vImage_Buffer Unsafe Mutable Pointers

gistfile1.txt

let srcRowBytes = workingBuffer.buffer.rowBytes

let srcData: UnsafeMutablePointer<Pixel_8> = workingBuffer.buffer.data!.assumingMemoryBound(to: Pixel_8.self)
let srcIndex = y * srcRowBytes + x * workingBuffer.bytesPerPixel

var srcPointer = srcData[srcIndex]
withUnsafeMutablePointer(to: &srcPointer) { srcPointer in
	// srcPointer is (UnsafeMutablePointer<Pixel_8>)
	var srcBuffer = vImage_Buffer(data: srcPointer, height: vImagePixelCount(h), width: vImagePixelCount(w), rowBytes: srcRowBytes)

	...

	var error = kvImageNoError
    	// EXC_BAD_ACCESS because srcPointer is not srcData + srcIndex
	error = vImageConvert_AnyToAny(converter, &srcBuffer, &dstBuffer, nil, vImage_Flags(kvImagePrintDiagnosticsToConsole))
}

Previously, this code was:

var srcBuffer = vImage_Buffer(data: &srcData[srcIndex], height: vImagePixelCount(h), width: vImagePixelCount(w), rowBytes: srcRowBytes)

But there's an inout warning about the &srcData temporary pointer:

Inout expression creates a temporary pointer, but argument 'data' should be a pointer that outlives the call to 'init(data:height:width:rowBytes:)'

For anyone who stumbles across this gist with search, the fix is to create the vImage_Buffer like this:

var srcBuffer = vImage_Buffer(data: srcData.advanced(by: srcIndex), height: vImagePixelCount(h), width: vImagePixelCount(w), rowBytes: srcRowBytes)

For more help, check out these links:

Apple documentation: https://developer.apple.com/documentation/accelerate/applying_vimage_operations_to_regions_of_interest
Twitter thread: https://twitter.com/chockenberry/status/1450885687369101313