在两个轴上翻转NSImage

Question

我正在尝试翻转使用NSImageBitmapRep表示创建的NSImage。经过一些挖掘（Flipping Quicktime preview & capture和Mirroring CIImage/NSImage）后，我通过CIImage尝试了两种方法，并对两个因子应用了-1的缩放变换。

首先使用CIImage imageByApplyingTransform：

    NSBitmapImageRep *imgRep = ...
    CGImageRef cgi = [imgRep CGImage];
    CIImage *cii = [CIImage imageWithCGImage:cgi];
    CGAffineTransform at = CGAffineTransformTranslate(CGAffineTransformMakeScale(-1, -1), 0, 0);
    NSCIImageRep *ciiRep = [NSCIImageRep imageRepWithCIImage:[cii imageByApplyingTransform:at]];

    NSImage *img = [[[NSImage alloc] init] autorelease];
    [img addRepresentation:ciiRep];
    [self.ivImage setImage:img];

然后使用CIAffineTransform过滤器：

    NSBitmapImageRep *imgRep = ...
    CGImageRef cgi = [imgRep CGImage];
    CIImage *cii = [CIImage imageWithCGImage:cgi];
    CIFilter *f = [CIFilter filterWithName:@"CIAffineTransform"];
    NSAffineTransform *t = [NSAffineTransform transform];
    [t scaleXBy:1.0 yBy:1.0];
    //[t translateXBy:width yBy:0];
    [f setValue:t forKey:@"inputTransform"];
    [f setValue:cii forKey:@"inputImage"];
    CIImage *cii2 = [f valueForKey:@"outputImage"];
    NSCIImageRep *ciiRep = [NSCIImageRep imageRepWithCIImage:cii2];

    NSImage *img = [[[NSImage alloc] init] autorelease];
    [img addRepresentation:ciiRep];
    [self.ivImage setImage:img];

两种方式都会产生空白图像。我也尝试翻译图像，以防因为-1次缩放而出现在屏幕外，但无济于事。如果我使用正值进行缩放，我可以看到正确应用了变换。

self.ivImage是一个NSImageView。我想要一个翻转的实际NSImage，因此不应该将转换应用于NSImageView。

这是32位，Lion上的Xcode 4.3.2。

Answer 1

你应该初始化你的NSImage大小。

通过翻译展示您的尝试，因为这是正确的方式。通常，首先进行翻译然后进行缩放最容易。您的代码片段似乎有翻译尝试的残余痕迹，但它们并不正确。您在一个案例和宽度中翻译0,0，在另一个案例和宽度中翻译0。此外，在您的第二个代码段中，您缩放1,1（正），因此不会翻转。

此外，简单地将焦点锁定在适当大小的新图像上，设置变换并绘制图像代表可能更简单。用CIImage避免所有这些东西。

NSBitmapImageRep *imgRep = ...
NSImage* img = [[[NSImage alloc] initWithSize:NSMakeSize(imgRep.pixelsWide, imgRep.pixelsHigh)] autorelease];
[img lockFocus];
NSAffineTransform* t = [NSAffineTransform transform];
[t translateXBy:imgRep.pixelsWide yBy:imgRep.pixelsHigh];
[t scaleXBy:-1 yBy:-1];
[t concat];
[imgRep drawInRect:NSMakeRect(0, 0, imgRep.pixelsWide, imgRep.pixelsHigh)];
[img unlockFocus];

Answer 2

无论如何，我认为一个好主意应该是发布一个完整的功能。这是我基于Ken帖子的解决方案

- (NSImage *)flipImage:(NSImage *)image
{
    NSImage *existingImage = image;
    NSSize existingSize = [existingImage size];
    NSSize newSize = NSMakeSize(existingSize.width, existingSize.height);
    NSImage *flipedImage = [[[NSImage alloc] initWithSize:newSize] autorelease];

    [flipedImage lockFocus];
    [[NSGraphicsContext currentContext] setImageInterpolation:NSImageInterpolationHigh];

    NSAffineTransform *t = [NSAffineTransform transform];
    [t translateXBy:existingSize.width yBy:existingSize.height];
    [t scaleXBy:-1 yBy:-1];
    [t concat];

    [existingImage drawAtPoint:NSZeroPoint fromRect:NSMakeRect(0, 0, newSize.width, newSize.height) operation:NSCompositeSourceOver fraction:1.0];

    [flipedImage unlockFocus];

    return flipedImage;
}

Answer 3

用于垂直翻转

- (NSImage *)flipImageVertically:(NSImage *)inputImage {

    NSImage *tmpImage;
    NSAffineTransform *transform = [NSAffineTransform transform];

    NSSize dimensions = [inputImage size];
    NSAffineTransformStruct flip = {1.0, 0.0, 0.0, -1.0, 0.0,
        dimensions.height};
    tmpImage = [[NSImage alloc] initWithSize:dimensions];
    [tmpImage lockFocus];
    [transform setTransformStruct:flip];
    [transform concat];
    [inputImage drawAtPoint:NSMakePoint(0,0)
                         fromRect:NSMakeRect(0,0, dimensions.width, dimensions.height)
                        operation:NSCompositeCopy fraction:1.0];
    [tmpImage unlockFocus];


    return [tmpImage autorelease];

}

用于水平翻转

+ (NSImage *)flipImageHorizontally:(NSImage *)inputImage {

    NSImage *tmpImage;
    NSAffineTransform *transform = [NSAffineTransform transform];

    NSSize dimensions = [inputImage size];
    NSAffineTransformStruct flip = {-1.0, 0.0, 0.0, 1.0,
        dimensions.width, 0.0 };
    tmpImage = [[NSImage alloc] initWithSize:dimensions];
    [tmpImage lockFocus];
    [transform setTransformStruct:flip];
    [transform concat];
    [inputImage drawAtPoint:NSMakePoint(0,0)
                         fromRect:NSMakeRect(0,0, dimensions.width, dimensions.height)
                        operation:NSCompositeCopy fraction:1.0];
    [tmpImage unlockFocus];

    return [tmpImage autorelease];

}

Answer 4

基于the solution of Alejandro Lugeno的Swift扩展：

extension NSImage {
    func flipped(flipHorizontally: Bool = false, flipVertically: Bool = false) -> NSImage {
        let flippedImage = NSImage(size: size)

        flippedImage.lockFocus()

        NSGraphicsContext.current?.imageInterpolation = .high

        let transform = NSAffineTransform()
        transform.translateX(by: flipHorizontally ? size.width : 0, yBy: flipVertically ? size.height : 0)
        transform.scaleX(by: flipHorizontally ? -1 : 1, yBy: flipVertically ? -1 : 1)
        transform.concat()

        draw(at: .zero, from: NSRect(origin: .zero, size: size), operation: .sourceOver, fraction: 1)

        flippedImage.unlockFocus()

        return flippedImage
    }
}