I've recently asked a question about clipping an image via path at view's drawRect method.

http://stackoverflow.com/questions/2570653/iphone-clip-image-with-path

Krasnyk's code is copied below.

- (void)drawRect:(CGRect)rect {
    CGContextRef context = UIGraphicsGetCurrentContext();
    CGMutablePathRef path = CGPathCreateMutable();
//or for e.g. CGPathAddRect(path, NULL, CGRectInset([self bounds], 10, 20));
    CGPathAddEllipseInRect(path, NULL, [self bounds]);
    CGContextAddPath(context, path);
    CGContextClip(context);
    CGPathRelease(path);
    [[UIImage imageNamed:@"GC.png"] drawInRect:[self bounds]];
}

It works very well. However, when my image is larger than the view itself, how do I show different parts of the image?

I tried tweaking around with translation on the locations (show as bounds above) of ellipse and/or UIImage drawInRect but some complex effects (Unwanted clipping, weird elipse size) I can't explain happens.