将SKSpriteNode缩放到点的方向（夹点）

Question

我有一个Spritekit游戏和一个SKSpriteNode（mapContainer），它是地图，而该地图位于另一个SKSpriteNode（rightCon）中，它是它的容器。当挤入/缩小时我想在地图上放大/缩小。

我已经在网上找到了代码并设法获得了似乎有用的东西，但这不太对。

问题在于，一旦我开始捏它就跳了一点（我的意思是，地图明显地移动位置而不是平稳地移动），然后它平滑地放大/缩小到捏。而且我不确定为什么。

- (void)rightConPTZ:(UIPinchGestureRecognizer *)recognizer {

    CGPoint touchLocation = [recognizer locationInView:recognizer.view];
    touchLocation = [self convertPointFromView:touchLocation];

    CGPoint pointInMap = [rightCon convertPoint:touchLocation fromNode:self];

    if (recognizer.state == UIGestureRecognizerStateChanged) {
        float scale = recognizer.scale-lastScale;

        mapContainer.xScale += scale;
        mapContainer.yScale += scale;

        float centerX = 0;
        float centerY = 0;

        float offsetToCenterX = centerX-pointInMap.x;
        float offsetToCenterY = centerY-pointInMap.y;

        float multiX = offsetToCenterX*mapContainer.xScale;
        float multiY = offsetToCenterY*mapContainer.xScale; //xscale & yscale are the same (and always will be)

        float zoomInFactor = 2;

        float scaleDiff = (zoomInFactor - mapContainer.xScale) / (zoomInFactor - 1.0f);

        float multiX2 = offsetToCenterX*scaleDiff;
        float multiY2 = offsetToCenterY*scaleDiff;

        float subX = multiX-multiX2;
        float subY = multiY-multiY2;

        mapContainer.position = CGPointMake(subX, subY);

        lastScale = recognizer.scale;
    } else if (recognizer.state == UIGestureRecognizerStateEnded) {
        lastScale = 1.0;
    }
}

任何人都可以看到问题可能是什么？在代码中是否存在错误，或者我（我怀疑）是否在这个等式中留下了一些重要的部分，以便平滑地缩放到夹点？