Q3Canvas problem (zoomed in drawBackground)

[Pieter from Belgium]

While migrating to Qt 4, a QCanvas subclass became a Q3Canvas subclass. The behaviour of drawBackground seems to have changed. When zoomed in and scrolling, drawing is clipped somewhat at the borders.

This is illustrated in the following screenshot:



There is a small white border between the visible content pixels and the scrollbars.
When scrolling, this gives rise to a more or less regular pattern of horizontal resp. vertical white bars.
I am certain that I do draw the missing pixels to the painter, but the seem to disappear. (In fact, for certainty I first extend the clip with 10 pixels in each direction...)

Has something changed that I am not aware of?