Draw new image on top of existing image in UIImageView

Vote count:

0

I'm trying to draw an image on top of an existing image in a UIImageView. The new image is from a png file that I load into a UIImage. I want to display that semi-transparently. I've played around with various core graphics APIs and can't get it to work. Also, the new image is much higher resolution than the current image displayed in the UIImageView, and I also want to offset it a bit when I draw it. Can someone please point me in the right direction?

The code below is my latest version. When I call this, nothing happens. In this code, imgView is the image view I'm drawing into, and newImage is the UIImage containing the higher resolution image I want to overlay on top of the image view. Not shown is the code I also need to offset the new image, in the code below, I'm just trying to draw it at 0, 0.

        UIImage* image = imgView.image;
        CGRect r;
        r.origin = CGPointZero;
        r.size = image.size;
        CGFloat scaleFactor = r.size.width * 1.0 / newImage.size.width;


            UIGraphicsBeginImageContext(r.size);

            // draw original image into the context
            [image drawAtPoint:CGPointZero];

            // get the context for CoreGraphics
            CGContextRef ctx = UIGraphicsGetCurrentContext();
            CGContextScaleCTM(ctx, scaleFactor, -1.0 * scaleFactor);
            CGContextTranslateCTM(ctx, 0, r.size.height);


            CGContextBeginTransparencyLayer(ctx, nil);
            CGContextSetAlpha(ctx, .25);
            CGContextDrawImage(ctx, r, CGImageCreateWithImageInRect(newImage.CGImage, r));
            CGContextEndTransparencyLayer(ctx);

            // make image out of bitmap context
            UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();

            // free the context
            UIGraphicsEndImageContext();
            [imgView setImage: newImage];

asked 38 secs ago

Dave

11