ios – 将CIFilter应用于OpenGL渲染到纹理

首先我将整个场景画成纹理.然后我从这个纹理创建CoreImage,我终于画出来了.但我所得到的只是黑屏.我正在遵循苹果指南线绘制纹理,并将CoreImage与OpenGLES集成：WWDC2012 511和https://developer.apple.com/library/ios/documentation/3ddrawing/conceptual/opengles_programmingguide/WorkingwithEAGLContexts/WorkingwithEAGLContexts.html

这里是相关代码：

渲染：

@interface Renderer () {
  EAGLContext* _context;
  gluint _defaultFramebuffer,_drawFramebuffer,_depthRenderbuffer,_colorRenderbuffer,_drawTexture;
  GLint _backingWidth,_backingHeight;
  CIImage *_coreImage;
  CIFilter *_coreFilter;
  CIContext *_coreContext;
}

初始化方法：

- (BOOL)initOpenGL
{
  _context = [[EAGLContext alloc] initWithAPI:kEAglrenderingAPIOpenGLES2];
  if (!_context) return NO;

  [EAGLContext setCurrentContext:_context];

  glGenFramebuffers(1,&_defaultFramebuffer);
  glBindFramebuffer(GL_FRAMEBUFFER,_defaultFramebuffer);

  glGenRenderbuffers(1,&_colorRenderbuffer);
  glBindRenderbuffer(GL_RENDERBUFFER,_colorRenderbuffer);
  glFramebufferRenderbuffer(GL_FRAMEBUFFER,GL_COLOR_ATTACHMENT0,GL_RENDERBUFFER,_colorRenderbuffer);

  glGenFramebuffers(1,&_drawFramebuffer);
  glBindFramebuffer(GL_FRAMEBUFFER,_drawFramebuffer);

  glGenTextures(1,&_drawTexture);
  glBindTexture(GL_TEXTURE_2D,_drawTexture);
  glFramebufferTexture2D(GL_FRAMEBUFFER,GL_TEXTURE_2D,_drawTexture,0);

  glGenRenderbuffers(1,&_depthRenderbuffer);
  glBindRenderbuffer(GL_RENDERBUFFER,_depthRenderbuffer);
  glFramebufferRenderbuffer(GL_FRAMEBUFFER,GL_DEPTH_ATTACHMENT,_depthRenderbuffer);

  _coreFilter = [CIFilter filterWithName:@"CIColorInvert"];
  [_coreFilter setDefaults];

  NSDictionary *opts = @{ kCIContextWorkingColorSpace : [NSNull null] };
  _coreContext = [CIContext contextWithEAGLContext:_context options:opts];

  return YES;
}

每当层大小更改(在init和方向更改时)分配内存：

- (void)resizefromLayer:(CAEAGLLayer *)layer
{
  layer.contentsScale = 1;

  glBindFramebuffer(GL_FRAMEBUFFER,_defaultFramebuffer);

  glBindRenderbuffer(GL_RENDERBUFFER,_colorRenderbuffer);
  [_context renderbufferStorage:GL_RENDERBUFFER fromDrawable:layer];

  glGetRenderbufferParameteriv(GL_RENDERBUFFER,GL_RENDERBUFFER_WIDTH,&_backingWidth);
  glGetRenderbufferParameteriv(GL_RENDERBUFFER,GL_RENDERBUFFER_HEIGHT,&_backingHeight);

  // glCheckFramebufferStatus ... SUCCESS

  glBindFramebuffer(GL_FRAMEBUFFER,_drawFramebuffer);

  glBindTexture(GL_TEXTURE_2D,_drawTexture);
  glTexImage2D(GL_TEXTURE_2D,GL_RGBA,_backingWidth,_backingHeight,GL_UNSIGNED_BYTE,NULL);

  glBindRenderbuffer(GL_RENDERBUFFER,_depthRenderbuffer);
  glrenderbufferStorage(GL_RENDERBUFFER,GL_DEPTH_COMPONENT16,_backingHeight);

  // glCheckFramebufferStatus ... SUCCESS
}

绘制方法：

- (void)render:(Scene *)scene
{
  [EAGLContext setCurrentContext:_context];

  glBindFramebuffer(GL_FRAMEBUFFER,_drawFramebuffer);

  // Draw using GLKit,custom shaders,drawArrays,drawElements
  // Now rendered scene is in _drawTexture

  glBindFramebuffer(GL_FRAMEBUFFER,_defaultFramebuffer);
  glBindRenderbuffer(GL_RENDERBUFFER,_colorRenderbuffer);

  // Create CIImage with our render-to-texture texture
  _coreImage = [CIImage imageWithTexture:_drawTexture size:CGSizeMake(_backingWidth,_backingHeight) flipped:NO colorSpace:nil];

  // Ignore filtering for Now; Draw CIImage to current render buffer 
  [_coreContext drawImage:_coreImage inRect:CGRectMake(0,_backingHeight) fromrect:CGRectMake(0,_backingHeight)];

  // Present
  [_context presentRenderbuffer:GL_RENDERBUFFER];
}

注意,绘制场景后,_drawTexture包含渲染场景.我使用Xcode调试工具(Capture OpenGL ES框架)进行检查.

编辑：如果我尝试从一些其他纹理创建CIImage,然后_drawTexture,它正确显示.我的怀疑是,当CIContext尝试通过CIImage呈现时,_drawTexture可能没有准备好或被某种方式锁定.

EDIT2：我也试图用视口清除替换所有绘图代码：

glViewport(0,_backingHeight);
  glClearColor(0,0.8,1);
  glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

结果仍然是黑色的.这表明问题可能是绘制纹理或帧缓冲区的东西.