如何更快地在 MKMapSnapshotter 上绘图？

Question

我使用以下函数在 MKMapView 的 UIImage 快照上绘制折线。该功能有效，但对我来说太慢了。有没有办法加快速度？

func drawLineOnImageFromLocations(image: UIImage, snapshot: MKMapSnapshot,
                                  polylineLocations: [CLLocation], color: CGColor) -> UIImage {

    UIGraphicsBeginImageContextWithOptions(image.size, true, 0)

    // draw original image into the context
    image.draw(at: CGPoint.zero)

    // get the context for CoreGraphics
    guard let context = UIGraphicsGetCurrentContext() else {
        return image
    }

    context.beginPath()
    context.setLineWidth(10)
    context.setStrokeColor(color)
    let coordinates = polylineLocations.map{[=10=].coordinate}
    var points = [CGPoint]()
    for coordinate in coordinates {
        let point = snapshot.point(for: coordinate)
        points.append(point)
    }
    context.addLines(between: points)
    context.strokePath()

    // get the image from the graphics context
    let resultImage = UIGraphicsGetImageFromCurrentImageContext()
    // end the graphics context
    UIGraphicsEndImageContext()

    return resultImage!
}

Answer 1

结果调用：

UIGraphicsBeginImageContextWithOptions(image.size, true, 0)

是一个非常昂贵的操作。如果您可以重构您的代码以仅调用一次，它将大大加快速度。