Accelerate.vImage 之 ROI: 剪切图片

vImage_ROI

• Crop image with ROI(BGRA8888)

  • Core implementation

    • Validate roi

    • Calculate pixels in roi

    • Fill pixels in desBuffer

      typealias vImageBuffer = UnsafeMutablePointer
      
      @discardableResult
      func vImageBuffer_CropRGBA8888(_ src: vImageBuffer, _ des: vImageBuffer, _ roi: CGRect) -> vImage_Error {
      
          let bufferWidth = Int(src.pointee.width)
          let bufferHeight = Int(src.pointee.height)
      
          /// validate roi
          let roi = roi.intersection(CGRect(x: 0, y: 0, width: bufferWidth, height: bufferHeight))
      
          /// calculate pixels in roi
          /// start: ths first pixel at the topleft in roi
          let bytesPerPixel = 4
          let start = Int(roi.minY) * src.pointee.rowBytes + Int(roi.minX) * bytesPerPixel
      
          /// fill pixels in desBuffer
          /// WARNING: the image data shared between srcBuffer and desBuffer, NOT COPY
          /// so we should call `free(srcBuffer.data) only`
          defer {
              des.pointee.rowBytes = src.pointee.rowBytes
              des.pointee.data = src.pointee.data.advanced(by: start)
          }
      
          return vImageBuffer_Init(des,
                            .init(roi.height),
                            .init(roi.width),
                            32,
                            .init(kvImageNoFlags))
      
      }
      
      

  • Create srcBuffer/desBuffer

    let sourceImage = #imageLiteral(resourceName: "Food_4").cgImage(forProposedRect: nil, context: .current, hints: nil)!
    
    guard var sourceBuffer = try? vImage_Buffer(cgImage: sourceImage) else {
        return
    }
    
    var destinationBuffer = vImage_Buffer()
    
    

  • Call crop

    vImageBuffer_CropRGBA8888(
        &sourceBuffer,
        &destinationBuffer,
        CGRect(x: 100, y: 100, width: 3000, height: 400))
    
    

  • Display/Validate

    let format = vImage_CGImageFormat(bitsPerComponent: .init(sourceImage.bitsPerComponent),
                                      bitsPerPixel: .init(sourceImage.bitsPerPixel),
                                      colorSpace: .passUnretained(sourceImage.colorSpace!),
                                      bitmapInfo: sourceImage.bitmapInfo,
                                      version: 0,
                                      decode: sourceImage.decode,
                                      renderingIntent: sourceImage.renderingIntent)
    
    guard let finalImage = try? destinationBuffer.createCGImage(format: format) else {
        return
    }
    
    imageView.image =  NSImage(cgImage: finalImage,
                               size: CGSize(width: finalImage.width, height: finalImage.height))
    
    

  • free memory

    defer {
        sourceBuffer.free()
        /// DO NOT CALL 
        /// destinationBuffer.free()
    }