OpenEuphoria

Re: Graphics help

• Posted by Robert Craig <rds at EMAIL.MSN.COM> Nov 15, 1998
• 520 views

David Cuny writes:
> I've been working on scrollbars in Dos32Lib, and I've got a question.
> Redrawing the scrollbars displays a lot of "flashing" as the graphics are
> redone. This is something which I would rather avoid.

If it's mainly a problem of "flicker" and not overall slowness,
there are some techniques you can try. (Maybe you've
thought of these already):

1. When updating an area of the screen, try to calculate the
     final picture of what it should look like before drawing it.
     Avoid displaying the intermediate stages. For
     example if you are moving an object, like a scroll bar, from
     point A to point B, an obvious solution is
     to "blank" it out at position A and  redraw it at B. This will
     cause flicker as the monitor will sometimes refresh when
     the bar is blanked out, before it has been redrawn. There
     would be far less flicker if you could redraw the image of
     the whole updated area in "one shot". i.e. draw the bar including
     some trailing "blank" pixels, to wipe out the previous image
     of the bar.

2. You might be able to update just the ends of the scroll bar, not the
     whole bar, to effectively move it.

3. You might wait for the vertical blank period of the monitor
     before updating the screen. There's some machine code for
     that around somewhere.

Regards,
     Rob Craig
     Rapid Deployment Software
     http://members.aol.com/FilesEu/