使用Swift中的CoreGraphics在屏幕上绘制像素

Question

使用Swift中的CoreGraphics在屏幕上绘制像素

5

下面的代码试图将像素设置为离线位图，并将该位图绘制到屏幕上。不幸的是，它会崩溃。

import UIKit

class GameView: UIView {

    required init?(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)
    }

    override init(frame: CGRect) {
        super.init(frame: frame)
    }


    func createBitmapContext(pixelsWide: Int, _ pixelsHigh: Int) -> CGContextRef? {
        let bytesPerPixel = 4
        let bytesPerRow = bytesPerPixel * pixelsWide
        let bitsPerComponent = 8

        let byteCount = (bytesPerRow * pixelsHigh)

        let colorSpace = CGColorSpaceCreateWithName(kCGColorSpaceGenericRGB)

        let pixels = UnsafeMutablePointer<CUnsignedChar>.alloc(byteCount)
        if pixels == nil {
            return nil
        }
        let bitmapInfo = CGImageAlphaInfo.PremultipliedFirst.rawValue | CGBitmapInfo.ByteOrder32Little.rawValue

        let context = CGBitmapContextCreate(pixels, pixelsWide, pixelsHigh, bitsPerComponent, bytesPerRow, colorSpace, bitmapInfo)

        return context
    }

    override func drawRect(rect: CGRect) {
        let width  = 200
        let height = 300
        let boundingBox = CGRectMake(0, 0, CGFloat(width), CGFloat(height))
        let context = createBitmapContext(width, height)

        let data = CGBitmapContextGetData(context)
        var currentPixel: [UInt32] = unsafeBitCast(data, [UInt32].self)

        var n = 0
        for var j = 0; j < height; j++ {
            for var i = 0; i < width; i++ {
                currentPixel[n++] = 0
            }
        }

        let image = CGBitmapContextCreateImage(context!)
        CGContextDrawImage(context!, boundingBox, image)
    }

}

- John Difool

1个回答

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- Aruna Mudnoor · Accepted Answer

需要进行一些更改。 1. 因为内存溢出而导致崩溃。 2. 你正在从新创建的上下文中创建图像并将其写入相同的上下文，而不是当前的绘图上下文。

请使用这个修改后的drawRect函数：

override func drawRect(rect: CGRect) {
    let width  = 200
    let height = 300
    let boundingBox = CGRectMake(0, 0, CGFloat(width), CGFloat(height))
    let context = createBitmapContext(width, height)

    let data = CGBitmapContextGetData(context)

    let pixels = UnsafeMutablePointer<CUnsignedChar>(data)
    var n = 0
    for var j = 0; j < height; j++ {
        for var i = 0; i < width; i++ {
            pixels[n++] = 0 //B
            pixels[n++] = 255 //G
            pixels[n++] = 0 //R
            pixels[n++] = 255 //A
        }
    }
    let image = CGBitmapContextCreateImage(context!)
    if let currentContext: CGContext! = UIGraphicsGetCurrentContext() {
        UIImagePNGRepresentation(UIImage(CGImage:image!))?.writeToFile("/Users/admin/Desktop/aaaaa.png", atomically: true)
        CGContextDrawImage(currentContext, boundingBox, image)
    }
}