我有一个“地图”，在“itemslayer”处有 100.000 个矩形，
我想要创建动态线条，并将其绘制在前景层。 （也就是说，我不想有很多更新......）
性能很差，你注意到鼠标移动起来很重，我认为这是这条线“接触”的每个矩形的更新。
那么前景层是什么呢？我认为它可以让我在不更新 itemlayer 的情况下绘制 grapchisview ......
也许这与前台没有缓存有关？
有什么想法吗？谢谢。
I have a 'map' with 100.000 rectangles at the 'itemslayer',
I want to have a dynamic line creation and I draw it at Foreground layer. (That is, I dont want to have a lot of updates... )
The performance is poor, you note the mouse heavy to move, An I think that is an update for every rectangle that this line 'touchs' .
What is for the foregroundlayer then? I thought that It'd let me to draw over a grapchisview without updating the itemlayer...
Maybe it is related with there is not cache for foreground ?
Any idea ? Thanks.
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当我阅读 4.8.0 的文档时，它指出：
请注意，QGraphicsView 目前仅支持后台缓存（请参阅 QGraphicsView::CacheBackground）。如果传递了除 QGraphicsScene::BackgroundLayer 之外的任何图层，则此函数相当于调用 update() 。
因此，如果您只想更新前景图层，那么它无论如何都会绘制所有内容，真糟糕...
我知道它是不是答案，但它确实证实了您所看到的。
When I was reading the documentation on 4.8.0 and it states this:
Note that QGraphicsView currently supports background caching only (see QGraphicsView::CacheBackground). This function is equivalent to calling update() if any layer but QGraphicsScene::BackgroundLayer is passed.
So, if you just want to update the foreground layer, then it will draw everything anyways, bummer...
I know it's not a answer, but it does confirm what you are seeing.