iOS – 如何使用openGL绘制YUV图像
目前，我正在尝试使用openGL绘制图像（图像经常更新，因此必须重新绘制）。 以前，我将我的图像从YUV转换为RGB，然后使用这个新图像用openGL绘制。 一切正常，但转换过程并不是特别快。
我现在正在尝试更改代码，以便在openGL着色器中处理转换。 环顾四周之后，我发现了一些代码片段（特别是着色器和我的renderImage函数的大部分），这些代码片段帮助我获得了基线，但我似乎无法真正得到正确绘制的图像 – 所有我曾经看到的是黑色图像。
我很可能错过了一些极其简单和重要的东西 – 我对openGL的体验相当有限。 如果有人可以看看，看看他们是否认识到任何错误，请告诉我。
我应该指出，我正在尝试支持iOS 4.x，因此CVOpenGLESTextureCacheCreateTextureFromImage应该无法使用（即使我愿意，我也不会非常乐意如何设置使用它）。
任何帮助，将不胜感激。 代码如下 –
我的顶点着色器：
attribute vec4 position; attribute vec4 inputTextureCoordinate; varying vec2 textureCoordinate; void main() { gl_Position = position; textureCoordinate = inputTextureCoordinate.xy; } 片段着色器：
#ifdef GL_ES precision mediump float; #endif varying vec2 textureCoordinate; uniform sampler2D videoFrame; uniform sampler2D videoFrameUV; const mat3 yuv2rgb = mat3( 1, 0, 1.2802, 1, -0.214821, -0.380589, 1, 2.127982, 0 ); void main() { vec3 yuv = vec3( 1.1643 * (texture2D(videoFrame, textureCoordinate).r - 0.0625), texture2D(videoFrameUV, textureCoordinate).r - 0.5, texture2D(videoFrameUV, textureCoordinate).a - 0.5 ); vec3 rgb = yuv * yuv2rgb; gl_FragColor = vec4(rgb, 1.0); }
renderImage函数：
-(void)renderImage:(ImageBuffer *)image { if (image) { int bufferHeight = image->GetHeight(); int bufferWidth = image->GetWidth(); if(!imageTexture){ // Dealing with the Y portion of the YCbCr glActiveTexture(GL_TEXTURE0); glGenTextures(1, &imageTexture); //Bind Y texture glBindTexture(GL_TEXTURE_2D, imageTexture); glUniform1i(uniforms[UNIFORM_VIDEOFRAME], 0); // For fitting glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR); glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR); // This is necessary for non-power-of-two textures glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE); glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE); glTexImage2D(GL_TEXTURE_2D, 0, GL_LUMINANCE, bufferWidth, bufferHeight, 0, GL_LUMINANCE, GL_UNSIGNED_BYTE, image->GetPlanePointer(0)); // Dealing with the CbCr potion of the YCbCr glActiveTexture(GL_TEXTURE1); glGenTextures(1, &imageTextureUV); //Bind CbCr texture glBindTexture(GL_TEXTURE_2D, imageTextureUV); glUniform1i(uniforms[UNIFORM_VIDEOFRAMEUV], 1); // For fitting glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR); glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR); // This is necessary for non-power-of-two textures glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE); glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE); glTexImage2D(GL_TEXTURE_2D, 0, GL_LUMINANCE_ALPHA, bufferWidth/2, bufferHeight/2, 0, GL_LUMINANCE_ALPHA, GL_UNSIGNED_BYTE, image->GetPlanePointer(1)); } [self drawFrame]; } }
最后，drawFrame函数：
- (void)drawFrame { [self setFramebuffer]; // Replace the implementation of this method to do your own custom drawing. static const GLfloat squareVertices[] = { -1.0f, -1.0f, 1.0f, -1.0f, -1.0f, 1.0f, 1.0f, 1.0f }; static const GLfloat textureVertices[] = { // 1.0f, 1.0f, // 1.0f, 0.0f, // 0.0f, 1.0f, // 0.0f, 0.0f, 0.0f, 1.0f, 1.0f, 1.0f, 0.0f, 0.0f, 1.0f, 0.0f // 0.0f, 0.8f, // 1.0f, 0.8f, // 0.0f, 0.2f, // 1.0f, 0.2f }; static float transY = 0.0f; if ([context API] == kEAGLRenderingAPIOpenGLES2) { // Use shader program. glUseProgram(program); glActiveTexture(GL_TEXTURE0); glBindTexture(GL_TEXTURE_2D, imageTexture); // Update attribute values. glVertexAttribPointer(ATTRIB_VERTEX, 2, GL_FLOAT, 0, 0, squareVertices); glEnableVertexAttribArray(ATTRIB_VERTEX); glVertexAttribPointer(ATTRIB_TEXTUREPOSITON, 2, GL_FLOAT, 0, 0, textureVertices); glEnableVertexAttribArray(ATTRIB_TEXTUREPOSITON); glActiveTexture(GL_TEXTURE1); glBindTexture(GL_TEXTURE_2D, imageTextureUV); // Update attribute values. glVertexAttribPointer(ATTRIB_VERTEX, 2, GL_FLOAT, 0, 0, squareVertices); glEnableVertexAttribArray(ATTRIB_VERTEX); glVertexAttribPointer(ATTRIB_TEXTUREPOSITON, 2, GL_FLOAT, 0, 0, textureVertices); glEnableVertexAttribArray(ATTRIB_TEXTUREPOSITON); // Validate program before drawing. This is a good check, but only really necessary in a debug build. // DEBUG macro must be defined in your debug configurations if that's not already the case. #if defined(DEBUG) if (![self validateProgram:program]) { NSLog(@"Failed to validate program: %d", program); return; } #endif } else { glMatrixMode(GL_PROJECTION); glLoadIdentity(); glMatrixMode(GL_MODELVIEW); glLoadIdentity(); glTranslatef(0.0f, (GLfloat)(sinf(transY)/2.0f), 0.0f); transY += 0.075f; glVertexPointer(2, GL_FLOAT, 0, squareVertices); glEnableClientState(GL_VERTEX_ARRAY); } glDrawArrays(GL_TRIANGLE_STRIP, 0, 4); [self presentFramebuffer]; }
以下是我的项目“iOS电影播放器”中的一些代码片段。
片段着色器
varying highp vec2 v_texcoord; uniform sampler2D s_texture_y; uniform sampler2D s_texture_u; uniform sampler2D s_texture_v; void main() { highp float y = texture2D(s_texture_y, v_texcoord).r; highp float u = texture2D(s_texture_u, v_texcoord).r - 0.5; highp float v = texture2D(s_texture_v, v_texcoord).r - 0.5; highp float r = y + 1.402 * v; highp float g = y - 0.344 * u - 0.714 * v; highp float b = y + 1.772 * u; gl_FragColor = vec4(r,g,b,1.0); }
2.从YUV420p帧创建纹理
glPixelStorei(GL_UNPACK_ALIGNMENT, 1); glGenTextures(3, _textures); const UInt8 *pixels[3] = { yuvFrame.luma.bytes, yuvFrame.chromaB.bytes, yuvFrame.chromaR.bytes }; const NSUInteger widths[3] = { frameWidth, frameWidth / 2, frameWidth / 2 }; const NSUInteger heights[3] = { frameHeight, frameHeight / 2, frameHeight / 2 }; for (int i = 0; i < 3; ++i) { glBindTexture(GL_TEXTURE_2D, _textures[i]); glTexImage2D(GL_TEXTURE_2D, 0, GL_LUMINANCE, widths[i],heights[i],0,GL_LUMINANCE,GL_UNSIGNED_BYTE,pixels[i]); glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR); glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR); glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE); glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE); }
3.初始化顶点和纹理坐标
static const GLfloat texCoords[] = { 0.0f, 1.0f, 1.0f, 1.0f, 0.0f, 0.0f, 1.0f, 0.0f }; static const GLfloat vertices[]= {-1.0f, -1.0f, 1.0f, -1.0f, -1.0f, 1.0f, 1.0f, 1.0f };
4.渲染帧
[EAGLContext setCurrentContext:_context]; glBindFramebuffer(GL_FRAMEBUFFER, _framebuffer); glViewport(0, 0, _backingWidth, _backingHeight); glClearColor(0.0f, 0.0f, 0.0f, 1.0f); glClear(GL_COLOR_BUFFER_BIT); glUseProgram(_program); for (int i = 0; i < 3; ++i) { glActiveTexture(GL_TEXTURE0 + i); glBindTexture(GL_TEXTURE_2D, _textures[i]); glUniform1i(_uniformSamplers[i], i); } glVertexAttribPointer(ATTRIBUTE_VERTEX, 2, GL_FLOAT, 0, 0, vertices); glEnableVertexAttribArray(ATTRIBUTE_VERTEX); glVertexAttribPointer(ATTRIBUTE_TEXCOORD, 2, GL_FLOAT, 0, 0, texCoords); glEnableVertexAttribArray(ATTRIBUTE_TEXCOORD); glBindRenderbuffer(GL_RENDERBUFFER, _renderbuffer); [_context presentRenderbuffer:GL_RENDERBUFFER];
github上项目的链接 。