Question

  private void saveInitialMotion(float x, float y, int pointerId) {
    //确保各个数组的大小足够存放数据
    ensureMotionHistorySizeForId(pointerId);
    //保存 x 坐标
    mInitialMotionX[pointerId] = mLastMotionX[pointerId] = x;
    //保存 y 坐标
    mInitialMotionY[pointerId] = mLastMotionY[pointerId] = y;
    //保存是否触摸到边缘
    mInitialEdgesTouched[pointerId] = getEdgesTouched((int) x, (int) y);
    //保存当前 id 是否在触摸，用于后续验证
    mPointersDown |= 1 << pointerId;
  }