Draw NSImage (off-screen)

drawNSImage.m

    NSBitmapImageRep* offscreenRep = [[NSBitmapImageRep alloc]
        initWithBitmapDataPlanes:NULL
                      pixelsWide:size.width
                      pixelsHigh:size.height
                   bitsPerSample:8
                 samplesPerPixel:4
                        hasAlpha:YES
                        isPlanar:NO
                  colorSpaceName:NSCalibratedRGBColorSpace
                     bytesPerRow:0
                    bitsPerPixel:0];

    NSGraphicsContext* nsContext = [NSGraphicsContext graphicsContextWithBitmapImageRep:offscreenRep];
    [NSGraphicsContext saveGraphicsState];
    [NSGraphicsContext setCurrentContext:nsContext];
    
    // Do the drawing using NSGraphics
    
    // Do the drawing using Core Graphics
    CGContextRef cgContext = [nsContext graphicsPort];
    
    NSGraphicsContext restoreGraphicsState];

    NSImage* image = [[NSImage alloc] initWithSize:size];
    [image addRepresentation:offscreenRep];

    return image;