Scrolling smears controls
In my MDI app, when the user shrinks an MDI child form so scroll bars appear, then the uesr then drags the vertical scroll bar down, the contents of the form seem to get partially redrawn so they appear to stretch or smear at the bottom edge of the form. When the user stops the drag of the scrollbar, then the form draws itself and it looks fine.
What would cause the controls to not get re-drawn correctly on a scroll event? I would expect the contents of the form to move smoothly on a scrollbar drag as if it is larger than the container. But instead it looks like the form/contols are being partially drawn as the scrollbar is being dragged.
I was thinking I could register to listen to the scroll event, but I do not see any delegates for this when I am using the AutoScroll property of the form.
Any thoughts on how to make the scrolling look smooth?
thanks
Bryan
I think this happens because the redraw of the control occurs during idle time, and while scrolling quickly there isn't any. The scrolling actually does a bitblt to move as much of the window as is visible in both the before and after position. Then, the newly visible portion of the window is invalidated. Invalidate doesn't redraw immediately, but rather is cached until there is idle time to redraw the screen. If you want to force the draw, call the Update method on your Control or Form.
Unfortunately there isn't any scrolling event; you may have to override WndProc for the parent control and handle WM_VSCROLL and WM_HSCROLL to call Update.
Hope that helps!
