在可缩放的视图上绘图

Question

我正在研究一个小型绘图应用程序，它具有支持放大/缩小的基本要求。 我有两个主要问题：

1. 当视图被缩放/变换时，绘图不会显得清晰明朗。 是否有更好的方法，或者在缩放视图时是否有办法改善绘图？

2. 在1200 x 1200 pts画布（在iPhone上）上绘图时，绘图性能很慢。 我有机会为大帆布尺寸改进吗？

缩放代码：

- (void)scale:(UIPinchGestureRecognizer *)gestureRecognizer {
    [self adjustAnchorPointForGestureRecognizer:gestureRecognizer];

    UIView *canvas = [gestureRecognizer view];

    if ([gestureRecognizer state] == UIGestureRecognizerStateBegan ||
        [gestureRecognizer state] == UIGestureRecognizerStateChanged) {

        // Calculate the drawing view's size
        CGSize drawingViewSize = ...;

        // Calculate the minimum allowed tranform size
        // Developer's Note: I actually wanted to use the size 1/4th of the view
        // but self.view.frame.size doesn't return the correct (actual) width and height
        // It returns these values inverted i.e. width as height, and vice verse.
        // The reason is that the view appears to be transformed (90 degrees).
        // Since there's no work-around this, so for now, I'm just using fixed values.
        CGSize minTranformSize = CGSizeMake(100.0f, 100.0f);

        if ((minTranformSize.width > drawingViewSize.width) && (minTranformSize.height > drawingViewSize.height)) {
            minTranformSize = drawingViewSize;
        }

        // Transform the view, provided
        // 1. It won't scale more than the original size of the background image
        // 2. It won't scale less than the minimum possible transform
        CGSize transformedSize = CGSizeMake(canvas.frame.size.width * [gestureRecognizer scale],
                                            canvas.frame.size.height * [gestureRecognizer scale]);

        if ((transformedSize.width <= drawingViewSize.width) && (transformedSize.height <= drawingViewSize.height) &&
            (transformedSize.width >= minTranformSize.width) && (transformedSize.height >= minTranformSize.height)) {

            canvas.transform = CGAffineTransformScale([canvas transform],
                                                      [gestureRecognizer scale],
                                                      [gestureRecognizer scale]);
        }

        [gestureRecognizer setScale:1.0];

    } else if ([gestureRecognizer state] == UIGestureRecognizerStateEnded) {

        // Recenter the container view, if required (piece is smaller than the view and it's not aligned)
        CGSize viewSize = self.view.bounds.size;

        if ((canvas.frame.size.width < viewSize.width) ||
            (canvas.frame.size.height < viewSize.height)) {

            canvas.center = CGPointMake(viewSize.width/2, viewSize.height/2);
        }

        // Adjust the x/y coordinates, if required (piece is larger than the view and it's moving outwards from the view)
        if (((canvas.frame.origin.x > 0) || (canvas.frame.origin.y > 0)) &&
            ((canvas.frame.size.width >= viewSize.width) && (canvas.frame.size.height >= viewSize.height))) {

            canvas.frame = CGRectMake(0.0,
                                      0.0,
                                      canvas.frame.size.width,
                                      canvas.frame.size.height);
        }

        canvas.frame = CGRectIntegral(canvas.frame);
    }
}

绘图代码

- (void)draw {
    CGContextRef context = UIGraphicsGetCurrentContext();
    CGContextSaveGState(context);

    if (self.fillColor) {
        [self.fillColor setFill];
        [self.path fill];
    }

    if ([self.strokeColor isEqual:[UIColor clearColor]]) {
        [self.path strokeWithBlendMode:kCGBlendModeClear alpha:1.0];

    } else if (self.strokeColor) {
        [self.strokeColor setStroke];
        [self.path stroke];
    }

    CGContextRestoreGState(context);
}

Answer 1

这是一个非常复杂的问题，我一直在努力。

我最终将图纸转换为矢量。

1. 在一个图层中绘制所有线条，在另一个图层中绘制所有填充。
2. 使用potrace将线图转换为Vector（ http://potrace.sourceforge.net/ ）
3. 使用SVGKit（ https://github.com/SVGKit/SVGKit ）绘制矢量并隐藏1）中绘制的图层

它工作得非常好而且相当快，但它需要大量的工作。 我们公司的应用程序采用了这种技术：

https://itunes.apple.com/us/app/ideal-paint-hd-mormor/id569450492?mt=8 。

如果您唯一的问题是性能，请尝试查看CATiledLayer 。 （也用于上面提到的应用程序）。 它将极大地提高性能（你可以在这里找到一个非常好的教程http://www.cimgf.com/2011/03/01/subduing-catiledlayer/ ）。

祝好运！ :)

Answer 2

首先你是转换视图这不是更好的缩放方式。转换可能仅用于增加或减小UIVew的大小。对于缩放，你可以这样做。

1）使用此代码获取屏幕图片

UIGraphicsBeginImageContext(self.drawingView.bounds.size);
CGContextRef context = UIGraphicsGetCurrentContext();
//[self.view.layer renderInContext:context];
[self.layerContainerView.layer renderInContext:context];
UIImage *screenShot = UIGraphicsGetImageFromCurrentImageContext();
[scaleLabel setHidden:FALSE];
return screenShot;

2）然后将它放在一些UIImageView上，然后在这个图像上执行Zomming

 scrollView.userInteractionEnabled=TRUE;
self.scrollView.minimumZoomScale = 1.000;
self.scrollView.maximumZoomScale = 30.0f;
[self centerScrollViewContents];
CGFloat newZoomScale = self.scrollView.zoomScale / 1.5f;
newZoomScale = MAX(newZoomScale, self.scrollView.minimumZoomScale);
[self.scrollView setZoomScale:newZoomScale animated:YES];

3）然后再次在uiView的背景上设置缩放图像

这对我来说很完美，希望这对你也有用