When using the Gantt_OnTimeItemAreaPaintBackground event to draw things on the gantt chart what is the difference between using the aOffscreenDraw.Graphics object and e.G object. Both seem to work OK on the gantt chart but only the e.G works with the print preview. If I use the aOffscreenDraw.Graphics then the print preview does not show any of the items that I have drawn. Why?
You should use the Graphics object sent in to the event (e.G). The OffscreenDraw.Graphics is used to render the offscreen image produced by the Gantt. When you print you never render the result to the screen, and we send the rendered image to Graphics object you provide in the Print call.
So things you draw to OffscreenDraw.Graphics directly is never really part of the Gantt, but rather put on top of the Gantt (and we only send the Gantt to the printer).