Implement SetAnimation in Meshcat C++

[DamrongGuoy]

Please let me know if this issue is really not an issue. I'm not familiar with MeshCat, so I might misunderstand.

History

I am using //tools:drake_visualizer with lcm-logplayer-gui like this:

bazel run //tools:drake_visualizer &
bazel build @lcm//:lcm-logplayer-gui
bazel-bin/external/lcm/lcm-logplayer-gui  <my_lcm-log_file_from_my_simulation> &

It is very convenient to playback LCM messages without actually running the simulation again. The lcm-logplayer-gui allows me to play slower, faster, or to pause at a certain time step. I can adjust visualization settings and replay again.

Request

Ideally I would like MeshCat to listen to LCM messages from lcm-logplayer-gui too. However, I will accept any solution that allows me to do similar things.

Edit (9/21/21 3:27 PM PT)

@RussTedrake already showed me via compass_gait.html that we already had most of my requests. This issue only need to track the SetAnimation method in the c++ Meshcat feature.

[RussTedrake]

I see. Meshcat doesn't use lcm, so lcm logs aren't going to do the job.

Instead, we can record (and playback) animations. Here is an example: https://people.csail.mit.edu/russt/uploads/compass_gait.html

Click "Open Controls" and you will see play/pause/reset and a time slider all available for you. Implementing the SetAnimation method in the c++ Meshcat is the next (and one of the last) main features I need to reimplement in c++. I'm happy to have an issue to track it.

[DamrongGuoy]

@RussTedrake . Thank you very much. Indeed the compass_gait.html example already answered most of my questions.

I have updated the request to say it's almost there already!

[SeanCurtis-TRI]

@RussTedrake This (recording animations) presumably works fine for the poses of frames, but as we add support for visualizing contact surfaces and the like, I presume we're going to need a different mechanism, right?

I believe that's something that @DamrongGuoy's lcm-based workflow gets him for free.

All of this would probably be resolved if we had (in Drake) the ability to simply save entire contexts and then play them back. But I believe that's still a large, distant endeavor.

[RussTedrake]

Just to be clear -- if someone wants to visualize the results of a lcm log file (e.g. of estimated robot state) in meshcat instead of drake visualizer, there is no impediments to that. In both cases, you would use lcm-logplayer-gui to play the state messages, and have a small drake app that subscribes to that lcm and publishes to meshcat.

The only thing that is different here is if you were relying on some lcm viewer draw message in your log files reproducing the visualization directly to drake visualizer; that part won't work with meshcat.

(I had a hallway conversation with someone a few days ago that made me realize this should be clarified).

I've updated the issue title to reflect my intention to only resolve this, right now, by implementing SetAnimation. @DamrongGuoy -- if you feel that this does not capture the intention of your issue, then feel free to rename it again, but then you'll need assign it to someone else. ;-)