在iPad中用手指移动响应缓慢

Question

下面的代码工作但响应非常慢，我无法用快速手指移动绘制。我认为我的子视图“TestView”是它的一个原因，但它是我的应用程序的基本要求。

在HomeView.h文件中

IBOutlet UIImageView *imgDraw;
IBOutlet UIView *TestView;

@private
    CGPoint currentPoint;
    CGPoint previousPoint1;
    CGPoint previousPoint2;

这里我使用TestView作为HomeView中的子视图在TestView中绘制，这里imgDraw存在于TestView中。

在HomeView.m文件中

- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event 
{
    mouseSwiped = YES;

    UITouch *touch = [touches anyObject];   
    currentPoint = [touch locationInView:TestView];

    previousPoint2 = previousPoint1;
    previousPoint1 = [touch previousLocationInView:self.view];
    currentPoint = [touch locationInView:self.view];

    // calculate mid point.
    CGPoint mid1 = midPoint(previousPoint1, previousPoint2); 
    CGPoint mid2 = midPoint(currentPoint, previousPoint1);
    UIGraphicsBeginImageContext(TestView.frame.size);
    [imgDrawAlphaPad.image drawInRect:CGRectMake(0, 0, self.TestView.frame.size.width, self.TestView.frame.size.height)];
    CGContextSetLineCap(UIGraphicsGetCurrentContext(), kCGLineCapRound);

    //NSLog(@"iPhone");
    //CGContextSetLineWidth(UIGraphicsGetCurrentContext(), [appDelegate_iPhone.StrokeWidth floatValue]);
    CGContextSetLineWidth(UIGraphicsGetCurrentContext(), 2);
    CGContextSetRGBStrokeColor(UIGraphicsGetCurrentContext(), 1, 0, 0, 0.9);
    CGContextBeginPath(UIGraphicsGetCurrentContext());

    //Code for smooth drawing.{#DR#-12/05/2012}
    CGContextMoveToPoint(UIGraphicsGetCurrentContext(), mid1.x, mid1.y);

    // Use QuadCurve is the key
    CGContextAddQuadCurveToPoint(UIGraphicsGetCurrentContext(), previousPoint1.x, previousPoint1.y, mid2.x, mid2.y); 

    CGContextStrokePath(UIGraphicsGetCurrentContext());
    //CGContextFlush(UIGraphicsGetCurrentContext());

    drawImage.image = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    lastPoint = currentPoint;
}

CGPoint midPoint(CGPoint p1, CGPoint p2)
{
    return CGPointMake((p1.x + p2.x) * 0.5, (p1.y + p2.y) * 0.5);   
}