I used to have a project that used Quartz Composer and OpenGL, but Xcode 13 has deprecated these two components, which caused me to fail to get off-screen images during video production.
The previous code to create the OpenGLContext is as follows：
(id) initOffScreenOpenGLPixelsWide:(unsigned)width pixelsHigh:(unsigned)height
{
//Check parameters - Rendering at sizes smaller than 16x16 will likely produce garbage
if((width < 16) || (height < 16)) {
[self release];
return nil;
}
self = [super init];
if(self != nil) {
NSOpenGLPixelFormatAttribute pixattributes[] = {
NSOpenGLPFADoubleBuffer,
NSOpenGLPFANoRecovery,
NSOpenGLPFAAccelerated,
NSOpenGLPFADepthSize, 24,
(NSOpenGLPixelFormatAttribute) 0
};
_pixelFormat = [[NSOpenGLPixelFormat alloc] initWithAttributes:pixattributes];
//Create the OpenGL context to render with (with color and depth buffers)
_openGLContext = [[NSOpenGLContext alloc] initWithFormat:_pixelFormat shareContext:nil];
if(_openGLContext == nil) {
DDLogInfo(@"Cannot create OpenGL context");
[self release];
return nil;
}
//Create the OpenGL pixel buffer to render into
NSOpenGLPixelBuffer* glPixelBuffer = [[NSOpenGLPixelBuffer alloc] initWithTextureTarget:GL_TEXTURE_RECTANGLE_EXT textureInternalFormat:GL_RGBA textureMaxMipMapLevel:0 pixelsWide:width pixelsHigh:height];
if(glPixelBuffer == nil) {
DDLogInfo(@"Cannot create OpenGL pixel buffer");
[self release];
return nil;
}
[_openGLContext setPixelBuffer:glPixelBuffer cubeMapFace:0 mipMapLevel:0 currentVirtualScreen:[_openGLContext currentVirtualScreen]];
//Destroy the OpenGL pixel buffer
[glPixelBuffer release];
NSMutableDictionary* attributes = [NSMutableDictionary dictionary];
[attributes setObject:[NSNumber numberWithUnsignedInt:k32BGRAPixelFormat] forKey:(NSString*)kCVPixelBufferPixelFormatTypeKey];
[attributes setObject:[NSNumber numberWithUnsignedInt:width] forKey:(NSString*)kCVPixelBufferWidthKey];
[attributes setObject:[NSNumber numberWithUnsignedInt:height] forKey:(NSString*)kCVPixelBufferHeightKey];
//Create buffer pool to hold our frames
OSErr theError = CVPixelBufferPoolCreate(kCFAllocatorDefault, NULL, (CFDictionaryRef)attributes, &_bufferPool);
if(theError != kCVReturnSuccess)
{
DDLogInfo(@"CVPixelBufferPoolCreate() failed with error %i", theError);
[self release];
return nil;
}
}
/*
*A context is current on a per-thread basis. Multiple threads must serialize calls into the same context object.
*/
[self.openGLContext makeCurrentContext];
return self;
}
By creating an NSOpenGLPixelBuffer object, and then setting the pixelbuffer of NSOpenGLContext, but in Xcode13, NSOpenGLPixelBuffer cannot be created successfully. Looking at the help documentation, it is recommended to use GL_EXT_framebuffer_object instead. So I tried the following code:：
//RGBA8 RenderBuffer, 24 bit depth RenderBuffer, 256x256
glGenFramebuffersEXT(1, &fb);
glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, fb);
//Create and attach a color buffer
glGenRenderbuffersEXT(1, &color_rb);
//We must bind color_rb before we call glRenderbufferStorageEXT
glBindRenderbufferEXT(GL_RENDERBUFFER_EXT, color_rb);
//The storage format is RGBA8
glRenderbufferStorageEXT(GL_RENDERBUFFER_EXT, GL_RGBA, width, height);
//Attach color buffer to FBO
glFramebufferRenderbufferEXT(GL_FRAMEBUFFER_EXT, GL_COLOR_ATTACHMENT0_EXT, GL_RENDERBUFFER_EXT, color_rb);
//-------------------------
glGenRenderbuffersEXT(1, &depth_rb);
glBindRenderbufferEXT(GL_RENDERBUFFER_EXT, depth_rb);
glRenderbufferStorageEXT(GL_RENDERBUFFER_EXT, GL_DEPTH_COMPONENT24, width, height);
//-------------------------
//Attach depth buffer to FBO
glFramebufferRenderbufferEXT(GL_FRAMEBUFFER_EXT, GL_DEPTH_ATTACHMENT_EXT, GL_RENDERBUFFER_EXT, depth_rb);
//-------------------------
//Does the GPU support current FBO configuration?
GLenum status;
status = glCheckFramebufferStatusEXT(GL_FRAMEBUFFER_EXT);
switch(status)
{
case GL_FRAMEBUFFER_COMPLETE_EXT:
DDLogInfo(@"gl no problem");
break;
default:
DDLogInfo(@"error");
break;
}
//-------------------------
//and now you can render to the FBO (also called RenderBuffer)
glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, fb);
When running the program we can get the 'gl no problem' log.
However, when reading off-screen image data, although glGetError does not return an error code, I can only read a black image. In previous versions, a QCRenderer rendered image could be successfully obtained.
Reading off-screen images is implemented as follows:
(CVPixelBufferRef) readPixelBuffer
{
// Create pixel buffer from pixel buffer pool
CVPixelBufferRef bufferRef;
OSErr theError = CVPixelBufferPoolCreatePixelBuffer(kCFAllocatorDefault, _bufferPool, &bufferRef);
if(theError) {
DDLogInfo(@"CVPixelBufferPoolCreatePixelBuffer() failed with error %i", theError);
return nil;
}
theError = CVPixelBufferLockBaseAddress(bufferRef, 0);
if(theError) {
DDLogInfo(@"CVPixelBufferLockBaseAddress() failed with error %i", theError);
return nil;
}
void* bufferPtr = CVPixelBufferGetBaseAddress(bufferRef);
size_t width = CVPixelBufferGetWidth(bufferRef);
size_t height = CVPixelBufferGetHeight(bufferRef);
size_t bufferRowBytes = CVPixelBufferGetBytesPerRow(bufferRef);
CGLContextObj cgl_ctx = [_openGLContext CGLContextObj];
CGLLockContext(cgl_ctx);
//Read pixels back from the OpenGL pixel buffer in ARGB 32 bits format - For extra safety, we save / restore the OpenGL states we change
GLint save;
glGetIntegerv(GL_PACK_ROW_LENGTH, &save);
glPixelStorei(GL_PACK_ROW_LENGTH, (int)bufferRowBytes / 4);
glReadPixels(0, 0, (GLsizei)width, (GLsizei)height, GL_BGRA, GL_UNSIGNED_INT_8_8_8_8_REV, bufferPtr);
flipImage(bufferPtr, width, height, bufferRowBytes);
glPixelStorei(GL_PACK_ROW_LENGTH, save);
CGLUnlockContext(cgl_ctx);
GLenum code = glGetError();
if(code)
return nil;
CVPixelBufferUnlockBaseAddress(bufferRef, 0);
return bufferRef;
}
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