addTouch method
Implementation
void addTouch(int pointer, TapDownDetails details) {
this.numberOfTouches++;
if (this.numberOfTouches == 1 && this.onSingleTap != null) {
firstPoint = details.localPosition;
this.onSingleTap!(details.localPosition);
}
if (this.numberOfTouches == 2) {
this.onMultiTap(firstPoint, details.localPosition);
}
}