Change and show geometry color dynamically

[Yury G.]

Hi!
I have a loop in which I'd like to change a color of a geometry (after some conditions are met) and show it in visualizer. So I have something like this:

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while (true)
{
    ...
    if (some condition)
    {
        auto& body = m_model.updBodySet().get("my_fancy_body");
        auto& offsetFrame = body.updComponent<PhysicalOffsetFrame>("fancy_offset_frame");
        auto& geom = offsetFrame.upd_attached_geometry(0);
        std::cout << geom.getName() << " " << geom.getColor() << std::endl;
        geom.setColor(Green);
        std::cout << geom.getName() << " " << geom.getColor() << std::endl;
    }
    ...
    m_model.getVisualizer().show(state);
}

The output from this code is:

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arm_r_geom_1 ~[1,0.5,0]
arm_r_geom_1 ~[0,1,0]

but in visualizer the color is still the same. Is such a use-case possible at all?

[Ayman Habib]

Hi Yuri,

You apparently are caching the model's state outside the loop. Whatever changes you make to the model in the loop have no effect until you call model's initSystem or some realization method that pushes values to the state. Since you're calling updXX() methods these actually invalidate the system underneath the model so the code should throw an exception if you try to do something that utilizes the system rather than just show the state in the visualizer.

Hope this helps,
-Ayman

[Yury G.]

Thank for a quick reply, Ayman!
So if I understood correctly calling

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m_model.updMultibodySystem().realizeModel(state);

after making changes to a model should help, but it doesn't.
Also maybe there is some more "right" path to follow here in order to dynamically visualize flashing spheres in OpenSim? I saw some *DecorativeGeometry* classes in Simbody, but looks like it isn't implemented in OpenSim yet.

[Ayman Habib]

Hi Yury,

The safest way to propagate changes made to the model into a state object is to call initSystem which will return a new instance of the state consistent with the model, other methods are intended for finer granularity changes/calculations.

DecorativeGeometry subclasses are the primitives that OpenSim GUI and API visualizer work with, as such they are not exposed to users in XML, instead we have Sphere, Cylinder, ... as OpenSim Geometry abstractions that get mapped to the corresponding DecorativeGeometry classes before being sent to visualization.

Hope this helps,
-Ayman