Foreground Shader selection from tsxAPI?

[borgcone]

In the Model side of tS7.x or tS5/6, how can we switch the mode of "Foreground Effects Shader" (e.g. to "Simple Volumetric") from a plugin?

After I selected the mode by clicking the button, I can get/set the parameter value using tsxScene[GS]etShaderXXXXXX() API functions. But I would like to manipulate the mode from my model-side plugin instead of mouse-click.