[example] Ti-example: instant ngp renderer

[Linyou]

Add a file for ti-example: instant ngp renderer.
For more details, please visit https://github.com/Linyou/taichi-ngp-renderer.

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[neozhaoliang]

This is the error when running on my laptop (ubuntu22.04 + intel(GT2) card) using the vulkan backend, have no idea what it's about:

Loading model from ./npy_models/lego.npy
GridEncoding: base resolution: 16, log scale per level:1.31951 feature numbers per level: 2 maximum parameters per level: 524288 level: 16
[W 11/20/22 17:02:25.353 3632306] [type_check.cpp:visit@164] [$4178] Field index 0 not int32, casting into int32 implicitly
File "/home/zhao/China_R_Meeting/taichi_ngp.py", line 472, in raymarching_test_kernel:
                occ = self.density_bitfield[ti.u32(
                      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
                    idx // 8)] & (1 << ti.u32(idx % 8))
                    ^^^^^^^^^^

[E 11/20/22 17:02:43.171 3632306] [vulkan_device.cpp:submit@1720] Vulkan Error : -4 : failed to submit command buffer


[E 11/20/22 17:02:43.171 3632306] [ir.cpp:~DelayedIRModifier@411] Assertion failure: to_insert_before_.empty()


terminate called after throwing an instance of 'std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >'

Changing u32 to int does not work either.

[Linyou]

Hi @neozhaoliang.

The code is running fine on my machines (mac and PC laptop with Vulkan), so I am not sure what is happening here. However, I have fixed the type warning that line 472 produce, hope this change can fix the error.

In my experience, the Vulkan backend may crash when doing multiplication using types float32 and float16, in which the types are mismatched. Maybe, the reason for this error is something similar.

[neozhaoliang]

It still crashes.

Some nits:

1. this example has keyboard control interfaces, could you please add a helper docstring at the beginning of the file, so that users can know how to play with it?
2. our CI bot uses pylint to check the coding style, renaming built-in names like input would fail the test, could you please choose other variable names to avoid this?

[Linyou]

It still crashes.

Some nits:

1. this example has keyboard control interfaces, could you please add a helper docstring at the beginning of the file, so that users can know how to play with it?
2. our CI bot uses pylint to check the coding style, renaming built-in names like input would fail the test, could you please choose other variable names to avoid this?

Does intel(GT2) card support SharedArray?

Also, I have added the instruction of GUI to the beginning of the file and changed the variable names for pylint test.

[neozhaoliang]

LGTM!