optimizing point lights

[miangoleh]

I am trying to optimize the position of a bunch of point lights in the scene. I was wondering if there is a consideration with regard to the integrator choice. I am using path but I wasn't sure if I should use a projective integrator instead?

[njroussel]

Hi @miangoleh

Point lights' positions aren't differentiable, regardless of the integrator choice. In the documentation, for each plugin their is a "Flags" column which, among other stuff, will indicate if the parameter is differentiable or not.

[miangoleh]

Although documentation is showing them as not differentiable, printing the model params indicates the differentiable flag and gradients are indeed computed and optimized.

[njroussel]

Do you mind sharing some code? It really shouldn't be displaying itself anywhere as differentiable.

[miangoleh]

I am putting point lights using this code:

light_dict = {
  'type': 'point',
  'position': light_positions[i],
  'intensity': {
      'type': 'rgb',
      'value': [value_normalized, value_normalized, value_normalized],
  }
}

And then adding their position and intensity to the optimizer using this

opt[f'light{light_idx}.position'] = scene_params[f'light{light_idx}.position']
opt[f'light{light_idx}.intensity.value'] = scene_params[f'light{light_idx}.intensity.value']

I tried printing out grads using "dr.grad(opt[light0.position])". It is definitely computing grads with "path" or "prbvolpath" as the integrator but with "prb_projective" all grads are zero.

I don’t see the differentiable flag anymore. It could be a lapse in my memory, or perhaps it was removed in a recent update—I remember seeing it a few months ago.