在 UIImage 周围添加透明空间答案

【问题标题】：Add transparent space around a UIImage在 UIImage 周围添加透明空间
【发布时间】：2013-11-16 17:31:18
【问题描述】：

假设我们有一个 600X400 像素的图像，我们希望最终得到一个 1000x1000 像素的新图像，其中包含中心的初始图像和它周围的透明空间。如何在代码中实现这一点？

【问题讨论】：

国际海事组织不应关闭。问题定义明确并且很有用。

【解决方案1】：

在 Swift 中，您可以为 UIImage 编写一个扩展来绘制带有插图的图像。

Swift 3：

import UIKit

extension UIImage {
    func imageWithInsets(insets: UIEdgeInsets) -> UIImage? {
        UIGraphicsBeginImageContextWithOptions(
            CGSize(width: self.size.width + insets.left + insets.right,
                   height: self.size.height + insets.top + insets.bottom), false, self.scale)
        let _ = UIGraphicsGetCurrentContext()
        let origin = CGPoint(x: insets.left, y: insets.top)
        self.draw(at: origin)
        let imageWithInsets = UIGraphicsGetImageFromCurrentImageContext()
        UIGraphicsEndImageContext()
        return imageWithInsets
    }
}

老答案：

import UIKit

extension UIImage {
    func imageWithInsets(insets: UIEdgeInsets) -> UIImage {
        UIGraphicsBeginImageContextWithOptions(
            CGSizeMake(self.size.width + insets.left + insets.right,
                self.size.height + insets.top + insets.bottom), false, self.scale)
        let context = UIGraphicsGetCurrentContext()
        let origin = CGPoint(x: insets.left, y: insets.top)
        self.drawAtPoint(origin)
        let imageWithInsets = UIGraphicsGetImageFromCurrentImageContext()
        UIGraphicsEndImageContext()
        return imageWithInsets
    }
}

【讨论】：

知道为什么有时这可能会返回 nil 吗？
参见developer.apple.com/reference/uikit/…：仅当基于位图的图形上下文是当前图形上下文时，才应调用此函数。如果当前上下文为 nil 或不是通过调用 UIGraphicsBeginImageContext(_:) 创建的，则此函数返回 nil。
@mixel 只是一个小建议：它应该是return imageWithInsets?.withRenderingMode(renderingMode) 以便也支持模板图像

【解决方案2】：

这是 Swift 4 中受 DrummerB 答案启发的解决方案：

import UIKit

extension UIImage {

    func addImagePadding(x: CGFloat, y: CGFloat) -> UIImage? {
        let width: CGFloat = size.width + x
        let height: CGFloat = size.height + y
        UIGraphicsBeginImageContextWithOptions(CGSize(width: width, height: height), false, 0)
        let origin: CGPoint = CGPoint(x: (width - size.width) / 2, y: (height - size.height) / 2)
        draw(at: origin)
        let imageWithPadding = UIGraphicsGetImageFromCurrentImageContext()
        UIGraphicsEndImageContext()

        return imageWithPadding
    }
}

如何申请：

let image = UIImage(named: "your-image")!
let imageView = UIImageView(image: image.addImagePadding(x: 50, y: 50))
imageView.backgroundColor = UIColor.gray
view.addSubview(imageView)

特点：

只需通过参数传递填充值
彩色填充（通过将 UIGraphicsBeginImageContextWithOptions 不透明参数设置为 false）

【讨论】：

【解决方案3】：

您创建一个 1000x1000 的新图像上下文，在中间绘制旧图像，然后从上下文中获取新的 UIImage。

// Setup a new context with the correct size
CGFloat width = 1000;
CGFloat height = 1000;
UIGraphicsBeginImageContextWithOptions(CGSizeMake(width, height), NO, 0.0);        
CGContextRef context = UIGraphicsGetCurrentContext();       
UIGraphicsPushContext(context);                             

// Now we can draw anything we want into this new context.
CGPoint origin = CGPointMake((width - oldImage.size.width) / 2.0f,
                            (height - oldImage.size.height) / 2.0f);
[oldImage drawAtPoint:origin];

// Clean up and get the new image.
UIGraphicsPopContext();                             
UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();

【讨论】：

亲爱的鼓手 B！非常感谢您发布有效的解决方案。唯一的修正是替换 CGPoint origin = CGRectMake((width - oldImage.size.width) / 2.0f, (height - oldImage.size.height) / 2.0f); with CGPoint origin = CGPointMake((width - oldImage.size.width) / 2.0f, (height - oldImage.size.height) / 2.0f);
@DrummerB 你不希望UIGraphicsBeginImageContextWithOptions 中的opaque 参数为NO，因为他想要透明空间吗？

【解决方案4】：

在 UIImage 上创建一个类别并试试这个：

+ (UIImage *)imageWithInsets:(CGRect)insetRect image:(UIImage *)image {
    CGRect newRect = CGRectMake(0.0, 0.0, insetRect.origin.x+insetRect.size.width+image.size.width, insetRect.origin.y+insetRect.size.height+image.size.height);
    // Setup a new context with the correct size
    UIGraphicsBeginImageContextWithOptions(newRect.size, NO, 0.0);
    CGContextRef context = UIGraphicsGetCurrentContext();
    UIGraphicsPushContext(context);

    // Now we can draw anything we want into this new context.
    CGPoint origin = CGPointMake(insetRect.origin.x, insetRect.origin.y);
    [image drawAtPoint:origin];

    // Clean up and get the new image.
    UIGraphicsPopContext();
    UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return newImage;
}

【讨论】：

【解决方案5】：

通过更好的命名约定修复了 appsunited 的答案。为了不混淆它，函数是否正在变异：

extension UIImage {
    func withPadding(_ padding: CGFloat) -> UIImage? {
        return withPadding(x: padding, y: padding)
    }

    func withPadding(x: CGFloat, y: CGFloat) -> UIImage? {
        let newWidth = size.width + 2 * x
        let newHeight = size.height + 2 * y
        let newSize = CGSize(width: newWidth, height: newHeight)
        UIGraphicsBeginImageContextWithOptions(newSize, false, 0)
        let origin = CGPoint(x: (newWidth - size.width) / 2, y: (newHeight - size.height) / 2)
        draw(at: origin)
        let imageWithPadding = UIGraphicsGetImageFromCurrentImageContext()
        UIGraphicsEndImageContext()

        return imageWithPadding
    }
}

【讨论】：