Contact visualizer crashes when using animation with start time higher than 0

[Vinggui]

I believe that there is a bug related to Meshcat animation recorder. This line of hydroelastic_contact_visualizer.cc and this line of point_contact_visualizer.cc send a time = 0, which, combined with a recording state, will force the animation to record this property. However, if we have used set_start_time() before, this line will crash the simulation.

How to reproduce

I am sorry that I don't have a ready to go example. Maybe I can build one soon, but I made a sequence that should probably crash:

• Start a simulation that contains an animation recording (spatula_slip_control?)
• Make the simulation run for some time and then call set_start_time( t>0 )
• Make some contact trigger contact visualizer, so that it draws its lines
• It should crash

Possible solution

Of course this crash is not intended, but I believe that these lines were trying to set time equal to the animation start time, not exactly 0. Hence, a solution would be:

• Getting the start_time() and then using that value in those lines.
• Treating time=0 as a possible input for int Frame()

@@ -42,6 +42,7 @@ class MeshcatAnimation {
int frame(double time) const {
    if (time == 0) { return 0; }
    DRAKE_DEMAND(time >= start_time_);
    return static_cast<int>(...);

What do you think?

[sherm1]

Not sure who to assign this to -- @SeanCurtis-TRI for disposition, please.