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

Question

I know I can fill a rect using NSRectFill(bounds). However I wanted to preserve transparency for PDF output and I discovered that I can do that only with NSBezierPath(rect: bounds).fill() What is the difference (behind the scenes) of those 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
    }
}

Is it because the compositing mode is NSCompositeCopy? Would NSRectFillUsingOperation have worked better? — matt, Aug 22 '16 at 16:20
Yes, you are completely right. NSRectFillUsingOperation+CompositeCopy does the same as NSRectFill while the NSRectFillUsingOperation+CompositeSourceOver behaves like NSBezierPath + fill. Try to write it as answer and I give you credit. Thanks. — Marek H, Aug 22 '16 at 18:39

score 3 · Accepted Answer · answered Aug 22 '16 at 19:02

I'm mostly an iOS programmer and not very fluent these days over on the AppKit side of things, but my guess is that you're getting the wrong NSCompositingOperation. I see from the docs that NSRectFill uses NSCompositeCopy. Perhaps it would work better if you used NSRectFillUsingOperation, where you get to specify the compositing operation.

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

1 Answers1