Real-time clock: Prototype Todos #105732
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Reference: blender/blender#105732
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UI and operators for starting/stopping the real time clock
Add a timer variable likeScreen::animtimer. If it exists the realtime clock is running.Use the
animtimerfor both anim playback and realtime clock. Separate flag indicates which clocks as currently running.ScreenAnimData)ED_functions for creating/destroying the timer and checking state (likeED_screen_animation_play,ED_screen_animation_playing)SCREEN_OT_animation_play,SCREEN_OT_animation_cancel)Screen.is_animation_playing)Timer events and depsgraph trigger
animtimerwhich just check for running playback with a ED_screen function (except the 2 cases in sound and sequencer which directly access DNA, those need to check theactive_clockflag).SCREEN_OT_animation_step). Keymap entry to invoke this operator throughTIMERevents. DoesTIMER0work here or do we need to useTIMER1,TIMER2, or add a new event type?ED_function to prepare depsgraph updates on realtime clock events (likeED_update_for_newframe).DEG_graph_time_tag_updatewith a time source type to distinguish between updates from animation and from the realtime clock.Depsgraph nodes and relations
TimeSourceNodeto depsgraph that can be distinguished from the current time source. Animated IDs, properties, etc. will keep their relation to the current time source ("animation source"?), while simulations can be moved gradually over to using the new realtime source.A problem i'm trying to solve:
The animation playback timer and the realtime clock timer should be "in phase" as much as possible to avoid very frequent depsgraph updates over tiny time steps.
Note that i'm not talking about tying the playback of the realtime clock to the timeline or vice versa, just the case where both animation and realtime clock are running simultaneously. In this situation the animation clock will use the RenderSettings fps value as usual, but could the realtime clock run at a different interval? (eek!)
Even when both clocks always use the same time step size, they might still be started individually and thus be out of phase. Then the depsgraph has to perform 2 updates over the course of 1 frame because both animation and realtime clock trigger it (albeit with different tagged objects based on dependencies).
The simplest solution would be use the same timer for both clocks. As a consequence there might be a delay of up to 1 frame when starting animation playback or the realtime clock because the timer might already be running, but i think that's acceptable.
Simulation Nodes: Realtime clock documentationto Real-time clock: Prototype TodosCreated a separate task for "locking" the realtime clock to the scene timeline: #106182
On the topic of calculating time steps (aka. "delta time") from absolute values:
The way simulations currently work is based on storing a last update time locally. The naming is different for each simulation system, but the principle is the same, for instance:
RigidBodyWorld::ltimeParticleSystem::cfraCloth::last_frameWhen the respective update function is called, each system will compute a time step based on the current scene time (
scene.r.cfra,BKE_scene_ctime_get, etc.) and the differencedtime = new_time - old_time.To get this working with as little change as possible i can store a "cfra" value for the realtime clock as well (somewhere in
Scene). The current time in seconds can be calculated for the realtime clock just like the scene clock by multiplying with the current fps setting. It must be noted that the realtime clock'scfrais not a meaningful value by itself, it should only be used to calculate delta time (and possibly for randomization seeds if determinism is not a requirement).There is a risk that changing fps settings could alter the absolute time such that simulations see a sudden jump of the time step, but it seems this would already be a problem with current simulations, so it's not a regression (simulations just need to reset when fps changes). Storing and integrating a float/double time value instead of a frame count might avoid this, but could lead to lower time accuracy the further the simulation progresses.