[SDL] Double buffering waitretrace and flickering

Michele Bini mibin at tin.it
Sat Aug 28 05:43:32 PDT 1999


On Fri, Aug 20, 1999 at 08:49:26PM -0700, Gary Scillian wrote:
> Just to add another data point on this:
> 
> I'm using an old ATI Rage card, using the XFree86-Mach64-3.3.2-8
> driver.  I'm using a 1024x768 16bpp visual as my default.
> 
> The plasma demo clearly shows tearing, regardless of the options
> specified, when run as root and fullscreen.

It is harder, but you can notice tearing even in a window.
It can be avoided if you slow down the movement of the plasma
to reduce the differencies of one frame to another.
When I wrote that demo it was intended to run at around
20 fps (on a 486 33 Mhz), and I was too lazy to implement timing.

What is happening is that the application is updating the screen
faster than the video refreshes it, so that the upper part of
the screen contains an older frame than the lower one, (or the
opposite), or that the screen refreshes itself when the video
memory is only half updated (this is expecially true in hw,
non double buffering mode).

I will hopefully reduce this problem soon.

-Michele



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