Optimizing Transform4f

[zichenwang01]

Hi,

I wrote a simple example of optimizing a custom class but encountered some problems when using mi.traverse(). Here are my tiny reproducer and the error message that I got. I have tested on RTX A6000 and LLVM. Also, it would be very helpful if I could ask how I should write the parameters_changed() functions corresponding to this traverse() function. Many many thanks!

import drjit as dr
import mitsuba as mi

mi.set_variant('cuda_ad_rgb')
# mi.set_variant('llvm_ad_rgb')

class T():
    def __init__(self, transform:mi.Transform4f):
        self.transform = transform
        
    def traverse(self, callback):
        callback.put_parameter("p", self.transform.matrix[1, 3], mi.ParamFlags.Differentiable)
    
    # def parameters_changed(self, keys):
    #     self.transform.matrix = 

p = mi.Float(0.1)
dr.enable_grad(p)

transform = mi.Matrix4f([[1, 0, 0, 0],
                         [0, 1, 0, p],
                         [0, 0, 1, 0],
                         [0, 0, 0, 1]])
transform = mi.Transform4f(transform)
t = T(transform)

params = mi.traverse(t)
print("params", params)
exit(0)

the error message

params Traceback (most recent call last):
  File "/home/zw336/IR/bp/tmp.py", line 28, in <module>
    print("params", params)
  File "/home/zw336/.conda/envs/diff-sdf/lib/python3.11/site-packages/mitsuba/python/util.py", line 116, in __repr__
    param_list += f'  {k:{name_length}}  {flags_str:7}  {type(value).__name__:{type_length}} {node.class_().name()}\n'
                                                                                              ^^^^^^^^^^^
AttributeError: 'T' object has no attribute 'class_'. Did you mean: '__class__'?

[rtabbara]

Hi @zichenwang01 ,

Your custom class needs to be a subclass of mi.Object

class T(mi.Object):
    def __init__(self, transform:mi.Transform4f):
        self.transform = transform
        super().__init__(self)
        
    def traverse(self, callback):
        callback.put_parameter("p", self.transform.matrix[1, 3], mi.ParamFlags.Differentiable)

Hopefully your traversal should then work

[zichenwang01]

Thank you!