How to take a snapshot of a MGLKView ?

[alfonsotesauro]

Hello, thanks to everybody for the attention.
I develop a iOS application that uses a SDK that uses the MetalAngle framework.
I need to capture the color of pixels on the frontmost view in my app. For standard UIViewControllers, I use simply:

• (UIColor *) GetCurrentPixelColorAtPoint:(CGPoint)point
  {
  unsigned char pixel[4] = {0};

  CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();

  CGContextRef context = CGBitmapContextCreate(pixel, 1, 1, 8, 4, colorSpace, kCGBitmapAlphaInfoMask & kCGImageAlphaPremultipliedLast);

  CGContextTranslateCTM(context, -point.x, -point.y);

  [self.view.layer renderInContext:context];

  CGContextRelease(context);

  CGColorSpaceRelease(colorSpace);

  NSLog(@"pixel: %d %d %d %d", pixel[0], pixel[1], pixel[2], pixel[3]);

  UIColor *color = [UIColor colorWithRed:pixel[0]/255.0 green:pixel[1]/255.0 blue:pixel[2]/255.0 alpha:pixel[3]/255.0];

  return color;
  }

If I try to make the same on my MGLKView I always get a clearColor, regardless of the appearance of the view. I know that point is not transparent, so there must be something weird going on. for MGLKView, I simply do the same:

• (UIColor *) GetCurrentPixelColorAtPoint:(CGPoint)point
  {
  unsigned char pixel[4] = {0};

  CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();

  CGContextRef context = CGBitmapContextCreate(pixel, 1, 1, 8, 4, colorSpace, kCGBitmapAlphaInfoMask & kCGImageAlphaPremultipliedLast);

  CGContextTranslateCTM(context, -point.x, -point.y);

  [self.glView.glLayer renderInContext:context];

  CGContextRelease(context);

  CGColorSpaceRelease(colorSpace);

  NSLog(@"pixel: %d %d %d %d", pixel[0], pixel[1], pixel[2], pixel[3]);

  UIColor *color = [UIColor colorWithRed:pixel[0]/255.0 green:pixel[1]/255.0 blue:pixel[2]/255.0 alpha:pixel[3]/255.0];

  return color;
  }

So the question is, if you don't want to read the code, how to take a UIImage or a UIColor of a pixel of a MGLKView on iOS ?

Thanks to everybody and sorry for the long message.

[myonlylonely]

I have replaced Ejecta's original OpenGLES implemention with MetalANGLE. Here is the code that takes a screenshot from MGLKView in Ejecta . Not precisely what you want.

EJCanvasContext *screenCanvasContext = scriptView.screenRenderingContext;
EJCanvasContextWebGLScreen *screenWebGLCanvasContext = (EJCanvasContextWebGLScreen*)screenCanvasContext;

UIGraphicsBeginImageContextWithOptions(CGSizeMake(CGRectGetWidth(screenWebGLCanvasContext.view.frame), CGRectGetHeight(screenWebGLCanvasContext.view.frame)), YES, 0.0);
[screenWebGLCanvasContext.view drawViewHierarchyInRect:screenWebGLCanvasContext.view.bounds afterScreenUpdates:NO];
UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();

if(image) {
    NSData *raw = UIImagePNGRepresentation(image);
}