>>452
半径だけで判定の場合

- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event
{
　CGPoint p = [[touches anyObject] locationInView:self];
　CGFloat w = self.bounds.size.width;
　CGFloat h = self.bounds.size.height;

　CGFloat targetRadius = w * 0.7 * 0.5;
　 CGPoint targetCenter = CGPointMake(w/2, h/2);

　//pとtargetCenterの距離がtargetRadius以下ならHit!!
　CGFloat r = sqrt(pow(p.x - targetCenter.x, 2.0) + pow(p.y - targetCenter.y, 2.0));
　if (r <= targetRadius) { NSLog(@"Hit!!"); }
}