrame == frame) {
-    return NO;
-  }
-  [self ensureGLContext];
-  glClear(GL_COLOR_BUFFER_BIT);
-  if (frame) {
-    if (![self updateTextureSizesForFrame:frame] ||
-        ![self updateTextureDataForFrame:frame]) {
-      return NO;
+    glPixelStorei(GL_UNPACK_ALIGNMENT, 1);
+    if (![self setupI420Program] || ![self setupTextures] ||
+        !setupVerticesForProgram(_i420Program, &_vertexBuffer, &_vertexArray)) {
+      self = nil;
     }
-#if !TARGET_OS_IPHONE
-    glBindVertexArray(_vertexArray);
-#endif
-    glBindBuffer(GL_ARRAY_BUFFER, _vertexBuffer);
-    glDrawArrays(GL_TRIANGLE_FAN, 0, 4);
   }
-#if !TARGET_OS_IPHONE
-  [_context flushBuffer];
-#endif
-  _lastDrawnFrame = frame;
-  return YES;
+  return self;
 }
 
-- (void)setupGL {
-  if (_isInitialized) {
-    return;
+- (void)dealloc {
+  if (_i420Program != 0) {
+    glDeleteProgram(_i420Program);
   }
-  [self ensureGLContext];
-  if (![self setupProgram]) {
-    return;
-  }
-  if (![self setupTextures]) {
-    return;
-  }
-  if (![self setupVertices]) {
-    return;
+  if (_textures[0] != 0) {
+    glDeleteTextures(kNumTextures, _textures);
   }
-  glUseProgram(_program);
-  glPixelStorei(GL_UNPACK_ALIGNMENT, 1);
-  _isInitialized = YES;
-}
-
-- (void)teardownGL {
-  if (!_isInitialized) {
-    return;
+  if (_vertexBuffer != 0) {
+    glDeleteBuffers(1, &_vertexBuffer);
   }
-  [self ensureGLContext];
-  glDeleteProgram(_program);
-  _program = 0;
-  glDeleteTextures(kNumTextures, _textures);
-  glDeleteBuffers(1, &_vertexBuffer);
-  _vertexBuffer = 0;
-#if !TARGET_OS_IPHONE
-  glDeleteVertexArrays(1, &_vertexArray);
-#endif
-  _isInitialized = NO;
-}
-
-#pragma mark - Private
-
-- (void)ensureGLContext {
-  NSAssert(_context, @"context shouldn't be nil");
-#if TARGET_OS_IPHONE
-  if ([EAGLContext currentContext] != _context) {
-    [EAGLContext setCurrentContext:_context];
-  }
-#else
-  if ([NSOpenGLContext currentContext] != _context) {
-    [_context makeCurrentContext];
+  if (_vertexArray != 0) {
+    glDeleteVertexArrays(1, &_vertexArray);
   }
-#endif
 }
 
-- (BOOL)setupProgram {
-  NSAssert(!_program, @"program already set up");
-  GLuint vertexShader = CreateShader(GL_VERTEX_SHADER, kVertexShaderSource);
-  NSAssert(vertexShader, @"failed to create vertex shader");
-  GLuint fragmentShader =
-      CreateShader(GL_FRAGMENT_SHADER, kFragmentShaderSource);
-  NSAssert(fragmentShader, @"failed to create fragment shader");
-  _program = CreateProgram(vertexShader, fragmentShader);
-  // Shaders are created only to generate program.
-  if (vertexShader) {
-    glDeleteShader(vertexShader);
-  }
-  if (fragmentShader) {
-    glDeleteShader(fragmentShader);
-  }
-  if (!_program) {
-    return NO;
-  }
-  _position = glGetAttribLocation(_program, "position");
-  _texcoord = glGetAttribLocation(_program, "texcoord");
-  _ySampler = glGetUniformLocation(_program, "s_textureY");
-  _uSampler = glGetUniformLocation(_program, "s_textureU");
-  _vSampler = glGetUniformLocation(_program, "s_textureV");
-  if (_position < 0 || _texcoord < 0 || _ySampler < 0 || _uSampler < 0 ||
-      _vSampler < 0) {
+- (BOOL)setupI420Program {
+  _i420Program = CreateProgramFromFragmentSource(kI420FragmentShaderSource);
+  if (!_i420Program) {
     return NO;
   }
-  return YES;
+  _ySampler = glGetUniformLocation(_i420Program, "s_textureY");
+  _uSampler = glGetUniformLocation(_i420Program, "s_textureU");
+  _vSampler = glGetUniformLocation(_i420Program, "s_textureV");
+
+  return (_ySampler >= 0 && _uSampler >= 0 && _vSampler >= 0);

[tkchin_webrtc, 2016/08/02 00:17:19]

these ivars are init-ed to zero by default after init, does getUniformLocation
return -1 on error?

 }
 
 - (BOOL)setupTextures {
@@ -305,56 +298,17 @@ static const GLsizei kNumTextures = 3 * kNumTextureSets;
   return YES;
 }
 
-- (BOOL)updateTextureSizesForFrame:(RTCVideoFrame *)frame {
-  if (frame.height == _lastDrawnFrame.height &&
-      frame.width == _lastDrawnFrame.width &&
-      frame.chromaWidth == _lastDrawnFrame.chromaWidth &&
-      frame.chromaHeight == _lastDrawnFrame.chromaHeight) {
-    return YES;
-  }
-  GLsizei lumaWidth = static_cast<GLsizei>(frame.width);
-  GLsizei lumaHeight = static_cast<GLsizei>(frame.height);
-  GLsizei chromaWidth = static_cast<GLsizei>(frame.chromaWidth);
-  GLsizei chromaHeight = static_cast<GLsizei>(frame.chromaHeight);
-  for (GLint i = 0; i < kNumTextureSets; i++) {
-    glActiveTexture(GL_TEXTURE0 + i * 3);
-    glTexImage2D(GL_TEXTURE_2D,
-                 0,
-                 RTC_PIXEL_FORMAT,
-                 lumaWidth,
-                 lumaHeight,
-                 0,
-                 RTC_PIXEL_FORMAT,
-                 GL_UNSIGNED_BYTE,
-                 0);
-    glActiveTexture(GL_TEXTURE0 + i * 3 + 1);
-    glTexImage2D(GL_TEXTURE_2D,
-                 0,
-                 RTC_PIXEL_FORMAT,
-                 chromaWidth,
-                 chromaHeight,
-                 0,
-                 RTC_PIXEL_FORMAT,
-                 GL_UNSIGNED_BYTE,
-                 0);
-    glActiveTexture(GL_TEXTURE0 + i * 3 + 2);
-    glTexImage2D(GL_TEXTURE_2D,
-                 0,
-                 RTC_PIXEL_FORMAT,
-                 chromaWidth,
-                 chromaHeight,
-                 0,
-                 RTC_PIXEL_FORMAT,
-                 GL_UNSIGNED_BYTE,
-                 0);
-  }
-  if ((NSUInteger)frame.yPitch != frame.width ||
-      (NSUInteger)frame.uPitch != frame.chromaWidth ||
-      (NSUInteger)frame.vPitch != frame.chromaWidth) {
-    _planeBuffer.reset(new uint8_t[frame.width * frame.height]);
-  } else {
-    _planeBuffer.reset();
+- (BOOL)drawFrame:(RTCVideoFrame*)frame {
+  glUseProgram(_i420Program);
+  if (![self updateTextureDataForFrame:frame]) {
+    return NO;
   }
+#if !TARGET_OS_IPHONE
+  glBindVertexArray(_vertexArray);
+#endif
+  glBindBuffer(GL_ARRAY_BUFFER, _vertexBuffer);
+  glDrawArrays(GL_TRIANGLE_FAN, 0, 4);
+
   return YES;
 }
 
@@ -365,17 +319,14 @@ static const GLsizei kNumTextures = 3 * kNumTextureSets;
              height:(size_t)height
              stride:(int32_t)stride {
   glActiveTexture(static_cast<GLenum>(GL_TEXTURE0 + offset));
+  glBindTexture(GL_TEXTURE_2D, _textures[offset]);
+
   // When setting texture sampler uniforms, the texture index is used not
   // the texture handle.
   glUniform1i(sampler, offset);
-#if TARGET_OS_IPHONE
-  BOOL hasUnpackRowLength = _context.API == kEAGLRenderingAPIOpenGLES3;
-#else
-  BOOL hasUnpackRowLength = YES;
-#endif
   const uint8_t *uploadPlane = plane;
   if ((size_t)stride != width) {
-   if (hasUnpackRowLength) {
+   if (_hasUnpackRowLength) {
       // GLES3 allows us to specify stride.
       glPixelStorei(GL_UNPACK_ROW_LENGTH, stride);
       glTexImage2D(GL_TEXTURE_2D,
@@ -392,7 +343,7 @@ static const GLsizei kNumTextures = 3 * kNumTextureSets;
     } else {
       // Make an unpadded copy and upload that instead. Quick profiling showed
       // that this is faster than uploading row by row using glTexSubImage2D.
-      uint8_t *unpaddedPlane = _planeBuffer.get();
+      uint8_t *unpaddedPlane = _planeBuffer.data();
       for (size_t y = 0; y < height; ++y) {
         memcpy(unpaddedPlane + y * width, plane + y * stride, width);
       }
@@ -414,6 +365,12 @@ static const GLsizei kNumTextures = 3 * kNumTextureSets;
   GLint textureOffset = _currentTextureSet * 3;
   NSAssert(textureOffset + 3 <= kNumTextures, @"invalid offset");
 
+  if (frame.yPitch != static_cast<int32_t>(frame.width) ||
+      frame.uPitch != static_cast<int32_t>(frame.chromaWidth) ||
+      frame.vPitch != static_cast<int32_t>(frame.chromaWidth)) {
+    _planeBuffer.resize(frame.width * frame.height);
+  }
+
   [self uploadPlane:frame.yPlane
             sampler:_ySampler
              offset:textureOffset
@@ -439,46 +396,246 @@ static const GLsizei kNumTextures = 3 * kNumTextureSets;
   return YES;
 }
 
-- (BOOL)setupVertices {
-#if !TARGET_OS_IPHONE
-  NSAssert(!_vertexArray, @"vertex array already set up");
-  glGenVertexArrays(1, &_vertexArray);
-  if (!_vertexArray) {
+@end
+
+// Native CVPixelBufferRef rendering is only supported on iPhone because it
+// depends on CVOpenGLESTextureCacheCreate.
+#if TARGET_OS_IPHONE
+static const char kNV12FragmentShaderSource[] =
+  SHADER_VERSION
+  "precision mediump float;"
+  FRAGMENT_SHADER_IN " vec2 v_texcoord;\n"
+  "uniform lowp sampler2D s_textureY;\n"
+  "uniform lowp sampler2D s_textureUV;\n"
+  FRAGMENT_SHADER_OUT
+  "void main() {\n"
+  "    mediump float y;\n"
+  "    mediump vec2 uv;\n"
+  "    y = " FRAGMENT_SHADER_TEXTURE "(s_textureY, v_texcoord).r;\n"
+  "    uv = " FRAGMENT_SHADER_TEXTURE "(s_textureUV, v_texcoord).ra -\n"
+  "        vec2(0.5, 0.5);\n"
+  "    " FRAGMENT_SHADER_COLOR " = vec4(y + 1.403 * uv.y,\n"
+  "                                     y - 0.344 * uv.x - 0.714 * uv.y,\n"
+  "                                     y + 1.770 * uv.x,\n"
+  "                                     1.0);\n"
+  "  }\n";
+
+// Shader for native NV12 frames.
+@interface NativeNV12Shader : NSObject<Shader>
+- (BOOL)drawFrame:(RTCVideoFrame*)frame;
+@end
+
+@implementation NativeNV12Shader {
+  GLuint _vertexBuffer;
+  GLuint _nv12Program;
+  GLint _ySampler;
+  GLint _uvSampler;
+  CVOpenGLESTextureCacheRef _textureCache;
+}
+
+- (instancetype)initWithContext:(GlContextType *)context {
+  if (self = [super init]) {
+    if (![self setupNV12Program] || ![self setupTextureCacheWithContext:context] ||
+        !setupVerticesForProgram(_nv12Program, &_vertexBuffer, nullptr)) {
+      self = nil;
+    }
+  }
+  return self;
+}
+
+- (void)dealloc {
+  if (_nv12Program != 0) {
+    glDeleteProgram(_nv12Program);
+  }
+  if (_vertexBuffer != 0) {
+    glDeleteBuffers(1, &_vertexBuffer);
+  }
+  if (_textureCache) {
+    CFRelease(_textureCache);

[tkchin_webrtc, 2016/08/02 00:17:18]

nit: assign nullptr after release

+  }
+}
+
+- (BOOL)setupNV12Program {
+  _nv12Program = CreateProgramFromFragmentSource(kNV12FragmentShaderSource);
+  if (!_nv12Program) {
     return NO;
   }
-  glBindVertexArray(_vertexArray);
-#endif
-  NSAssert(!_vertexBuffer, @"vertex buffer already set up");
-  glGenBuffers(1, &_vertexBuffer);
-  if (!_vertexBuffer) {
-#if !TARGET_OS_IPHONE
-    glDeleteVertexArrays(1, &_vertexArray);
-    _vertexArray = 0;
+  _ySampler = glGetUniformLocation(_nv12Program, "s_textureY");
+  _uvSampler = glGetUniformLocation(_nv12Program, "s_textureUV");
+
+  return (_ySampler >= 0 && _uvSampler >= 0);
+}
+
+- (BOOL)setupTextureCacheWithContext:(GlContextType *)context {
+  CVReturn err = CVOpenGLESTextureCacheCreate(
+      kCFAllocatorDefault, NULL,
+#if COREVIDEO_USE_EAGLCONTEXT_CLASS_IN_API
+      context,
+#else
+      (__bridge void*)context,

[tkchin_webrtc, 2016/08/02 00:17:17]

nit: void *)

 #endif
+      NULL, &_textureCache);
+  return !err;

[tkchin_webrtc, 2016/08/02 00:17:17]

err == noErr or CVReturnTrue ? I remember there was some special value for this.

+}
+
+- (BOOL)drawFrame:(RTCVideoFrame*)frame {

[tkchin_webrtc, 2016/08/02 00:17:17]

nit: RTCVideoFrame *)

+  CVPixelBufferRef pixelBuffer = frame.nativeHandle;
+  RTC_CHECK(pixelBuffer);
+  glUseProgram(_nv12Program);
+  const OSType pixelFormat = CVPixelBufferGetPixelFormatType(pixelBuffer);
+  RTC_CHECK(pixelFormat == kCVPixelFormatType_420YpCbCr8BiPlanarFullRange ||
+            pixelFormat == kCVPixelFormatType_420YpCbCr8BiPlanarVideoRange)
+      << "Unsupported native pixel format: " << pixelFormat;
+
+  // Y-plane.
+  const int luma_width = CVPixelBufferGetWidthOfPlane(pixelBuffer, 0);

[tkchin_webrtc, 2016/08/02 00:17:18]

nit: camel case instead of underscore for ObjC functions. lumaWidth, lumaHeight

+  const int luma_height = CVPixelBufferGetHeightOfPlane(pixelBuffer, 0);
+
+  CVOpenGLESTextureRef lumaTexture;

[tkchin_webrtc, 2016/08/02 00:17:18]

nit: init to nullptr

+  glActiveTexture(GL_TEXTURE0);
+  glUniform1i(_ySampler, 0);
+  CVReturn err = CVOpenGLESTextureCacheCreateTextureFromImage(
+      kCFAllocatorDefault, _textureCache, pixelBuffer, NULL, GL_TEXTURE_2D,
+      RTC_PIXEL_FORMAT, luma_width, luma_height, RTC_PIXEL_FORMAT,
+      GL_UNSIGNED_BYTE, 0, &lumaTexture);
+  if (err) {
+    CFRelease(lumaTexture);
+    return NO;
+  }
+
+  RTC_CHECK_EQ(static_cast<GLenum>(GL_TEXTURE_2D),
+               CVOpenGLESTextureGetTarget(lumaTexture));
+  glBindTexture(GL_TEXTURE_2D, CVOpenGLESTextureGetName(lumaTexture));
+  glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
+  glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
+  glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
+  glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
+
+  // UV-plane.
+  const int chroma_width = CVPixelBufferGetWidthOfPlane(pixelBuffer, 1);

[tkchin_webrtc, 2016/08/02 00:17:19]

ditto chromeWidth / chromaHeight

+  const int chroma_height = CVPixelBufferGetHeightOfPlane(pixelBuffer, 1);
+
+  CVOpenGLESTextureRef chromaTexture;
+  glActiveTexture(GL_TEXTURE1);
+  glUniform1i(_uvSampler, 1);
+  err = CVOpenGLESTextureCacheCreateTextureFromImage(
+      kCFAllocatorDefault, _textureCache, pixelBuffer, NULL, GL_TEXTURE_2D,
+      GL_LUMINANCE_ALPHA, chroma_width, chroma_height, GL_LUMINANCE_ALPHA,
+      GL_UNSIGNED_BYTE, 1, &chromaTexture);
+  if (err) {
+    CFRelease(chromaTexture);
+    CFRelease(lumaTexture);
     return NO;
   }
+
+  RTC_CHECK_EQ(static_cast<GLenum>(GL_TEXTURE_2D),
+               CVOpenGLESTextureGetTarget(chromaTexture));
+  glBindTexture(GL_TEXTURE_2D, CVOpenGLESTextureGetName(chromaTexture));
+  glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
+  glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
+  glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
+  glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
+
   glBindBuffer(GL_ARRAY_BUFFER, _vertexBuffer);
-  glBufferData(GL_ARRAY_BUFFER, sizeof(gVertices), gVertices, GL_DYNAMIC_DRAW);
+  glDrawArrays(GL_TRIANGLE_FAN, 0, 4);
 
-  // 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.
-  glVertexAttribPointer(
-      _position, 2, GL_FLOAT, GL_FALSE, 4 * sizeof(GLfloat), (void *)0);
-  glEnableVertexAttribArray(_position);
+  CFRelease(chromaTexture);
+  CFRelease(lumaTexture);
 
-  // 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;
+}
+
+@end
+#endif  // TARGET_OS_IPHONE
+
+@implementation RTCOpenGLVideoRenderer {
+  GlContextType* _context;

[tkchin_webrtc, 2016/08/02 00:17:19]

nit: GLContextType *_context

+  BOOL _isInitialized;
+  NSObject<Shader>* _i420Shader;

[tkchin_webrtc, 2016/08/02 00:17:17]

typically we declare id instead of saying that it has to be an NSObject (though
it is pretty much always an NSObject)
id<RTCShader> _i420Shader
id<RTCShader> _nv12Shader

+  NSObject<Shader>* _nv12Shader;
+}
+
+@synthesize lastDrawnFrame = _lastDrawnFrame;
+
++ (void)initialize {
+  // Disable dithering for performance.
+  glDisable(GL_DITHER);
+}
+
+- (instancetype)initWithContext:(GlContextType *)context {
+  NSAssert(context != nil, @"context cannot be nil");
+  if (self = [super init]) {
+    _context = context;
+  }
+  return self;
+}
+
+- (BOOL)drawFrame:(RTCVideoFrame*)frame {
+  if (!_isInitialized || !frame || frame == _lastDrawnFrame) {
+    return NO;
+  }
+  [self ensureGLContext];
+  glClear(GL_COLOR_BUFFER_BIT);
+  NSObject<Shader>* shader;

[tkchin_webrtc, 2016/08/02 00:17:19]

id<RTCShader> shader = nil;

+#if TARGET_OS_IPHONE
+  if (frame.nativeHandle) {
+    if (!_nv12Shader) {
+      _nv12Shader = [[NativeNV12Shader alloc] initWithContext:_context];
+    }
+    shader = _nv12Shader;
+#else
+  // Rendering native CVPixelBuffer is not supported on OS X.
+  if (false) {
+#endif
+  } else {
+    if (!_i420Shader) {
+      _i420Shader = [[I420Shader alloc] initWithContext:_context];
+    }
+    shader = _i420Shader;
+  }
+  if (!shader || ![shader drawFrame:frame]) {
+    return NO;
+  }
+
+#if !TARGET_OS_IPHONE
+  [_context flushBuffer];
+#endif
+  _lastDrawnFrame = frame;
 
   return YES;
 }
 
+- (void)setupGL {
+  if (_isInitialized) {
+    return;
+  }
+  [self ensureGLContext];
+  _isInitialized = YES;
+}
+
+- (void)teardownGL {
+  if (!_isInitialized) {
+    return;
+  }
+  [self ensureGLContext];
+  _i420Shader = nil;
+  _nv12Shader = nil;
+  _isInitialized = NO;
+}
+
+#pragma mark - Private
+
+- (void)ensureGLContext {
+  NSAssert(_context, @"context shouldn't be nil");
+#if TARGET_OS_IPHONE
+  if ([EAGLContext currentContext] != _context) {
+    [EAGLContext setCurrentContext:_context];
+  }
+#else
+  if ([NSOpenGLContext currentContext] != _context) {
+    [_context makeCurrentContext];
+  }
+#endif
+}
+
 @end