CGContextDrawImage与Swift

Question

有时，CGContextDrawImage会导致“错误访问错误”，执行下面的代码，我们无法找到原因。是否有人在使用"CGContextDrawImage“时遇到过同样的错误？

    let bytesPerPixel = 4;
    let bytesPerRow:UInt = UInt(bytesPerPixel) * UInt(CG_Width)
    let bitsPerComponent:UInt = 8;

    let bitmapInfo = CGBitmapInfo(CGImageAlphaInfo.PremultipliedLast.rawValue)

    var pixel = UnsafeMutablePointer<CUnsignedChar>.alloc(4)



    let context = CGBitmapContextCreate(pixel,
        UInt(CG_Width), UInt(CG_Width), bitsPerComponent, bytesPerRow, colorSpace, bitmapInfo)



    let cgRect:CGRect = CGRectMake (0,0,CGFloat(CG_Width),CGFloat(CG_Width)) as CGRect



    CGContextDrawImage(context, cgRect, imageRef) 

Answer 1

当您创建像素缓冲区时，您只分配了4个字节，这对于1x1位图来说就足够了。想必，CG_Width ( CG_Height在哪里使用？)不是1，所以当你欺骗CGBitmapContextCreate关于缓冲区的大小，然后进入它时，你在随机内存中乱写。将缓冲区分配更改为：

var pixel = UnsafeMutablePointer<CUnsignedChar>.alloc(bytesPerRow * CG_Height)

然后将上下文创建更改为使用正确的高度：

let context = CGBitmapContextCreate(pixel,
    UInt(CG_Width), UInt(CG_Height), bitsPerComponent, bytesPerRow, colorSpace, bitmapInfo)

如果您实际上是有意创建一个方形位图，请将我的CG_Height更改为CG_Width