Android Canvas ScaleFocus 导致跳跃位置

Question

我正在开发一款游戏，该游戏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。虽然它大部分都在工作，但我有一个奇怪的错误：

在初始缩放之后，如果我再次捏缩放，屏幕跳跃（就像在其他地方滑动并立即移动到那里一样）然后平滑缩放。我已将此行为范围缩小到 scale 函数的 scaleFocus 变量

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

如果我将 scaleFocusX 和 scaleFocusY 设置为 0，则始终使用原点作为缩放焦点，并且不会发生跳跃。但是，当您滚动远离它时，使用原点是不切实际的。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;
}

Answer 1

首先，而不是使用 float[] coordinates = {x, y};你最好使用PointF coordinates = new PointF(x, y);，然后你可以得到x和y与coordinates.x和coordinates.y。

您的问题是在缩放时您仍然处理触摸事件（因此触摸被处理两次）。

我们需要一个全局变量来告诉我们是否正在缩放： boolean scaling = false

所以，在 OnTouchEvent 中你应该检查它：

@Override
    public boolean onTouchEvent(@NonNull MotionEvent event) { 
        detector.onTouchEvent(event);
        if (detector.isInProgress()) 
            scaling = true;

发布： if (event.getAction() == MotionEvent.ACTION_UP) { 缩放=假；

onTouchEvent 中所有与点击一起使用的代码都应该用

包围

if (!scaling) { ... }