How to convert COpaquePointer in swift to some type (CGContext? in particular)

Question

I have the following code in swift which doesn't compile:

class CustomView: NSView {
  override func drawRect(dirtyRect: NSRect) {
    var contextPointer: COpaquePointer = NSGraphicsContext.currentContext()!.graphicsPort()
    var context: CGContext? = contextPointer as? CGContext
    CGContextSetRGBFillColor(context, 1, 0, 0, 1)
    CGContextFillRect(context, CGRectMake(0, 0, 100, 100))
    CGContextFlush(context)
  }
}

How do I convert COpaquePointer to CGContext?

score 10 · Answer 1 · answered Aug 07 '14 at 20:26

10

As of Developer Preview 5, NSGraphicsContext now has a CGContext property. It's not documented yet but it's in the header file:

@property (readonly) CGContextRef CGContext NS_RETURNS_INNER_POINTER NS_AVAILABLE_MAC(10_10);

answered Aug 07 '14 at 20:26

robotspacer

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50

score 7 · Answer 2 · answered Jun 04 '14 at 15:41

7

This is kind of ugly; it would be better if the graphicsPort() method was updated to return a CGContextRef directly (like UIGraphicsGetCurrentContext()), rather than a void*. I added this extension to NSGraphicsContext to sweep it under the rug for now:

extension NSGraphicsContext {
  var cgcontext: CGContext {
    return Unmanaged<CGContext>.fromOpaque(self.graphicsPort()).takeUnretainedValue()
  }
}

Just call NSGraphicsContext.currentContext().cgcontext anywhere you need a CGContext.

answered Jun 04 '14 at 15:41

jatoben

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I wasn't aware of `Unmanaged`, or `fromOpaque`, but this works beautifully! Thanks! – alaroldai Jul 07 '14 at 06:26
1

However, using the `reinterpretCast` sledgehammer seems to work – alaroldai Jul 08 '14 at 07:44
What `reinterpretCast`? I typed that into Xcode doc search and got nothing. The new line code would help. – Rob N Jul 14 '14 at 15:14
This works: `return reinterpretCast(self.graphicsPort())`; and here's an [example gist](https://gist.github.com/anonymous/6d1b7ed422debb26b543) – FluffulousChimp Jul 16 '14 at 02:24

score 3 · Answer 3 · answered Jun 03 '14 at 08:06

3

This seems to be compiling:

var contextPointer = NSGraphicsContext.currentContext()!.graphicsPort()
let context = UnsafePointer<CGContext>(contextPointer).memory

answered Jun 03 '14 at 08:06

Alfa07

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Thanks! Not sure you need to use .currentContext()! though - isn't the type of currentContext already unwrapped? `class func currentContext() -> NSGraphicsContext!` – alaroldai Jun 03 '14 at 09:18
@alaroldai Yes, but I need CGContext not NSGraphicsContext – Alfa07 Jun 03 '14 at 18:21
See http://stackoverflow.com/questions/24016668/how-to-use-implicitly-unwrapped-optionals/24056236#24056236 – klotz Sep 24 '14 at 15:18

score 1 · Answer 4 · answered Jul 01 '14 at 11:52

You are almost near. Try this code

class CustomView: NSView {
    override func drawRect(dirtyRect: NSRect) {

        var contextPointer = NSGraphicsContext.currentContext()!.graphicsPort()
        var context = UnsafePointer<CGContext>(contextPointer).memory

        CGContextSetRGBFillColor(context, 1.0, 0.0, 0.0, 1.0)
        CGContextFillRect(context, CGRectMake(0, 0, 100, 100))
        CGContextFlush(context)
    }
}

eonil · Answer 5 · 2016-04-15T21:34:16.040

In Xcode 6.3 / Swift 1.2, NSGraphicsContext.currentContext()!.graphicsPort returns UnsafeMutablePointer<Void> and you can cast it into CGContextRef using unsafeBitCast because it's just a C pointer. This just reinterpret the pointer value, so should work exactly same with C forced point cast.

    let p1  =   NSGraphicsContext.currentContext()!.graphicsPort
    let ctx =   unsafeBitCast(p1, CGContextRef.self)

Please take care that such reinterpreting-cast is always very dangerous and used only when you're sure on what you're doing.

How to convert COpaquePointer in swift to some type (CGContext? in particular)

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