Comment 3 for bug 550449

This problem is two-fold:

1) The slider itself uses a delayed update policy, meaning that the update signal to redraw the goocanvas is emmitted only every now and then while dragging. Changing the policy is easy to do in the UI files.

2) When changing the slider's update policy the redraw (effectively the Render() method in the sequence class) is invoked continuously while dragging which results in some serious flickering.

Fortunately, there is a solution to (2) as well: simply temporarily postponing redraws while the goocanvas is being redrawn. Then allowing a redraw once the goocanvas contents have been rebuild.

I've attached a patch which enables smooth zooming via the zoom scroller.