OpenGL ES snapshot for openFrameworks, Apple implementation

ofxiPhoneScreenGrab.cpp

void ofxiPhoneScreenGrab(id delegate) {
    
    // Technical Q&A QA1704
    // How do I take a snapshot of my OpenGL ES view and save the result in a UIImage?
    // http://developer.apple.com/library/ios/#qa/qa1704/_index.html

    GLint backingWidth, backingHeight;
    
    // Bind the color renderbuffer used to render the OpenGL ES view
    // If your application only creates a single color renderbuffer which is already bound at this point, 
    // this call is redundant, but it is needed if you're dealing with multiple renderbuffers.
    // Note, replace "_colorRenderbuffer" with the actual name of the renderbuffer object defined in your class.

    //glBindRenderbufferOES(GL_RENDERBUFFER_OES, colorRenderbuffer);
    

    // http://stackoverflow.com/questions/6869577/problem-in-reading-data-using-glreadpixel
    // http://stackoverflow.com/questions/7402504/multisampled-render-to-texture-in-ios
    
    // not working
         
    GLuint sampleFramebuffer, framebuffer;
    
    glGenFramebuffersOES(1, &sampleFramebuffer);
    glGenFramebuffersOES(1, &framebuffer);
    
    glBindFramebufferOES(GL_READ_FRAMEBUFFER_APPLE, sampleFramebuffer); 
    
    glBindFramebufferOES(GL_DRAW_FRAMEBUFFER_APPLE, framebuffer); 

    glResolveMultisampleFramebufferAPPLE();

    NSLog(@"resolve 0x%x", glGetError()); // 0x0506 GL_INVALID_FRAMEBUFFER_OPERATION                    

    glBindFramebufferOES(GL_FRAMEBUFFER_OES, framebuffer);    
    
    GLenum status = glCheckFramebufferStatus(GL_FRAMEBUFFER) ;
    if(status != GL_FRAMEBUFFER_COMPLETE) {
        NSLog(@"failed to make complete framebuffer object %x", status);
    }

    
    // -------------


    // Get the size of the backing CAEAGLLayer
    glGetRenderbufferParameterivOES(GL_RENDERBUFFER_OES, GL_RENDERBUFFER_WIDTH_OES, &backingWidth);
    glGetRenderbufferParameterivOES(GL_RENDERBUFFER_OES, GL_RENDERBUFFER_HEIGHT_OES, &backingHeight);
    
    NSInteger x = 0, y = 0, width = backingWidth, height = backingHeight;
    NSInteger dataLength = width * height * 4;
    GLubyte *data = (GLubyte*)malloc(dataLength * sizeof(GLubyte));
        
    // Read pixel data from the framebuffer
    glPixelStorei(GL_PACK_ALIGNMENT, 4);
    glReadPixels(x, y, width, height, GL_RGBA, GL_UNSIGNED_BYTE, data);
    
    // Create a CGImage with the pixel data
    // If your OpenGL ES content is opaque, use kCGImageAlphaNoneSkipLast to ignore the alpha channel
    // otherwise, use kCGImageAlphaPremultipliedLast
    CGDataProviderRef ref = CGDataProviderCreateWithData(NULL, data, dataLength, NULL);
    CGColorSpaceRef colorspace = CGColorSpaceCreateDeviceRGB();
    CGImageRef iref = CGImageCreate(width, height, 8, 32, width * 4, colorspace, kCGBitmapByteOrder32Big | kCGImageAlphaPremultipliedLast,
                                    ref, NULL, true, kCGRenderingIntentDefault);
    
    // OpenGL ES measures data in PIXELS
    // Create a graphics context with the target size measured in POINTS
    NSInteger widthInPoints, heightInPoints;
    if (NULL != UIGraphicsBeginImageContextWithOptions) {
        // On iOS 4 and later, use UIGraphicsBeginImageContextWithOptions to take the scale into consideration
        // Set the scale parameter to your OpenGL ES view's contentScaleFactor
        // so that you get a high-resolution snapshot when its value is greater than 1.0
        //CGFloat scale = 2.0; //eaglview.contentScaleFactor;
        CGFloat scale = [ofxiPhoneGetAppDelegate() getGLView].contentScaleFactor;
        widthInPoints = width / scale;
        heightInPoints = height / scale;
        UIGraphicsBeginImageContextWithOptions(CGSizeMake(widthInPoints, heightInPoints), NO, scale);
    }
    else {
        // On iOS prior to 4, fall back to use UIGraphicsBeginImageContext
        widthInPoints = width;
        heightInPoints = height;
        UIGraphicsBeginImageContext(CGSizeMake(widthInPoints, heightInPoints));
    }
    
    CGContextRef cgcontext = UIGraphicsGetCurrentContext();
    
    // UIKit coordinate system is upside down to GL/Quartz coordinate system
    // Flip the CGImage by rendering it to the flipped bitmap context
    // The size of the destination area is measured in POINTS
    CGContextSetBlendMode(cgcontext, kCGBlendModeCopy);
    CGContextDrawImage(cgcontext, CGRectMake(0.0, 0.0, widthInPoints, heightInPoints), iref);
    
    // Retrieve the UIImage from the current context
    UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
    
    // rewrap to get PNG file
    NSData* imdata =  UIImagePNGRepresentation ( image ); // get PNG representation
    UIImage* im2 = [UIImage imageWithData:imdata]; // wrap UIImage around PNG representation
    
    SaveDelegate *saveDelegate = [SaveDelegate new];
	saveDelegate.delegate = delegate;
    
    UIImageWriteToSavedPhotosAlbum(im2, saveDelegate, @selector(image:didFinishSavingWithError:contextInfo:), nil);
    
    
    UIGraphicsEndImageContext();

    
    // Clean up
    free(data);
    CFRelease(ref);
    CFRelease(colorspace);
    CGImageRelease(iref);
    
    return image;
}

glGenTextures(1, &texture);
glBindTexture(GL_TEXTURE_2D, texture);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA4, width, height, 0, GL_RGBA, GL_UNSIGNED_BYTE, NULL);

glGenFramebuffers(1, &resolved_framebuffer);
glBindFramebuffer(GL_FRAMEBUFFER, resolved_framebuffer);
glGenRenderbuffers(1, &resolvedColorRenderbuffer);
glBindRenderbuffer(GL_RENDERBUFFER, resolvedColorRenderbuffer);
glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, texture, 0);

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

glGenRenderbuffers(1, &colorRenderbuffer);
glBindRenderbuffer(GL_RENDERBUFFER, colorRenderbuffer);
glRenderbufferStorageMultisampleAPPLE(GL_RENDERBUFFER, 4, GL_RGBA8_OES, width, height);
glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_RENDERBUFFER, colorRenderbuffer);

glGenRenderbuffers(1, &depthRenderbuffer);
glBindRenderbuffer(GL_RENDERBUFFER, depthRenderbuffer);
glRenderbufferStorageMultisampleAPPLE(GL_RENDERBUFFER, 4, GL_DEPTH_COMPONENT16, width, height);
glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_DEPTH_ATTACHMENT, GL_RENDERBUFFER, depthRenderbuffer);

GLenum status = glCheckFramebufferStatus(GL_FRAMEBUFFER) ;
if(status != GL_FRAMEBUFFER_COMPLETE) {
NSLog(@"failed to make complete framebuffer object %x", status);
}

// Render my scene

glBindFramebuffer( GL_FRAMEBUFFER, framebuffer );
glViewport(0,0,width,height);
glClear( GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT );

// Draw scene

// Then bind default framebuffer

glBindFramebuffer( GL_FRAMEBUFFER, 1 );

// Draw other things

// Now resolve the multisampling into the other fbo

glBindFramebuffer( GL_READ_FRAMEBUFFER_APPLE, framebuffer );
glBindFramebuffer( GL_DRAW_FRAMEBUFFER_APPLE, resolved_framebuffer );

glResolveMultisampleFramebufferAPPLE();

glUseTexture( GL_TEXTURE_2D, texture );

// Draw with texture