Poking at Pixels in Swift 4

pixels.swift

import Cocoa

struct Pixel {
    var alpha: UInt8
    var red: UInt8
    var green: UInt8
    var blue: UInt8
    
    init(red: UInt8, green: UInt8, blue: UInt8, alpha: UInt8) {
        self.alpha = alpha
        self.red = red
        self.green = green
        self.blue = blue
    }
    
    static func zero() -> Pixel {
        return self.init(red: 0, green: 0, blue: 0, alpha: 0)
    }
}

do {
    let width: Int = 256
    let height: Int = 256
    
    let count = width*height
    let stride = MemoryLayout<Pixel>.stride
//    let alignment = MemoryLayout<Pixel>.alignment
    let bytesPerRow = stride*width
    let byteCount = bytesPerRow*height
    
    let pointer = UnsafeMutablePointer<Pixel>.allocate(capacity: count)
    pointer.initialize(to: Pixel.zero(), count: count)
    defer {
        pointer.deinitialize(count: count)
        pointer.deallocate(capacity: count)
    }
    
    let buffer = UnsafeMutableBufferPointer(start: pointer, count: count)
    for (i, _) in buffer.enumerated() {
        buffer[i].alpha = 255
        buffer[i].red = 0
        buffer[i].green = 255
        buffer[i].blue = 0
    }
    let data = UnsafeMutableRawPointer(pointer)
    
    let bitmapInfo = CGBitmapInfo(rawValue: CGImageAlphaInfo.premultipliedFirst.rawValue)
    let ctx = CGContext.init(data: data,
                             width: width,
                             height: height,
                             bitsPerComponent: 8,
                             bytesPerRow: bytesPerRow,
                             space: CGColorSpaceCreateDeviceRGB(),
                             bitmapInfo: bitmapInfo.rawValue)
    if let context = ctx {
        let rect = CGRect(origin: CGPoint(x: 0, y: 0), size: CGSize(width: CGFloat(width), height: CGFloat(height))).insetBy(dx: CGFloat(width)/3.0, dy: CGFloat(height)/3.0)
        context.setFillColor(NSColor.red.cgColor)
        context.fill(rect)
        
        let image = context.makeImage()
        let bitmap = NSBitmapImageRep.init(cgImage: image!)
    }
}