Take snapshot of the CCGLView

Question

I want to take snapshot of the content in CCGLView in my viewController and display the resultant image in the same viewController.

Right now I'm using the following method to do so :

-(UIImage *) drawableToCGImage{
    GLint backingWidth2, backingHeight2;
    //backingHeight2=self.glView.frame.size.height;
    //backingWidth2=self.glView.frame.size.width;
    //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, self.glView.colorRenderBuffer);

    // Get the size of the backing CAEAGLLayer
    glGetRenderbufferParameterivOES(GL_RENDERBUFFER_OES, GL_RENDERBUFFER_WIDTH_OES, &backingWidth2);
    glGetRenderbufferParameterivOES(GL_RENDERBUFFER_OES, GL_RENDERBUFFER_HEIGHT_OES, &backingHeight2);

    NSInteger x = self.glView.frame.origin.x, y = self.glView.frame.origin.y, width2 = backingWidth2, height2 = backingHeight2;
    NSInteger dataLength = width2 * height2 * 4;
    GLubyte *data = (GLubyte*)malloc(dataLength * sizeof(GLubyte));

    // Read pixel data from the framebuffer
    glPixelStorei(GL_PACK_ALIGNMENT, 4);
    glReadPixels(x, y, width2, height2, 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(width2, height2, 8, 32, width2 * 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;

    // 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 = self.glView.contentScaleFactor;
    widthInPoints = width2 / scale;
    heightInPoints = height2 / scale;
    UIGraphicsBeginImageContextWithOptions(CGSizeMake(widthInPoints, heightInPoints), NO, scale);


    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();

    UIGraphicsEndImageContext();

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

    return image;
}    

But it works only in simulator and in device when I test it, I don't get the content of the CCGLView. Why this method doesn't give the snapshot in device? Or is there any other way to get it done?

Answer 1

I don't know why the previous method didn't work, but I got to know another way of doing it, and its less expensive too :). I'm using the following method :

- (UIImage *)snapshot:(UIView *)view{
UIGraphicsBeginImageContextWithOptions(view.bounds.size, YES, 0);
[view drawViewHierarchyInRect:view.bounds afterScreenUpdates:YES];
UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();

return image;

}

for more info go to following link: https://developer.apple.com/library/ios/qa/qa1817/_index.html