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我正在使用Ray Wenderlich 的教程中分享的想法使用 UIKit 开发简单的绘图应用程序。不同之处在于我需要实现一个功能，以便我可以缩放/缩放到我的绘图并绘制更细的线条。我可以使用 CGAffineTransformScale 放大（当然还有 UIPinchGestureRecognizer）并使用 CGAffineTransform 在 UIImage 周围移动 - 问题是一旦放大检测到的 UITouch 点，实际的触摸点就会有很大的偏移。随着我不断缩放图像，这个偏移量变得更大。

在代码中

drawingImage - 用户与
SavingImage 交互的一个 - 保存绘制的线条
transform_translate - CGAffinetransform
lastScale - CGFloat 保存最后一个缩放比例值
lastPoint - CGPoint 保存最后一个触摸点
lastPointForPinch - CGPoint 保存最后一个捏点

捏合手势在 viewDidLoad 中初始化为 -

pinchGestureRecognizer = [[UIPinchGestureRecognizer alloc] initWithTarget:self action:@selector(pinchGestureDetected:)];
[self.drawingImage addGestureRecognizer:pinchGestureRecognizer];

UIPinchGesture 检测的方法是——

- (void)pinchGestureDetected:(UIPinchGestureRecognizer *)recognizer
{
    
    if([recognizer state] == UIGestureRecognizerStateBegan) {
        // Reset the last scale, necessary if there are multiple objects with different scales
        
        lastScale = [recognizer scale];
        lastPointForPinch = [recognizer locationInView:self.drawingImage];
        
    }
    
    if ([recognizer state] == UIGestureRecognizerStateBegan ||
        [recognizer state] == UIGestureRecognizerStateChanged) {
        
        CGFloat currentScale = [[[recognizer view].layer valueForKeyPath:@"transform.scale"] floatValue];
        
        // Constants to adjust the max/min values of zoom
        const CGFloat kMaxScale = 2.0;
        const CGFloat kMinScale = 1.0;
        
        CGFloat newScale = 1 -  (lastScale - [recognizer scale]);
        newScale = MIN(newScale, kMaxScale / currentScale);
        newScale = MAX(newScale, kMinScale / currentScale);
        
        CGAffineTransform transform = CGAffineTransformScale([[recognizer view] transform], newScale, newScale);

        self.savingImage.transform = transform;
        self.drawingImage.transform=transform;
        
        lastScale = [recognizer scale];  // Store the previous scale factor for the next pinch gesture call
        
        CGPoint point = [recognizer locationInView:self.drawingImage];
        transform_translate = CGAffineTransformTranslate([[recognizer view] transform], point.x - lastPointForPinch.x, point.y - lastPointForPinch.y);
        
        self.savingImage.transform = transform_translate;
        self.drawingImage.transform=transform_translate;
        lastPointForPinch = [recognizer locationInView:self.drawingImage];
        
    }
}

画线的方法（仅供参考，这是取自上述教程的一个相当标准的过程，如果我在这里犯了一些错误，可以把它放在这里） -

- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {
    mouseSwiped = NO;
    UITouch *touch = [touches anyObject];
    lastPoint = [touch locationInView:self.drawingImage];
    UIGraphicsBeginImageContext(self.savingImage.frame.size);
}
- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event {
    mouseSwiped = YES;
    UITouch *touch = [touches anyObject];
    CGPoint currentPoint = [touch locationInView:self.drawingImage];
    CGContextRef ctxt = UIGraphicsGetCurrentContext();
    CGContextMoveToPoint(ctxt, lastPoint.x, lastPoint.y);
    CGContextAddLineToPoint(ctxt, currentPoint.x, currentPoint.y);
    CGContextSetLineCap(ctxt, kCGLineCapRound);
    CGContextSetLineWidth(ctxt, brush );
    CGContextSetRGBStrokeColor(ctxt, red, green, blue, opacity);
    CGContextSetBlendMode(ctxt,kCGBlendModeNormal);
    CGContextSetShouldAntialias(ctxt,YES);
    CGContextSetAllowsAntialiasing(ctxt, YES);
    CGContextStrokePath(ctxt);   
    self.drawingImage.image = UIGraphicsGetImageFromCurrentImageContext();
    lastPoint = currentPoint;
      
}
- (void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event {
    if(!mouseSwiped) {
        UIGraphicsEndImageContext();
        UITouch *touch = [touches anyObject];
        CGPoint currentPoint = [touch locationInView:self.drawingImage];
        UIGraphicsBeginImageContext(self.drawingImage.frame.size);
        CGContextSetLineCap(UIGraphicsGetCurrentContext(), kCGLineCapRound);
        CGContextSetLineWidth(UIGraphicsGetCurrentContext(), brush);
        CGContextSetRGBStrokeColor(UIGraphicsGetCurrentContext(), red, green, blue, opacity);
        CGContextMoveToPoint(UIGraphicsGetCurrentContext(), lastPoint.x, lastPoint.y);
        CGContextAddLineToPoint(UIGraphicsGetCurrentContext(), currentPoint.x, currentPoint.y);
        CGContextStrokePath(UIGraphicsGetCurrentContext());
        self.drawingImage.image = UIGraphicsGetImageFromCurrentImageContext();
        [self.drawingImage.image drawInRect:CGRectMake(0, 0, self.drawingImage.frame.size.width, self.drawingImage.frame.size.height) blendMode:kCGBlendModeNormal alpha:1.0];
        
    }
    UIGraphicsEndImageContext();
    UIGraphicsBeginImageContext(self.savingImage.frame.size);
    [self.savingImage.image drawInRect:CGRectMake(0, 0, self.savingImage.frame.size.width, self.savingImage.frame.size.height) blendMode:kCGBlendModeNormal alpha:1.0];
    [self.drawingImage.image drawInRect:CGRectMake(0, 0, self.drawingImage.frame.size.width, self.drawingImage.frame.size.height) blendMode:kCGBlendModeNormal alpha:1.0];
    self.savingImage.image = UIGraphicsGetImageFromCurrentImageContext();
    self.drawingImage.image=nil;
    UIGraphicsEndImageContext();
    
    }
}

我试过做 CGPointApplyAffineTransform(point, transform_translate) 但巨大的偏移量仍然存在。

希望我的问题得到了清楚的解释，有人可以帮助我。我一直在努力在这方面取得进展。提前致谢

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1 回答 1

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我终于找到了解决方案……一次又一次地犯了一个愚蠢的错误。locationInView 需要来自 self.view 而不是来自图像。

@davidkonard 感谢您的建议-实际上我没有意识到（在绘图应用程序的上下文中）用户触摸屏幕的意图正是在那一点上绘图将完成，因此即使 UIImageView 被移动，用户仍然想要在他的手指下画一个点/线/任何东西。所以 locationInView 应该是 self.view （在我的例子中 self.view 从来没有改变过）。

希望这能解释为什么我会犯错误以及我是如何想出解决方案的。

于 2014-03-27T18:10:46.220 回答