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

Paul Davis paul at linuxaudiosystems.com
Sun Mar 8 06:54:58 PDT 2009

On Sun, Mar 8, 2009 at 7:07 AM, Fons Adriaensen <fons at kokkinizita.net>wrote:

> It shouldn't be a CPU hog. Yass (scrolling scope) running
> full-screen, 100 updates/second,

how does it accomplish this on an 80Hz monitor?

You need to repaint only two narrow vertical strips,
> the new part at the right, and the one that was covered
> by the playhead in it previous position. The important
> part is to structure your display code in such a way
> it can do this efficiently.

the problem is that its not always "your" display code that is the problem.
we reworked the canvas display logic to avoid a very nasty problem with X &
the GnomeCanvas. the Canvas has no concept of "zoom, keeping the center of
the current display in the center". to make that happen with "naive" Canvas
code you end up with a window move and then a redraw (move to reposition so
that when the redraw is done, the correct part of the window is visible.
because X is async, you can sometimes (often!) see the intermediate state
between the window move and the redraw. nick redesigned how things happen so
that this problem is completely avoided (basically, never using Canvas
scrolling) but it would not suprise me if this has broken the "stationary PH
option" which explicitly scrolled the entire canvas window. note that this
behaviour does not occur on OS X where their windowing architecture is so
explicitly double-buffered that its impossible to see "intermediate" states
(well, nothing is impossible, but ...)

there is no question of us going back to the old scrolling stuff - it led to
absolutely horrible visual results when zooming with anything except the
left edge of the screen as the zoom "anchor" point. the real future here is
in a new canvas entirely, and although once that seemed as though it would
certainly be a part of the ardour 3.0 development path, but that is not the
case and i honestly do not when it might happen. it does need to though, for
a variety of other reasons as well as this one.
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