Question

我使用本教程中的绘图代码让某人在一个小方框中绘图：http://www.ifans.com/forums/showthread.php?t=132024

默认代码在整个屏幕上绘制，如何将绘图限制在屏幕上的小方框中？

Answer 1

在此示例中，触摸和绘图发生在视图控制器的主视图中：

UIGraphicsBeginImageContext(self.view.frame.size);
[drawImage.image drawInRect:CGRectMake(0, 0, self.view.frame.size.width, self.view.frame.size.height)];

等...

因此，如果您将该视图的框架更改为较小的尺寸，则应自动将图形限制为较小的尺寸。

或者您可以将触摸识别和绘图“移动”到另一个较小的子视图中：

创建一个新的较小的子视图。
将其添加到主视图中。
将UITapGestureRecognizer添加到小视图
处理UITapGestureRecognizer操作中的触摸并在子视图上执行绘图。

=====编辑=====

以下是如何操作：

- (void)viewDidLoad{
   [super viewDidLoad];
   self.view.backgroundColor = [UIColor grayColor];

   canvas = [[UIView alloc] initWithFrame:CGRectMake(200.0, 200.0, 300.0, 300.0)];
   canvas.backgroundColor = [UIColor whiteColor];
   [self.view addSubview:canvas];

   UIImageView *iv = [[UIImageView alloc] initWithImage:nil];
   iv.frame = canvas.frame;
   [self.view addSubview:iv];
   self.drawImage = iv;
   [iv release];

   UIPanGestureRecognizer *panRec = [[UIPanGestureRecognizer alloc] initWithTarget:self action:@selector(userPanned:)];
   [canvas addGestureRecognizer:panRec];    
   [panRec release];
}


- (void)userPanned:(UIPanGestureRecognizer *)recognizer {
   CGPoint touchPoint = [recognizer locationInView:canvas];

   if (recognizer.state == UIGestureRecognizerStateBegan) lastTouchPoint = touchPoint;

      if (CGRectContainsPoint(CGRectMake(0.0, 0.0, canvas.frame.size.width, canvas.frame.size.height), touchPoint)) {
         UIGraphicsBeginImageContext(canvas.frame.size);
         [drawImage.image drawInRect:CGRectMake(0.0, 0.0, canvas.frame.size.width, canvas.frame.size.height)];
         CGContextSetLineCap(UIGraphicsGetCurrentContext(), kCGLineCapRound);
         CGContextSetLineWidth(UIGraphicsGetCurrentContext(), 5.0);
         CGContextSetRGBStrokeColor(UIGraphicsGetCurrentContext(), 1.0, 0.0, 0.0, 1.0);
         CGContextBeginPath(UIGraphicsGetCurrentContext());
         CGContextMoveToPoint(UIGraphicsGetCurrentContext(), lastTouchPoint.x, lastTouchPoint.y);
         CGContextAddLineToPoint(UIGraphicsGetCurrentContext(), touchPoint.x, touchPoint.y);
         CGContextStrokePath(UIGraphicsGetCurrentContext());
         drawImage.image = UIGraphicsGetImageFromCurrentImageContext();
         UIGraphicsEndImageContext();

         lastTouchPoint = touchPoint;
     }
}

canvas，lastTouchPoint和drawImage是iVars。

我没有实现doubleTap和Tap例程来清除图像并绘制一个点，但这应该足以让你开始。

如何限制绘图区域？

1 个答案: