JDK-8210547[linux] Uncontrolled framerate, general frame sync/over-calculating animations

[Michael Zucchi]

Morning list!

I hit the above bug[1] a little while ago while using a Transition for 
timing on a couple of GNU/Linux systems [2,3].  Basically it runs 
flat-chat because each interpolation call makes changes which triggers a 
new render pass which then re-runs the animators if they're active, 
which retriggers another render pass and so on. Trivial example that 
demonstrated is below.  If you set a specific frame-rate in the 
constructor then it doesn't occur. None of the related system properties 
seem to have any effect.  Tracing through the code I couldn't see how 
this doesn't always happen with X11/OpenGL, plus there seems to be a 
bunch of stale/unfinished frame throttling code that never gets run.  I 
also noticed that gdk_timer was used for frame timing, but this is 
documented as not being suitable for this task - it lacks suitable 
resolution and must be reset each call guaranteeing drift.  And in any 
event timing unlinked from the display will never be accurate.

I developed a small patch to use GLX_SGI_video_sync to synchronise to 
the actual video frame-rate.  It's probably hooked into the wrong place 
but i'm not very familiar with the code and couldn't find much 
documentation on the internals of prism and quantum toolkit; I've 
attached it as a matter of interest.  With this patch enabled multiple 
windows will render smoothly matching the video frame rate exactly and 
the animation calculations are only invoked once per frame apart from 
wrap-around of cyclic animations (I've only tested with simple scenes).

The main drawback is added latency for low-frame rate monitors (I've 
tested with a system that can do anything from 25 to 150), and the 
'animation now timestamp' is calculated ad-hoc rather than syncing to 
the expected presentation time.  Having to call glXMakeContext extra 
times isn't very cheap either, but it's already being called a lot.

With some guidance/pointers I can look further if it would be of use to 
the project.

Regards,
  Michael Z

[1] https://bugs.openjdk.org/browse/JDK-8210547
[2] gentoo, liunux 6.12.36, AMD Ryzen 4700U APU.
[3] slackare64-current linux 6.12.29, Ryzen 3900X, Radeon HD7970.

--
             Group g = new Group(new Text("Hello"));
             g.setTranslateX(100);
             g.setTranslateY(100);
             root.getChildren().setAll(g);
             Transition anim = new Transition() {
                 double arg = 0;

                 {
                     setCycleCount(INDEFINITE);
                     setCycleDuration(Duration.seconds(1));
                 }

                 @Override
                 protected void interpolate(double frac) {
                     g.setRotate(arg++);
                 }
             };
             anim.play();
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