Android Canvas ScaleFocus导致跳跃位置

我正在做一个游戏,它将俯视一个移动棋子的网格(类似于国际象棋)。我希望用户能够平移和缩放地图。我一直在对矩阵进行转换,然后将这些更改连接到画布矩阵。虽然它大部分时间都在工作,但我有一个奇怪的错误:

初始缩放后,如果我再次缩小缩放,屏幕 跳跃 (这就像是在别的地方滑动,它立刻移动到那里),然后平滑地缩放。我已经将这种行为缩小到scale函数的scaleFocus变量

canvas.scale(scaleFactor, scaleFactor, scaleFocusX, scaleFocusY);

如果我将scaleFocusX和scaleFoFocusY设置为0,则始终使用原点作为缩放焦点,不会发生跳跃。但是,使用原点并不实用,因为您滚动到离原点更远的位置。这是我的代码摘要。

public void onDraw(Canvas canvas) {
  ...
  canvas.translate(-mPosX, -mPosY);
  canvas.scale(scaleFactor, scaleFactor, scaleFocusX, scaleFocusY);

  //Create an inverse of the tranformation matrix, to be used when determining click location.
  canvas.getMatrix().invert(canvasMatrix);
  ... }


public class MyOnScaleGestureListener extends
        ScaleGestureDetector.SimpleOnScaleGestureListener {

    @Override
    public boolean onScale(ScaleGestureDetector detector) {

        scaleFactor *= detector.getScaleFactor();
        // Don't let the object get too small or too large.
        scaleFactor = Math.max(MIN_SCALE, Math.min(scaleFactor, MAX_SCALE));
        return true;
    }

    @Override
    public boolean onScaleBegin(ScaleGestureDetector detector) {
        Point scaleFocus = calculateClickAbsoluteLocation
                (detector.getFocusX(), detector.getFocusY());
        scaleFocusX = scaleFocus.x;
        scaleFocusY = scaleFocus.y;
        return true;
    }

    @Override
    public void onScaleEnd(ScaleGestureDetector detector) {

    }


//This method will take point on the phone screen, and convert it to be
//a point on the canvas (since the canvas area is larger than the screen).
public Point calculateClickAbsoluteLocation(float x, float y) {
    Point result = new Point();
    float[] coordinates = {x, y};

    //MapPoints will essentially convert the click coordinates from "screen pixels" into
    //"canvas pixels", so you can determine what tile was clicked.
    canvasMatrix.mapPoints(coordinates);

    result.set((int)coordinates[0], (int)coordinates[1]);
    return result;
}