[Ardour-Dev] SuperRapidScreenUpdates are neither rapid, nor super.

Paul Davis paul at linuxaudiosystems.com
Sun Mar 8 06:59:25 PDT 2009

On Sat, Mar 7, 2009 at 11:21 PM, David Taht <d at teklibre.com> wrote:

> I am going to disagree with this slightly. If you are doing different
> kinds of updates to the screen it helps to be sending the draw commands
> as fast as possible, so that the display hardware has smaller chunks to
> render at a time.

video hardware works like audio hardware. it redraws at a fixed frequency,
by painting an offscreen framebuffer to the real framebuffer. your
description makes no sense to me. rendering is done on a schedule determined
by the hardware (just as with audio), its not based on what software is (or
is not) doing. between two video vertical retraces, the h/w is busy
rendering into the offscreen buffer; when the retrace starts, the video
drawing h/w starts rendering what was the offscreen buffer to the pixels,
and the rendering h/w switches to use what used to be the "real"
framebuffer. the buffer switching is not necessarily literally like this
(video RAM is special), but conceptually, this is what is happening. you can
feed stuff in bits and pieces to the renderer, or in big chunks - either way
its not going to display stuff till the next vertical retrace begins.
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