我正在开发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 View 缩放/变换时，绘图显得不清晰。有没有更好的方法，或者有没有办法在 View 缩放时改进绘图？

2. 在 1200 x 1200 pts Canvas 上(在 iPhone 上)绘图时，绘图性能很慢。我有机会针对大 Canvas 尺寸改进它吗？

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);
}

最佳答案

这是一个相当复杂的问题，我一直在努力解决。

我最终将绘图转换为矢量。

1. 在一层中绘制所有线条，在另一层中绘制所有填充。
2. 使用 potrace ( http://potrace.sourceforge.net/ ) 将线条图转换为 Vector
3. 使用 SVGKit 绘制矢量 ( https://github.com/SVGKit/SVGKit ) 并隐藏 1) 中绘制的层

它运行良好且速度相当快，但需要大量工作。我们公司有一个应用程序应用了这种技术:

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。 (也用在上面提到的应用程序中)。它将极大地提高性能(您可以在此处找到非常好的教程 http://www.cimgf.com/2011/03/01/subduing-catiledlayer/ )。

祝你好运! :)

关于ios - 在可缩放 View 上绘图，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/18181707/