What is the difference between NSRectFill and NSBezierPath (rect) .fill

Question

I know that I can fill a rectangle using NSRectFill (bounds). However, I wanted to maintain transparency for PDF output, and I found that I can only do this with NSBezierPath (rect: bounds) .fill () What is the difference (behind the scenes) of the two?

func drawBackground() {
    CGContextSaveGState(currentContext)
    if (NSGraphicsContext.currentContextDrawingToScreen()) {
        NSColor(patternImage: checkerboardImage).set()
        NSRectFillUsingOperation(bounds, NSCompositingOperation.CompositeSourceOver)
    }
    NSColor.clearColor().setFill()
    //NSRectFill(bounds) //option 1
    NSBezierPath(rect: bounds).fill() // option 2
    CGContextRestoreGState(currentContext)
}

extension NSImage {

    static func checkerboardImageWithSize(size : CGFloat) -> NSImage {
        let fullRect = NSRect(x: 0, y: 0, width: size, height: size)
        let halfSize : CGFloat = size * 0.5;
        let upperSquareRect = NSRect(x: 0, y: 0, width: halfSize, height: halfSize);
        let bottomSquareRect = NSRect(x: halfSize, y: halfSize, width:halfSize, height: halfSize);
        let image = NSImage(size: NSSize(width: size, height: size))
        image.lockFocus()
        NSColor.whiteColor()
        NSRectFill(fullRect)
        NSColor(deviceWhite: 0.0, alpha:0.1).set()
        NSRectFill(upperSquareRect)
        NSRectFill(bottomSquareRect)
        image.unlockFocus()
        return image
    }
}

Answer 1

, , iOS AppKit, , NSCompositingOperation. , NSRectFill NSCompositeCopy. , , NSRectFillUsingOperation, .