ios - 值类型和 init 的问题

Question

我正在关注 old tutorial关于设置数据结构以查看图像中的 RGBA 值。在大多数情况下，我已经克服了所有数据不足的问题，但我遇到了一个看起来非常简单的问题，我只是对 swift 比较陌生，所以事实证明它有点困难。

import UIKit

public struct RGBAPixel {
    public init(rawVal : UInt32) {
        raw = rawVal
    }
    public var raw: UInt32
    public var red: UInt8 {
        get { return UInt8(raw & 0xFF) }
        set { raw = UInt32(newValue) | (raw & 0xFFFFFF00) }
    }
    public var green: UInt8 {
        get { return UInt8( (raw & 0xFF00) >> 8) }
        set { raw = (UInt32(newValue) << 8) | (raw & 0xFFFF00FF) }
    }
    public var blue: UInt8 {
        get { return UInt8( (raw & 0xFF0000) >> 16) }
        set { raw = (UInt32(newValue) << 16) | (raw & 0xFF00FFFF) }
    }
    public var alpha: UInt8 {
        get { return UInt8( (raw & 0xFF000000) >> 24) }
        set { raw = (UInt32(newValue) << 24) | (raw & 0x00FFFFFF) }
    }
}

let image = UIImage(named: "crossSection.jpg")

let height = Int((image?.size.height)!)
let width = Int((image?.size.width)!)
let bitsPerComponent = Int(8)
let bytesPerRow = 4 * width
let colorSpace = CGColorSpaceCreateDeviceRGB()
let rawData = UnsafeMutablePointer<UInt32>.allocate(capacity: width * height)
let bitmapInfo: UInt32 = CGBitmapInfo.byteOrder32Big.rawValue | CGImageAlphaInfo.premultipliedLast.rawValue
let CGPointZero = CGPoint(x: 0,y: 0)
let rect = CGRect(origin: CGPointZero, size: (image?.size)!)

let imageContext = CGContext(data: rawData, width: width, height: height, bitsPerComponent: bitsPerComponent, bytesPerRow: bytesPerRow, space: colorSpace, bitmapInfo: bitmapInfo)

imageContext?.draw(image!.cgImage!, in:rect)

let pixels = UnsafeMutableBufferPointer<UInt32>(start: rawData, count: width * height)

///*
for var y in 0 ..< height {
    for var x in 0 ..< width {
        var p = pixels[x+y*width] = RGBAPixel(rawVal: 0)
        p.red = 255
        pixels[x+y*width] = p


    }
}
//*/

let outContext = CGContext(data: pixels.baseAddress, width: width, height: height, bitsPerComponent: bitsPerComponent, bytesPerRow: bytesPerRow, space: colorSpace, bitmapInfo: bitmapInfo)

let outImage = UIImage(cgImage: outContext!.makeImage()!)

有两个问题点。首先是底部附近的问题，当放入 swift 时它会给出错误“无法将类型‘RGBAPixel’的值分配给类型‘UInt32’”。我关注了video很好，并寻找我似乎找不到的任何错误。这个问题似乎不是更新引起的，所以我很困惑。我研究了结构和初始化，代码的编写方式似乎很有意义。 init 允许通过 RGBAPIxel 传入数据类型 UInt32。同样，非常新，所以请纠正我哪里我错了。谢谢

Answer 1

您正在使用 <UInt32>而不是 <RGBAPixel>

let rawData = UnsafeMutablePointer<UInt32>.allocate(capacity: width * height)
//Should be:
let rawData = UnsafeMutablePointer<RGBAPixel>.allocate(capacity: width * height)

同理:

let pixels = UnsafeMutableBufferPointer<UInt32>(start: rawData, count: width * height)
// Should be:
let pixels = UnsafeMutableBufferPointer<RGBAPixel>(start: rawData, count: width * height)

试试这个(为了便于阅读，我添加了一些空行)- 使用黑色作为颜色:

import UIKit

struct RGBAPixel {
    var raw: UInt32

    public init(rawVal : UInt32) {
        raw = rawVal
    }

    public var red: UInt8 {
        get { return UInt8(raw & 0xFF) }
        set { raw = UInt32(newValue) | (raw & 0xFFFFFF00) }
    }

    public var green: UInt8 {
        get { return UInt8( (raw & 0xFF00) >> 8) }
        set { raw = (UInt32(newValue) << 8) | (raw & 0xFFFF00FF) }
    }

    public var blue: UInt8 {
        get { return UInt8( (raw & 0xFF0000) >> 16) }
        set { raw = (UInt32(newValue) << 16) | (raw & 0xFF00FFFF) }
    }

    public var alpha: UInt8 {
        get { return UInt8( (raw & 0xFF000000) >> 24) }
        set { raw = (UInt32(newValue) << 24) | (raw & 0x00FFFFFF) }
    }
}

let image = UIImage(named: "crossSection.jpg")

let height = Int((image?.size.height)!)
let width = Int((image?.size.width)!)

let bitsPerComponent = Int(8)
let bytesPerRow = 4 * width

let colorSpace = CGColorSpaceCreateDeviceRGB()

let rawData = UnsafeMutablePointer<RGBAPixel>.allocate(capacity: width * height)

let bitmapInfo: UInt32 = CGBitmapInfo.byteOrder32Big.rawValue | CGImageAlphaInfo.premultipliedLast.rawValue

let CGPointZero = CGPoint(x: 0,y: 0)

let rect = CGRect(origin: CGPointZero, size: (image?.size)!)

let imageContext = CGContext(data: rawData, width: width, height: height, bitsPerComponent: bitsPerComponent, bytesPerRow: bytesPerRow, space: colorSpace, bitmapInfo: bitmapInfo)

imageContext?.draw(image!.cgImage!, in:rect)

let pixels = UnsafeMutableBufferPointer<RGBAPixel>(start: rawData, count: width * height)

///*
for var y in 0 ..< height {
    for var x in 0 ..< width {
        pixels[x+y*width] = RGBAPixel(rawVal: 0xFF000000)
    }
}
//*/

let outContext = CGContext(data: pixels.baseAddress, width: width, height: height, bitsPerComponent: bitsPerComponent, bytesPerRow: bytesPerRow, space: colorSpace, bitmapInfo: bitmapInfo)

let outImage = UIImage(cgImage: outContext!.makeImage()!)

使用颜色:

for var y in 0 ..< height {
    for var x in 0 ..< width {
        var p = RGBAPixel(rawVal: 0xFF000000)
        p.red = 128
        pixels[x+y*width] = p
    }
}