Question

I’m trying to add images to table cells in a grouped UITableView but the corners of the images are not clipped. What’s the best way to go about clipping these (besides clipping them in Photoshop? The table contents are dynamic.)

For example, the first image in a table would need the top left corner rounded only.

Answer 1

This was my solution, which could use a little refactoring:

void addRoundedRectToPath(CGContextRef context, CGRect rect, float ovalWidth, float ovalHeight, BOOL top, BOOL bottom)
{
    float fw, fh;
    if (ovalWidth == 0 || ovalHeight == 0) {
        CGContextAddRect(context, rect);
        return;
    }
    CGContextSaveGState(context);
    CGContextTranslateCTM (context, CGRectGetMinX(rect), CGRectGetMinY(rect));
    CGContextScaleCTM (context, ovalWidth, ovalHeight);
    fw = CGRectGetWidth (rect) / ovalWidth;
    fh = CGRectGetHeight (rect) / ovalHeight;
    CGContextMoveToPoint(context, fw, fh/2);
    CGContextAddArcToPoint(context, fw, fh, fw/2, fh, 0);

    NSLog(@"bottom? %d", bottom);

    if (top) {
        CGContextAddArcToPoint(context, 0, fh, 0, fh/2, 3);
    } else {
        CGContextAddArcToPoint(context, 0, fh, 0, fh/2, 0);
    }

    if (bottom) {
        CGContextAddArcToPoint(context, 0, 0, fw/2, 0, 3);
    } else {
        CGContextAddArcToPoint(context, 0, 0, fw/2, 0, 0);
    }

    CGContextAddArcToPoint(context, fw, 0, fw, fh/2, 0);
    CGContextClosePath(context);
    CGContextRestoreGState(context);
}

- (UIImage *)roundCornersOfImage:(UIImage *)source roundTop:(BOOL)top roundBottom:(BOOL)bottom {
    int w = source.size.width;
    int h = source.size.height;

    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
    CGContextRef context = CGBitmapContextCreate(NULL, w, h, 8, 4 * w, colorSpace, kCGImageAlphaPremultipliedFirst);

    CGContextBeginPath(context);
    CGRect rect = CGRectMake(0, 0, w, h);
    addRoundedRectToPath(context, rect, 4, 4, top, bottom);
    CGContextClosePath(context);
    CGContextClip(context);

    CGContextDrawImage(context, CGRectMake(0, 0, w, h), source.CGImage);

    CGImageRef imageMasked = CGBitmapContextCreateImage(context);
    CGContextRelease(context);
    CGColorSpaceRelease(colorSpace);

    return [UIImage imageWithCGImage:imageMasked];    
}

Implement those functions, then check the indexPath in the cellForRowAtIndexPath delegate method to determine which corner to round.

if (indexPath.row == 0) {
            cell.imageView.image = [self roundCornersOfImage:coverImage roundTop:YES roundBottom:NO];
        } else if (indexPath.row == [indexPath length]) {
            cell.imageView.image = [self roundCornersOfImage:coverImage roundTop:NO roundBottom:YES];
        } else {
            cell.imageView.image = coverImage;
        }