I found some potential issues in the caching in GraphicsItem.pixelVectors.

In both the local cache lookup:

and global cache lookup:

the cached value is used if direction is None (implicitly QtCore.QPointF(1, 0)). However, the cached value may have been calculated for any direction, and the direction does seem not affect the key obtained from dt. This may result in returning an incorrect value in when pixelVectors has been called with an explicit direction prior to calling it with direction=None.

Furthermore, when pixelVectors is called with direction=Point([1, 0]), as done here:

and here

through here:

No cache lookup is done since direction is not None, but should be since it's set to that value implicitly if direction is None. This slows down updating e.g. InfiniteLines a lot, which is an issue for a project I'm currently working on.

I'd be happy to help out fixing this, but I'd like to know what the intended behavior is first. Is including the direction in the cache key and then not checking if direction is None a potential good fix/improvement?