Pixel buffer cacheing sometimes doesn't work with overlayed curves?

[goodboy]

Been noticing that sometimes when you have a curve overlayed with the primary OHLC graphics that .paint() is being triggered more then you'd expect with the QGraphicsItem::DeviceCoordinateCache enabled.

This needs some investigation and can be tested on the kraken XBTUSD charts in particular. Enable profiling with chart --profile flag and watch how at some zoom levels the VWAP curve gets redrawn on every cursor move.

[goodboy]

Likely pertains to 9f5d0dd