Question

我有两个NSImage实例。我希望image2放在image1的顶部，具有一定的不透明度。它们具有匹配的尺寸。这些图像都不需要在UI中可见。

如何正确设置图形上下文并向其中绘制图像，一个具有完全不透明度，另一个是半透明的？

我一直在阅读这里的几个答案，但我发现它很复杂，特别是因为大多数似乎是针对Objective-C或仅适用于iOS。任何指针都是适用的。如果可以完成这一点而不需要一个更好的CGContext。

func blendImages(image1: NSImage, image2: NSImage, alpha: CGFloat) -> CGImage {

    // Create context
    var ctx: CGContextRef = CGBitmapContextCreate(0, inputImage.size.width, inputImage.size.height, 8, inputImage.size.width*4, NSColorSpace.genericRGBColorSpace(), PremultipliedLast)
    let area = CGRectMake(0, 0, inputImage.size.width, inputImage.size.height)
    CGContextScaleCTM(ctx, 1, -1)

    // Draw image1 in context

    // Draw image2 with alpha opacity
    CGContextSetAlpha(ctx, CGFloat(0.5))

    // Create CGImage from context
    let outputImage = CGBitmapContextCreateImage(ctx)

    return outputImage
}

在其他地方，我有这个扩展来从我的NSImages中获取CGImages：

extension NSImage {
    var CGImage: CGImageRef {
        get {
            let imageData = self.TIFFRepresentation
            let source = CGImageSourceCreateWithData(imageData as! CFDataRef, nil)
            let maskRef = CGImageSourceCreateImageAtIndex(source, 0, nil)
            return maskRef
        }
    }
}

Answer 1

我设法用NSGraphicsContext解决了这个问题。

func mergeImagesAB(pathA: String, pathB: String, fraction: CGFloat) -> CGImage {

    guard let imgA = NSImage(byReferencingFile: pathA),
         let imgB = NSImage(byReferencingFile: pathB),
         let bitmap = imgA.representations[0] as? NSBitmapImageRep,
         let ctx = NSGraphicsContext(bitmapImageRep: bitmap)
         else {fatalError("Failed to load images.")}

    let rect = NSRect(origin: CGPoint(x: 0, y: 0), size: bitmap.size)

    NSGraphicsContext.saveGraphicsState()
    NSGraphicsContext.setCurrentContext(ctx)
    imgB.drawInRect(rect, fromRect: rect, operation: .CompositeSourceOver, fraction: fraction)
    NSGraphicsContext.restoreGraphicsState()

    guard let result = bitmap.CGImage
        else {fatalError("Failed to create image.")}

    return result;
}

Answer 2

感谢Henrik，我需要Obj-C。如果有人也需要这个版本：

-(CGImageRef) mergeImage:(NSImage*)a andB:(NSImage*)b fraction:(float)fraction{
    NSBitmapImageRep *bitmap = (NSBitmapImageRep*)[[a representations] objectAtIndex:0];
    NSGraphicsContext *ctx = [NSGraphicsContext graphicsContextWithBitmapImageRep:bitmap];
    [NSGraphicsContext saveGraphicsState];
    [NSGraphicsContext setCurrentContext:ctx];

    CGRect rect = CGRectMake(0, 0, bitmap.size.width, bitmap.size.height);
    [NSGraphicsContext saveGraphicsState];
    [NSGraphicsContext setCurrentContext:ctx];
    [b drawInRect:rect fromRect:rect operation:NSCompositeSourceOver fraction:fraction];
    [NSGraphicsContext restoreGraphicsState];

    return [bitmap CGImage];
}

在OS X上使用Swift混合两个NSImages

2 个答案: