rotate a NSImage

NSImage+Rotated.h

#import <Cocoa/Cocoa.h>

@interface NSImage (Rotated)
- (NSImage *)imageRotated:(float)degrees;
- (CGImageRef)toCGImageRef;
@end

NSImage+Rotated.m

#import "NSImage+Rotated.h"

@implementation NSImage (Rotated)

- (NSImage *)imageRotated:(float)degrees {

    degrees = fmod(degrees, 360.);
    if (0 == degrees) {
        return self;
    }
    NSSize size = [self size];
    NSSize maxSize;
    if (90. == degrees || 270. == degrees || -90. == degrees || -270. == degrees) {
        maxSize = NSMakeSize(size.height, size.width);
    } else if (180. == degrees || -180. == degrees) {
        maxSize = size;
    } else {
        maxSize = NSMakeSize(20+MAX(size.width, size.height), 20+MAX(size.width, size.height));
    }
    NSAffineTransform *rot = [NSAffineTransform transform];
    [rot rotateByDegrees:degrees];
    NSAffineTransform *center = [NSAffineTransform transform];
    [center translateXBy:maxSize.width / 2. yBy:maxSize.height / 2.];
    [rot appendTransform:center];
    NSImage *image = [[NSImage alloc] initWithSize:maxSize];
    [image lockFocus];
    [rot concat];
    NSRect rect = NSMakeRect(0, 0, size.width, size.height);
    NSPoint corner = NSMakePoint(-size.width / 2., -size.height / 2.);
    [self drawAtPoint:corner fromRect:rect operation:NSCompositeCopy fraction:1.0];
    [image unlockFocus];
    return image;
}

- (CGImageRef)toCGImageRef
{
//    NSData *imageData = [self TIFFRepresentation];
    
    NSBitmapImageRep *bmprep = [self bitmapImageRepresentation];

    NSData *imageData = [bmprep representationUsingType:NSPNGFileType properties:@{NSImageCompressionFactor: @(0.0)}];
    
    
    CGImageRef imageRef = NULL;
    if (imageData) {
        CGImageSourceRef imageSource = CGImageSourceCreateWithData((CFDataRef)imageData, NULL);
        imageRef = CGImageSourceCreateImageAtIndex(imageSource, 0, NULL);
    }
    return imageRef;
}

- (NSBitmapImageRep *)bitmapImageRepresentation {
    int width = [self size].width;
    int height = [self size].height;
    
    if(width < 1 || height < 1)
        return nil;
    
    NSBitmapImageRep *rep = [[NSBitmapImageRep alloc]
                             initWithBitmapDataPlanes: NULL
                             pixelsWide: width
                             pixelsHigh: height
                             bitsPerSample: 8
                             samplesPerPixel: 4
                             hasAlpha: YES
                             isPlanar: NO
                             colorSpaceName: NSDeviceRGBColorSpace
                             bytesPerRow: width * 4
                             bitsPerPixel: 32];
    
    NSGraphicsContext *ctx = [NSGraphicsContext graphicsContextWithBitmapImageRep: rep];
    [NSGraphicsContext saveGraphicsState];
    [NSGraphicsContext setCurrentContext: ctx];
    [self drawAtPoint: NSZeroPoint fromRect: NSZeroRect operation: NSCompositeCopy fraction: 1.0];
    [ctx flushGraphics];
    [NSGraphicsContext restoreGraphicsState];
    
    return [rep autorelease];
}

@end