android - 如何让路线绘制更高效？

Question

这是我用来绘制路线的代码。当我有 1000 个点时，路线会严重减慢用户界面。也许有人可以提供代码 fragment 或链接来解释如何更有效地绘制路线？我知道解决这个问题的一种方法是缓存位图路径，但不知道该怎么做。

public class PathOverlay extends Overlay{

private GeoPoint startPoint;
private GeoPoint finishPoint;
private ArrayList<GeoPoint> pathPoints;
private Paint paint;
private Path path;
private Point pathStartPoint;
private Point pathEndPoint;

private float dx;
private float dy;


public PathOverlay(GeoPoint startPoint, GeoPoint finishPoint, ArrayList<GeoPoint> pathPoints, int color){
    this.startPoint = startPoint;
    this.finishPoint = finishPoint;
    this.pathPoints = pathPoints;
    this.paint = new Paint();
    this.paint.setAntiAlias(true);
    this.paint.setDither(true);
    this.paint.setColor(color);
    this.paint.setAlpha(150);
    this.paint.setStrokeWidth(4);
    this.paint.setStyle(Paint.Style.STROKE);
}

@Override
public void draw(Canvas overlayCanvas, MapView mapView, boolean shadow) {
    if(path == null) {
        path = getPath(mapView);
    } else {
        path = transformPath(mapView);
    }
    overlayCanvas.drawPath(path, paint);
    super.draw(overlayCanvas, mapView, shadow);
}

private Path getPath(MapView mapView) {
    Projection projection = mapView.getProjection();
    if(path == null) {
        path = new Path();
        path.setFillType(FillType.WINDING);
    } else {
        path.rewind();
    }
    Point point = new Point();
    pathStartPoint = new Point();
    pathEndPoint = new Point();

    projection.toPixels(startPoint, point);
    projection.toPixels(startPoint, pathStartPoint);
    path.moveTo(point.x, point.y);
    path.addCircle(point.x, point.y, (float) 2.0, Direction.CCW);
    if (pathPoints != null) {
        for(int i=0;i<pathPoints.size();i++) {
            projection.toPixels(pathPoints.get(i), point);
            path.lineTo(point.x, point.y);
        }
    }
    projection.toPixels(finishPoint, point);
    projection.toPixels(finishPoint, pathEndPoint);
    path.lineTo(point.x-5, point.y);
    path.addCircle(point.x-5, point.y, (float) 2.0, Direction.CCW);


    return path;
}

private Path transformPath(MapView mapView) {
    Projection projection = mapView.getProjection();

    Point sPoint = new Point();
    Point ePoint = new Point();
    projection.toPixels(startPoint, sPoint);
    projection.toPixels(finishPoint, ePoint);

    float sx = ((float)ePoint.x - (float)sPoint.x)/((float)pathEndPoint.x - (float)pathStartPoint.x);
    float sy = ((float)ePoint.y - (float)sPoint.y)/((float)pathEndPoint.y - (float)pathStartPoint.y);

    if(sx != 1.0 && sy != 1.0) {
        Log.i("PathOverlay", "resized");
        return getPath(mapView);
    } else {
        Log.i("PathOverlay", "moved");
        Matrix matrix = new Matrix();

        dx = (float)sPoint.x - (float)pathStartPoint.x;
        dy = (float)sPoint.y - (float)pathStartPoint.y;

        matrix.postTranslate(dx, dy);
        pathStartPoint = sPoint;
        pathEndPoint = ePoint;
        path.transform(matrix);

        return path;
    }
}

}

Answer 1

您可以绘制通向透明 Bitmap 对象的路径(无论您认为合适的大小 - 它越大，路径的细节越好，但内存消耗越高)。

确保使用 Bitmap.config.ARGB_8888 创建它以实现透明度。

完成此操作后，您将使用两个矩形在 Overlay 上显示路径:

• 确定路径的哪一部分可见的源矩形
• 一个目标矩形，用于确定您要在 Overlay Canvas 上的哪个位置显示这条路径。

您将使用 Canvas.drawBitmap(Bitmap bitmap, Rect src, RectF dst, Paint paint)

应该不会太难，您已经在 transformPath 方法中完成了大部分重要的计算。

添加:

实际上，您可以结合使用绘制到位图的路径和重绘实际路径点。当用户在 map 上移动或放大/缩小时使用上述技术，然后在用户松开屏幕时重新绘制路径。