RFC: dragging plots around

[ColinJDenman]

At the moment, in plot view, I find that if I want to nudge the viewport around, I either have to use the Shift-Number keys or drag the display with a finger.

With the latter, I find that as soon as I've dragged the display by a pixel, it goes off and redraws. Some plots can take a long time to draw, so effectively the drag is terminated.

I would like the calculator to hold off on the redraw until the user completes the drag operation and removes their finger from the display. The existing graphic should still drag around to aid positioning, but the redraw should be held off until the user interaction is complete.