webrtc/api/objc/RTCOpenGLVideoRenderer.mm - src/ - Git at Google

 /*
  *  Copyright 2015 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.
  */

 #import "RTCOpenGLVideoRenderer.h"

 #include <string.h>

 #include "webrtc/base/scoped_ptr.h"

 #if TARGET_OS_IPHONE
 #import <OpenGLES/ES3/gl.h>
 #else
 #import <OpenGL/gl3.h>
 #endif

 #import "RTCVideoFrame.h"

 // TODO(tkchin): check and log openGL errors. Methods here return BOOLs in
 // anticipation of that happening in the future.

 #if TARGET_OS_IPHONE
 #define RTC_PIXEL_FORMAT GL_LUMINANCE
 #define SHADER_VERSION
 #define VERTEX_SHADER_IN "attribute"
 #define VERTEX_SHADER_OUT "varying"
 #define FRAGMENT_SHADER_IN "varying"
 #define FRAGMENT_SHADER_OUT
 #define FRAGMENT_SHADER_COLOR "gl_FragColor"
 #define FRAGMENT_SHADER_TEXTURE "texture2D"
 #else
 #define RTC_PIXEL_FORMAT GL_RED
 #define SHADER_VERSION "#version 150\n"
 #define VERTEX_SHADER_IN "in"
 #define VERTEX_SHADER_OUT "out"
 #define FRAGMENT_SHADER_IN "in"
 #define FRAGMENT_SHADER_OUT "out vec4 fragColor;\n"
 #define FRAGMENT_SHADER_COLOR "fragColor"
 #define FRAGMENT_SHADER_TEXTURE "texture"
 #endif

 // Vertex shader doesn't do anything except pass coordinates through.
 static const char kVertexShaderSource[] =
   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";

 // 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[] =
   SHADER_VERSION
   "precision highp float;"
   FRAGMENT_SHADER_IN " vec2 v_texcoord;\n"
   "uniform lowp sampler2D s_textureY;\n"
   "uniform lowp sampler2D s_textureU;\n"
   "uniform lowp sampler2D s_textureV;\n"
   FRAGMENT_SHADER_OUT
   "void main() {\n"
   "    float y, u, v, r, g, b;\n"
   "    y = " FRAGMENT_SHADER_TEXTURE "(s_textureY, v_texcoord).r;\n"
   "    u = " FRAGMENT_SHADER_TEXTURE "(s_textureU, v_texcoord).r;\n"
   "    v = " FRAGMENT_SHADER_TEXTURE "(s_textureV, v_texcoord).r;\n"
   "    u = u - 0.5;\n"
   "    v = v - 0.5;\n"
   "    r = y + 1.403 * v;\n"
   "    g = y - 0.344 * u - 0.714 * v;\n"
   "    b = y + 1.770 * u;\n"
   "    " FRAGMENT_SHADER_COLOR " = vec4(r, g, b, 1.0);\n"
   "  }\n";

 // Compiles a shader of the given |type| with GLSL source |source| and returns
 // the shader handle or 0 on error.
 GLuint CreateShader(GLenum type, const GLchar *source) {
   GLuint shader = glCreateShader(type);
   if (!shader) {
     return 0;
   }
   glShaderSource(shader, 1, &source, NULL);
   glCompileShader(shader);
   GLint compileStatus = GL_FALSE;
   glGetShaderiv(shader, GL_COMPILE_STATUS, &compileStatus);
   if (compileStatus == GL_FALSE) {
     glDeleteShader(shader);
     shader = 0;
   }
   return shader;
 }

 // Links a shader program with the given vertex and fragment shaders and
 // returns the program handle or 0 on error.
 GLuint CreateProgram(GLuint vertexShader, GLuint fragmentShader) {
   if (vertexShader == 0 || fragmentShader == 0) {
     return 0;
   }
   GLuint program = glCreateProgram();
   if (!program) {
     return 0;
   }
   glAttachShader(program, vertexShader);
   glAttachShader(program, fragmentShader);
   glLinkProgram(program);
   GLint linkStatus = GL_FALSE;
   glGetProgramiv(program, GL_LINK_STATUS, &linkStatus);
   if (linkStatus == GL_FALSE) {
     glDeleteProgram(program);
     program = 0;
   }
   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
 // 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.
 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.
 };

 // |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
 // to a texture that is already in use.
 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;
   NSUInteger _currentTextureSet;
   // Handles for OpenGL constructs.
   GLuint _textures[kNumTextures];
   GLuint _program;
 #if !TARGET_OS_IPHONE
   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.
   rtc::scoped_ptr<uint8_t[]> _planeBuffer;
 }

 @synthesize lastDrawnFrame = _lastDrawnFrame;

 + (void)initialize {
   // Disable dithering for performance.
   glDisable(GL_DITHER);
 }

 #if TARGET_OS_IPHONE
 - (instancetype)initWithContext:(EAGLContext *)context {
 #else
 - (instancetype)initWithContext:(NSOpenGLContext *)context {
 #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;
     }
 #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;
 }

 - (void)setupGL {
   if (_isInitialized) {
     return;
   }
   [self ensureGLContext];
   if (![self setupProgram]) {
     return;
   }
   if (![self setupTextures]) {
     return;
   }
   if (![self setupVertices]) {
     return;
   }
   glUseProgram(_program);
   glPixelStorei(GL_UNPACK_ALIGNMENT, 1);
   _isInitialized = YES;
 }

 - (void)teardownGL {
   if (!_isInitialized) {
     return;
   }
   [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];
   }
 #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) {
     return NO;
   }
   return YES;
 }

 - (BOOL)setupTextures {
   glGenTextures(kNumTextures, _textures);
   // Set parameters for each of the textures we created.
   for (GLsizei i = 0; i < kNumTextures; i++) {
     glActiveTexture(GL_TEXTURE0 + i);
     glBindTexture(GL_TEXTURE_2D, _textures[i]);
     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);
   }
   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 = frame.width;
   GLsizei lumaHeight = frame.height;
   GLsizei chromaWidth = frame.chromaWidth;
   GLsizei chromaHeight = 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();
   }
   return YES;
 }

 - (void)uploadPlane:(const uint8_t *)plane
             sampler:(GLint)sampler
              offset:(NSUInteger)offset
               width:(size_t)width
              height:(size_t)height
              stride:(int32_t)stride {
   glActiveTexture(GL_TEXTURE0 + 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) {
       // GLES3 allows us to specify stride.
       glPixelStorei(GL_UNPACK_ROW_LENGTH, stride);
       glTexImage2D(GL_TEXTURE_2D,
                    0,
                    RTC_PIXEL_FORMAT,
                    width,
                    height,
                    0,
                    RTC_PIXEL_FORMAT,
                    GL_UNSIGNED_BYTE,
                    uploadPlane);
       glPixelStorei(GL_UNPACK_ROW_LENGTH, 0);
       return;
     } 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();
       for (size_t y = 0; y < height; ++y) {
         memcpy(unpaddedPlane + y * width, plane + y * stride, width);
       }
       uploadPlane = unpaddedPlane;
     }
   }
   glTexImage2D(GL_TEXTURE_2D,
                0,
                RTC_PIXEL_FORMAT,
                width,
                height,
                0,
                RTC_PIXEL_FORMAT,
                GL_UNSIGNED_BYTE,
                uploadPlane);
 }

 - (BOOL)updateTextureDataForFrame:(RTCVideoFrame *)frame {
   NSUInteger textureOffset = _currentTextureSet * 3;
   NSAssert(textureOffset + 3 <= kNumTextures, @"invalid offset");

   [self uploadPlane:frame.yPlane
             sampler:_ySampler
              offset:textureOffset
               width:frame.width
              height:frame.height
              stride:frame.yPitch];

   [self uploadPlane:frame.uPlane
             sampler:_uSampler
              offset:textureOffset + 1
               width:frame.chromaWidth
              height:frame.chromaHeight
              stride:frame.uPitch];

   [self uploadPlane:frame.vPlane
             sampler:_vSampler
              offset:textureOffset + 2
               width:frame.chromaWidth
              height:frame.chromaHeight
              stride:frame.vPitch];

   _currentTextureSet = (_currentTextureSet + 1) % kNumTextureSets;
   return YES;
 }

 - (BOOL)setupVertices {
 #if !TARGET_OS_IPHONE
   NSAssert(!_vertexArray, @"vertex array already set up");
   glGenVertexArrays(1, &_vertexArray);
   if (!_vertexArray) {
     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;
 #endif
     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);
   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;
 }

 @end
	/*
	* Copyright 2015 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.
	*/

	#import "RTCOpenGLVideoRenderer.h"

	#include <string.h>

	#include "webrtc/base/scoped_ptr.h"

	#if TARGET_OS_IPHONE
	#import <OpenGLES/ES3/gl.h>
	#else
	#import <OpenGL/gl3.h>
	#endif

	#import "RTCVideoFrame.h"

	// TODO(tkchin): check and log openGL errors. Methods here return BOOLs in
	// anticipation of that happening in the future.

	#if TARGET_OS_IPHONE
	#define RTC_PIXEL_FORMAT GL_LUMINANCE
	#define SHADER_VERSION
	#define VERTEX_SHADER_IN "attribute"
	#define VERTEX_SHADER_OUT "varying"
	#define FRAGMENT_SHADER_IN "varying"
	#define FRAGMENT_SHADER_OUT
	#define FRAGMENT_SHADER_COLOR "gl_FragColor"
	#define FRAGMENT_SHADER_TEXTURE "texture2D"
	#else
	#define RTC_PIXEL_FORMAT GL_RED
	#define SHADER_VERSION "#version 150\n"
	#define VERTEX_SHADER_IN "in"
	#define VERTEX_SHADER_OUT "out"
	#define FRAGMENT_SHADER_IN "in"
	#define FRAGMENT_SHADER_OUT "out vec4 fragColor;\n"
	#define FRAGMENT_SHADER_COLOR "fragColor"
	#define FRAGMENT_SHADER_TEXTURE "texture"
	#endif

	// Vertex shader doesn't do anything except pass coordinates through.
	static const char kVertexShaderSource[] =
	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";

	// 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[] =
	SHADER_VERSION
	"precision highp float;"
	FRAGMENT_SHADER_IN " vec2 v_texcoord;\n"
	"uniform lowp sampler2D s_textureY;\n"
	"uniform lowp sampler2D s_textureU;\n"
	"uniform lowp sampler2D s_textureV;\n"
	FRAGMENT_SHADER_OUT
	"void main() {\n"
	" float y, u, v, r, g, b;\n"
	" y = " FRAGMENT_SHADER_TEXTURE "(s_textureY, v_texcoord).r;\n"
	" u = " FRAGMENT_SHADER_TEXTURE "(s_textureU, v_texcoord).r;\n"
	" v = " FRAGMENT_SHADER_TEXTURE "(s_textureV, v_texcoord).r;\n"
	" u = u - 0.5;\n"
	" v = v - 0.5;\n"
	" r = y + 1.403 * v;\n"
	" g = y - 0.344 * u - 0.714 * v;\n"
	" b = y + 1.770 * u;\n"
	" " FRAGMENT_SHADER_COLOR " = vec4(r, g, b, 1.0);\n"
	" }\n";

	// Compiles a shader of the given \|type\| with GLSL source \|source\| and returns
	// the shader handle or 0 on error.
	GLuint CreateShader(GLenum type, const GLchar *source) {
	GLuint shader = glCreateShader(type);
	if (!shader) {
	return 0;
	}
	glShaderSource(shader, 1, &source, NULL);
	glCompileShader(shader);
	GLint compileStatus = GL_FALSE;
	glGetShaderiv(shader, GL_COMPILE_STATUS, &compileStatus);
	if (compileStatus == GL_FALSE) {
	glDeleteShader(shader);
	shader = 0;
	}
	return shader;
	}

	// Links a shader program with the given vertex and fragment shaders and
	// returns the program handle or 0 on error.
	GLuint CreateProgram(GLuint vertexShader, GLuint fragmentShader) {
	if (vertexShader == 0 \|\| fragmentShader == 0) {
	return 0;
	}
	GLuint program = glCreateProgram();
	if (!program) {
	return 0;
	}
	glAttachShader(program, vertexShader);
	glAttachShader(program, fragmentShader);
	glLinkProgram(program);
	GLint linkStatus = GL_FALSE;
	glGetProgramiv(program, GL_LINK_STATUS, &linkStatus);
	if (linkStatus == GL_FALSE) {
	glDeleteProgram(program);
	program = 0;
	}
	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
	// 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.
	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.
	};

	// \|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
	// to a texture that is already in use.
	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;
	NSUInteger _currentTextureSet;
	// Handles for OpenGL constructs.
	GLuint _textures[kNumTextures];
	GLuint _program;
	#if !TARGET_OS_IPHONE
	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.
	rtc::scoped_ptr<uint8_t[]> _planeBuffer;
	}

	@synthesize lastDrawnFrame = _lastDrawnFrame;

	+ (void)initialize {
	// Disable dithering for performance.
	glDisable(GL_DITHER);
	}

	#if TARGET_OS_IPHONE
	- (instancetype)initWithContext:(EAGLContext *)context {
	#else
	- (instancetype)initWithContext:(NSOpenGLContext *)context {
	#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;
	}
	#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;
	}

	- (void)setupGL {
	if (_isInitialized) {
	return;
	}
	[self ensureGLContext];
	if (![self setupProgram]) {
	return;
	}
	if (![self setupTextures]) {
	return;
	}
	if (![self setupVertices]) {
	return;
	}
	glUseProgram(_program);
	glPixelStorei(GL_UNPACK_ALIGNMENT, 1);
	_isInitialized = YES;
	}

	- (void)teardownGL {
	if (!_isInitialized) {
	return;
	}
	[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];
	}
	#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) {
	return NO;
	}
	return YES;
	}

	- (BOOL)setupTextures {
	glGenTextures(kNumTextures, _textures);
	// Set parameters for each of the textures we created.
	for (GLsizei i = 0; i < kNumTextures; i++) {
	glActiveTexture(GL_TEXTURE0 + i);
	glBindTexture(GL_TEXTURE_2D, _textures[i]);
	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);
	}
	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 = frame.width;
	GLsizei lumaHeight = frame.height;
	GLsizei chromaWidth = frame.chromaWidth;
	GLsizei chromaHeight = 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();
	}
	return YES;
	}

	- (void)uploadPlane:(const uint8_t *)plane
	sampler:(GLint)sampler
	offset:(NSUInteger)offset
	width:(size_t)width
	height:(size_t)height
	stride:(int32_t)stride {
	glActiveTexture(GL_TEXTURE0 + 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) {
	// GLES3 allows us to specify stride.
	glPixelStorei(GL_UNPACK_ROW_LENGTH, stride);
	glTexImage2D(GL_TEXTURE_2D,
	0,
	RTC_PIXEL_FORMAT,
	width,
	height,
	0,
	RTC_PIXEL_FORMAT,
	GL_UNSIGNED_BYTE,
	uploadPlane);
	glPixelStorei(GL_UNPACK_ROW_LENGTH, 0);
	return;
	} 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();
	for (size_t y = 0; y < height; ++y) {
	memcpy(unpaddedPlane + y * width, plane + y * stride, width);
	}
	uploadPlane = unpaddedPlane;
	}
	}
	glTexImage2D(GL_TEXTURE_2D,
	0,
	RTC_PIXEL_FORMAT,
	width,
	height,
	0,
	RTC_PIXEL_FORMAT,
	GL_UNSIGNED_BYTE,
	uploadPlane);
	}

	- (BOOL)updateTextureDataForFrame:(RTCVideoFrame *)frame {
	NSUInteger textureOffset = _currentTextureSet * 3;
	NSAssert(textureOffset + 3 <= kNumTextures, @"invalid offset");

	[self uploadPlane:frame.yPlane
	sampler:_ySampler
	offset:textureOffset
	width:frame.width
	height:frame.height
	stride:frame.yPitch];

	[self uploadPlane:frame.uPlane
	sampler:_uSampler
	offset:textureOffset + 1
	width:frame.chromaWidth
	height:frame.chromaHeight
	stride:frame.uPitch];

	[self uploadPlane:frame.vPlane
	sampler:_vSampler
	offset:textureOffset + 2
	width:frame.chromaWidth
	height:frame.chromaHeight
	stride:frame.vPitch];

	_currentTextureSet = (_currentTextureSet + 1) % kNumTextureSets;
	return YES;
	}

	- (BOOL)setupVertices {
	#if !TARGET_OS_IPHONE
	NSAssert(!_vertexArray, @"vertex array already set up");
	glGenVertexArrays(1, &_vertexArray);
	if (!_vertexArray) {
	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;
	#endif
	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);
	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;
	}

	@end