PBD + MPM examples

[zzigak]

Added the following examples:

• XPBD cloth (bending and stretching constraints)
• XPBD mesh (volumetric constraints, edge constraints, and hash skinning for speedup).
• PBF fluid simulation
• MPM viscoplastic model

[liminchen]

When I try to run the pbf example, I got

[Taichi] version 1.7.2, llvm 15.0.5, commit 0131dce9, osx, python 3.11.9
[Taichi] Starting on arch=metal
Traceback (most recent call last):
  File "/Users/minchen/Desktop/solidSimBook/code/14_pbf/simulator.py", line 519, in <module>
    main()
  File "/Users/minchen/Desktop/solidSimBook/code/14_pbf/simulator.py", line 506, in main
    scene.lines(np.array([start_corner, end_corner], dtype=np.float32), color=(0.6, 0.6, 0.6), width=1)
  File "/Users/minchen/Library/Python/3.11/lib/python/site-packages/taichi/ui/scene.py", line 166, in lines
    copy_all_to_vbo(vbo, vertices, 0, 0, per_vertex_color if has_per_vertex_color else 0)
  File "/Users/minchen/Library/Python/3.11/lib/python/site-packages/taichi/lang/kernel_impl.py", line 1113, in wrapped
    return primal(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/minchen/Library/Python/3.11/lib/python/site-packages/taichi/lang/kernel_impl.py", line 1043, in __call__
    key = self.ensure_compiled(*args)
          ^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/minchen/Library/Python/3.11/lib/python/site-packages/taichi/lang/kernel_impl.py", line 1009, in ensure_compiled
    instance_id, arg_features = self.mapper.lookup(args)
                                ^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/minchen/Library/Python/3.11/lib/python/site-packages/taichi/lang/kernel_impl.py", line 513, in lookup
    if key not in self.mapping:
       ^^^^^^^^^^^^^^^^^^^^^^^
TypeError: unhashable type: 'numpy.ndarray'

I guess this might be a python version issue. Which python are you using?

[zzigak]

Hi Minchen, sorry, I should have specified the version! Just created a new environment with python 3.10.17 from scratch and this works for me:

(test_pb) ➜ zzigak @ mbp ~/test_pb uv pip list                                                                                                                               git:(main)
Package        Version
-------------- -------
colorama       0.4.6
dill           0.4.0
markdown-it-py 4.0.0
mdurl          0.1.2
numpy          2.2.6
pygments       2.19.2
rich           14.2.0
taichi         1.7.4

I think the crash occurs because Taichi v1.7.2 fails to recognize the NumPy array as a data container (runtime argument), incorrectly treating it as a template argument that requires hashing

For visualization i recommend putting the window into full screen for proper rendering of particles. Please do tell if this works for you!

[zzigak]

The same version works for pbd_cloth (need to add warp-lang) example and viscoplastic mpm example too. For pbd_cloth you need to enable animation first before moving the control point, but it should be a simple fix to only allow that button to work when animation is enabled.