在Swift中将CFContextRef转换为可变的void指针？

Question

I'm trying to convert this objc code to swift:

CGContextRef contextRef = CGBitmapContextCreate(NULL,
                                                proposedRect.size.width,
                                                proposedRect.size.height,
                                                CGImageGetBitsPerComponent(imageRef),
                                                0,
                                                colorSpaceRef,
                                                (CGBitmapInfo)kCGImageAlphaPremultipliedFirst);
NSGraphicsContext *context = [NSGraphicsContext graphicsContextWithGraphicsPort:contextRef flipped:NO];

So far I ended up with this:

var bitmapContext: CGContext = CGBitmapContextCreate(data, UInt(proposedRect.width), UInt(proposedRect.height), CGImageGetBitsPerComponent(image), 0, colorSpace, CGBitmapInfo(CGImageAlphaInfo.PremultipliedFirst.toRaw()))
let context = NSGraphicsContext(graphicsPort: bitmapContext, flipped: false)

The problem is that CGBitmapContextCreate returns CGContext type and NSGraphicsContext initializer accepts graphicsPort as CMutableVoidPointer type. So how can I convert CGContext to CMutableVoidPointer ?

related reverse type casting found here, but it didn't provide much help to me How to convert COpaquePointer in swift to some type (CGContext? in particular)

Answer 1

I ended up with the reinterpretCast function returning intermediate Int variable for the bitmapContext address.

var bitmapContext: CGContext = CGBitmapContextCreate(...)

let bitmapContextAddress: Int = reinterpretCast(bitmapContext)
let bitmapContextPointer: CMutableVoidPointer = COpaquePointer(UnsafePointer<CGContext>(bitmapContextAddress))
let context = NSGraphicsContext(graphicsPort: bitmapContextPointer, flipped: false)

Answer 2

The documentation here: https://developer.apple.com/library/prerelease/ios/documentation/swift/conceptual/buildingcocoaapps/InteractingWithCAPIs.html

states the following:

When a function is declared as taking a CMutableVoidPointer argument, it can accept the same operands as CMutablePointer for any type Type.

From that, it should work like this:

var p: CMutablePointer<CGContext> = &bitmapContext
NSGraphicsContext *context = [NSGraphicsContext graphicsContextWithGraphicsPort:p flipped:NO];

Extended practically, you should be able to pass in &bitmapContext directly to a CMutableVoidPointer argument.

Swift doesn't have "pointers" in the C sense.