Question

is it possible to add an alpha property on a region in the same image?
For example

Answer 1

The easiest solution would be to break the image apart and save the alpha as part of a png, then organize the imageviews to be flush against each other.

Otherwise, I wrote this quick code in a regular view that does the same with an image (I’m relatively new to Core Graphics so I’m sure there are better ways of doing this – also, my example the images are side by side):

-(void) drawRect {

    // GET THE CONTEXT, THEN FLIP THE COORDS (my view is 189 ponts tall)

    CGContextRef context = UIGraphicsGetCurrentContext();
    CGAffineTransform flip = CGAffineTransformMake(1, 0, 0, -1, 0, 189);
    CGContextConcatCTM(context, flip);

    // GET THE IMAGE REF

    UIImage *targetImage = [UIImage imageNamed:@"test.jpg"];
    CGImageRef imageRef = targetImage.CGImage;

    // SET THE COORDS

    CGRect imageCoords = CGRectMake(0, 0, 116, 189);
    CGRect imageCoordsTwo = CGRectMake(116, 0, 117, 189);

    // CUT UP THE IMAGE INTO TWO IMAGES

    CGImageRef firstImage = CGImageCreateWithImageInRect(imageRef, imageCoords);
    CGImageRef secondImage = CGImageCreateWithImageInRect(imageRef, imageCoordsTwo);

    // DRAW FIRST IMAGE, SAVE THE STATE, THEN SET THE TRANSPARENCY AMOUNT

    CGContextDrawImage(context, imageCoords, firstImage);
    CGContextSaveGState(context);
    CGContextSetAlpha(context, .4f);

    // DRAW SECOND IMAGE, RESTORE THE STATE

    CGContextDrawImage(context, imageCoordsTwo, secondImage);
    CGContextRestoreGState(context);

    // TIDY UP

    CGImageRelease(firstImage);
    CGImageRelease(secondImage);

}