No way to directly set an existing QPixmap to a new QImage

There is no easy way to override an existing QPixmap with a new QImage without incurring the creation cost of a new pixmap with QPixmap::fromImage(). QPixmapData::fromImage() can modify a pixmap in-place, but this isn't accessible via the public API.

Proposal is to add QPixmap::setImage() to 4.7, and an internal qPixmapSetImage() to 4.6.x.