[Feature] Support DreamFusion

[LeoXing1996]

Thanks for your contribution and we appreciate it a lot. The following instructions would make your pull request more healthy and more easily get feedback. If you do not understand some items, don't worry, just make the pull request and seek help from maintainers.

Motivation

Support Dreamfusion. Refers to https://github.com/ashawkey/stable-dreamfusion

Who can help? @ them here!

BC-breaking (Optional)

Does the modification introduce changes that break the backward-compatibility of the downstream repositories?
If so, please describe how it breaks the compatibility and how the downstream projects should modify their code to keep compatibility with this PR.

Use cases (Optional)

If this PR introduces a new feature, it is better to list some use cases here, and update the documentation.

Checklist

Before PR:

• I have read and followed the workflow indicated in the CONTRIBUTING.md to create this PR.
• Pre-commit or linting tools indicated in CONTRIBUTING.md are used to fix the potential lint issues.
• Bug fixes are covered by unit tests, the case that causes the bug should be added in the unit tests.
• New functionalities are covered by complete unit tests. If not, please add more unit test to ensure the correctness.
• The documentation has been modified accordingly, including docstring or example tutorials.

After PR:

• If the modification has potential influence on downstream or other related projects, this PR should be tested with some of those projects.
• CLA has been signed and all committers have signed the CLA in this PR.

[codecov]

Codecov Report

Patch coverage: 19.77% and project coverage change: -1.72% ⚠️

Comparison is base (5b5f895) 82.23% compared to head (858a650) 80.52%.

❗ Current head 858a650 differs from pull request most recent head a234d8e. Consider uploading reports for the commit a234d8e to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1563      +/-   ##
==========================================
- Coverage   82.23%   80.52%   -1.72%     
==========================================
  Files         416      425       +9     
  Lines       27960    28747     +787     
  Branches     4374     4461      +87     
==========================================
+ Hits        22994    23148     +154     
- Misses       4026     4658     +632     
- Partials      940      941       +1     

Flag	Coverage Δ
unittests	80.52% <19.77%> (-1.72%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files Changed	Coverage Δ
mmagic/models/editors/dreamfusion/renderer.py	13.88% <13.88%> (ø)
mmagic/models/editors/dreamfusion/camera.py	15.47% <15.47%> (ø)
mmagic/models/editors/dreamfusion/dreamfusion.py	16.00% <16.00%> (ø)
mmagic/models/editors/dreamfusion/vanilla_nerf.py	19.62% <19.62%> (ø)
...ls/editors/dreamfusion/stable_diffusion_wrapper.py	23.40% <23.40%> (ø)
mmagic/engine/hooks/dreamfusion_hook.py	28.94% <28.94%> (ø)
mmagic/datasets/dummy_dataset.py	38.09% <38.09%> (ø)
mmagic/models/utils/tensor_utils.py	75.00% <50.00%> (-25.00%)	⬇️
mmagic/models/editors/dreamfusion/activate.py	69.23% <69.23%> (ø)
mmagic/datasets/__init__.py	100.00% <100.00%> (ø)
... and 3 more

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[junshutang]

Add occupancy grid transmittance estimator for spatial skipping. "nerfacc.OccGridEstimator(roi_aabb, resolution, levels)"

[junshutang]

Sampling with spatial skipping.

ray_indices, t_starts, t_ends = grid.sampling(rays_o, rays_d, render_step_size=1e-3)
t_mid = (t_starts + t_ends) / 2.0
sample_locs = rays_o[ray_indices] + t_mid * rays_d[ray_indices]