将CIFilter应用于OpenGL渲染

我试图在我的全屏渲染输出上应用CoreImage过滤器，但看起来像缺少一些东西，因为我将黑屏作为输出。

首先，我将整个场景绘制成纹理。 然后我创建了CoreImage，然后我最终绘制并呈现该纹理。 但我得到的只是黑屏。 我遵循Apple绘制纹理和将CoreImage与OpenGLES集成的指导原则：WWDC2012 511和https://developer.apple.com/library/ios/documentation/3ddrawing/conceptual/opengles_programmingguide/WorkingwithEAGLContexts/WorkingwithEAGLContexts.html

这里是相关的代码：

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_COLOR_ATTACHMENT0, GL_TEXTURE_2D, _drawTexture, 0);

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

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

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

  return YES;
}

分配内存大小随时更改（初始化和方向更改）：

- (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, 0, GL_RGBA, _backingWidth, _backingHeight, 0, GL_RGBA, GL_UNSIGNED_BYTE, NULL);

  glBindRenderbuffer(GL_RENDERBUFFER, _depthRenderbuffer);
  glRenderbufferStorage(GL_RENDERBUFFER, GL_DEPTH_COMPONENT16, _backingWidth, _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, 0, _backingWidth, _backingHeight) fromRect:CGRectMake(0, 0, _backingWidth, _backingHeight)];

  // Present
  [_context presentRenderbuffer:GL_RENDERBUFFER];
}

请注意，绘制场景后，_drawTexture包含渲染的场景。 我使用Xcode调试工具（Capture OpenGL ES框架）检查了这一点。

编辑：如果我尝试创建CIImage出一些其他纹理然后_drawTexture，它显示正确。 我怀疑是_drawTexture可能没有准备好，或者在CIContext尝试通过CIImage呈现它时被锁定。

编辑2：我也尝试用视口清除替换所有的绘图代码：

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

结果仍然是黑色的。 它表明问题可能与绘制纹理或帧缓冲区有关。

---

我终于发现了什么问题。 iOS上2种纹理的非功率必须具有线性滤波和钳位边缘封装：

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);

我的纹理与屏幕大小相同，但我没有设置这四个参数。

对于后代：上面的代码是OpenGL ES和CoreImage互连的完美示例。 只要确保你正确初始化你的纹理！

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