Question

嗨就像我在标题上说的那样，我试图在一个与UIImage最大尺寸相匹配的正方形中绘制一个完整的UIImage。我的问题是如何使我的代码工作。什么我的代码下降是裁剪到正方形大小。我是IO的新手可以帮助。

我想要调用CGcontext的方法吗？

感谢。

- (UIImage*)imageWithBorderFromImage:(UIImage*)source;
{
    CGSize size = [source size];
    CGFloat width = size.width;
    CGFloat height = size.height;
    CGSize resizedImageSize;
    if (width < height) {
        resizedImageSize = CGSizeMake(height, height);
    }else {
        resizedImageSize = CGSizeMake(width, width);
    }
    UIGraphicsBeginImageContext(resizedImageSize);
    CGRect rect = CGRectMake(0, 0, resizedImageSize.width, resizedImageSize.height);
    [source drawInRect:rect blendMode:kCGBlendModeNormal alpha:1.0];

    CGContextRef context = UIGraphicsGetCurrentContext();
    CGContextSetRGBStrokeColor(context, 1.0, 0.5, 1.0, 1.0);
    CGContextStrokeRect(context, rect);
    UIImage *testImg =  UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return testImg;
}

我正在寻找的结果类型。

Answer 1

看起来你比实现自己的目标更接近了。调用drawInRect时需要调整使用的矩形：保持纵横比并适合新图像的中间位置。请记住，那里使用的rect没有规定新图像的大小，传递给UIGraphicsBeginImageContext的值定义了。

- (UIImage *)squareImageFromImage:(UIImage *)image
{
    // Get a square that the image will fit into
    CGFloat maxSize = MAX(image.size.height, image.size.width);
    CGSize squareSize = CGSizeMake(maxSize, maxSize);

    // Get our offset to center the image inside our new square frame
    CGFloat dx = (maxSize - image.size.width) / 2.0f;
    CGFloat dy = (maxSize - image.size.height) / 2.0f;

    UIGraphicsBeginImageContext(squareSize);
    CGRect rect = CGRectMake(0, 0, maxSize, maxSize);

    // Draw a white background and set a magenta stroke around the entire square image (debugging only?)
    CGContextRef context = UIGraphicsGetCurrentContext();
    CGContextSetFillColorWithColor(context, [UIColor whiteColor].CGColor);
    CGContextSetStrokeColorWithColor(context, [UIColor magentaColor].CGColor);
    CGContextFillRect(context, rect);
    CGContextStrokeRect(context, rect);

    // Adjust the rect to be centered in our new image
    rect = CGRectInset(rect, dx, dy);
    [image drawInRect:rect blendMode:kCGBlendModeNormal alpha:1.0];

    UIImage *squareImage =  UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();

    return squareImage;
}

采用此样本图像 Before Image, Rectangular

并为您提供这个新的方形图像 Processed Image, Square

Answer 2

在Swift 3中

extension UIImage {

    func squareMe() -> UIImage {

        var squareImage = self
        let maxSize = max(self.size.height, self.size.width)
        let squareSize = CGSize(width: maxSize, height: maxSize)

        let dx = CGFloat((maxSize - self.size.width) / 2)
        let dy = CGFloat((maxSize - self.size.height) / 2)

        UIGraphicsBeginImageContext(squareSize)
        var rect = CGRect(x: 0, y: 0, width: maxSize, height: maxSize)

        if let context = UIGraphicsGetCurrentContext() {
            context.setFillColor(UIColor.clear.cgColor)
            context.fill(rect)

            rect = rect.insetBy(dx: dx, dy: dy)
            self.draw(in: rect, blendMode: .normal, alpha: 1.0)

            if let img = UIGraphicsGetImageFromCurrentImageContext() {
                squareImage = img
            }
            UIGraphicsEndImageContext()

        }

        return squareImage
    }

}

如何在边缘为白色的正方形内绘制完整的UIImage

2 个答案: