I have found an example of Objective-C code that gets the color of a pixel at a point here: How to get the pixel color on touch?
The specific section of code I need help with is where the context is created using CGColorSpaceCreateDeviceRGB:
---This is the Objective-C code
unsigned char pixel[4] = {0};
CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
CGContextRef context = CGBitmapContextCreate(pixel,
1, 1, 8, 4, colorSpace, (CGBitmapInfo)kCGImageAlphaPremultipliedLast);
CGContextTranslateCTM(context, -point.x, -point.y);
My best attempt looks as follows (I'm not returning anything yet I'm trying to get the context properly first):
---This is my best attempt at a Swift conversion
func getPixelColorAtPoint()
{
let pixel = UnsafeMutablePointer<CUnsignedChar>.alloc(1)
var colorSpace:CGColorSpaceRef = CGColorSpaceCreateDeviceRGB()
let context = CGBitmapContextCreate(pixel, width: 1, height: 1, bitsPerComponent: 8, bytesPerRow: 4, space: nil, bitmapInfo: CGImageAlphaInfo.PremultipliedLast)
}
However this gives me an error
Cannot convert the expression's type '(UnsafeMutablePointer<CUnsignedChar>, width: IntegerLiteralConvertible, height: IntegerLiteralConvertible, bitsPerComponent: IntegerLiteralConvertible, bytesPerRow: IntegerLiteralConvertible, space: NilLiteralConvertible, bitmapInfo: CGImageAlphaInfo)' to type 'IntegerLiteralConvertible'
If you could advise how I need to tweak my code above to get the context function paramters entered correctly I would appreciate it thank you!
There are two different problems:
CGBitmapContextCreate()
is a function, not a method, and therefore does not
use external parameter names by default.CGImageAlphaInfo.PremultipliedLast
cannot be passed as bitmapInfo:
parameter,
compare Swift OpenGL unresolved identifier kCGImageAlphaPremultipliedLast.So this should compile:
let pixel = UnsafeMutablePointer<CUnsignedChar>.alloc(4)
var colorSpace = CGColorSpaceCreateDeviceRGB()
let bitmapInfo = CGBitmapInfo(CGImageAlphaInfo.PremultipliedLast.rawValue)
let context = CGBitmapContextCreate(pixel, 1, 1, 8, 4, colorSpace, bitmapInfo)
// ...
pixel.dealloc(4)
Note that you should allocate space for 4 bytes, not 1.
Alternatively:
var pixel : [UInt8] = [0, 0, 0, 0]
var colorSpace = CGColorSpaceCreateDeviceRGB()
let bitmapInfo = CGBitmapInfo(CGImageAlphaInfo.PremultipliedLast.rawValue)
let context = CGBitmapContextCreate(UnsafeMutablePointer(pixel), 1, 1, 8, 4, colorSpace, bitmapInfo)