Cycles: Multi-scale Principled Hair Huang Model #116094

Weizhen Huang · 2023-12-12T13:22:22+01:00

Weizhen Huang commented

2023-12-12 13:22:22 +01:00

Modify Principled Hair Huang model so that it also works for nearfield.
This is done by computing the actual range of the hair width that the current pixel covers, and only integrate on that subset.
When the hair covers less than one pixel on the screen or when the ray is not a camera ray, the model works the same as before.

Compare with previous model (elliptical cross-section)

Before	After

Compare with Chiang (circular cross-section)

Chiang	Huang

Modify Principled Hair Huang model so that it also works for nearfield. This is done by computing the actual range of the hair width that the current pixel covers, and only integrate on that subset. When the hair covers less than one pixel on the screen or when the ray is not a camera ray, the model works the same as before. ### Compare with previous model (elliptical cross-section) |Before|After| |--|--| |![before](attachments/f00ac81e-1cbd-4458-a8af-088e7a906be2)|![after](attachments/d587daa6-a5e7-43a5-8180-0a22136dc036)| ### Compare with Chiang (circular cross-section) |Chiang|Huang| |--|--| |![chiang](attachments/157b355c-9fa8-486c-901c-863d56495dc7)|![huang](attachments/4193a7ff-37de-44da-8e1e-9fe351db03cf)|

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Weizhen Huang added this to the Render & Cycles project 2023-12-12 13:22:43 +01:00

Weizhen Huang force-pushed hair-nearfield from f4db5443d3 to de2a33f456

2024-02-08 12:23:27 +01:00

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Weizhen Huang force-pushed hair-nearfield from 9e6d181223 to ee32d28422

2024-02-09 22:59:17 +01:00

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Weizhen Huang force-pushed hair-nearfield from cd8450b2b2 to d21f817e7e

2024-02-12 17:59:55 +01:00

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Weizhen Huang changed title from ~~WIP: Cycles: Multi-scale Principled Hair Huang Model~~ to Cycles: Multi-scale Principled Hair Huang Model

2024-02-12 18:35:48 +01:00

Weizhen Huang commented

2024-02-12 20:34:49 +01:00

For review:

The first three commits are just improvements/simplifications to make the following change easier. The commit messages should be enough to explain what they do. They will be committed separately.

The last commit is the main implementation of the pull request. The algorithm is similar as in An Efficient and Practical Near and Far Field Fur Reflectance Model: In sum/closure.h/osl/closure_setup.h, one computes the projected width of a pixel at the shading point; in bsdf_principled_hair_huang.h, this pixel width is compared with the width of the hair; if the hair spans more than one pixel, one only integrates in the range that a pixel would cover at the shading point, instead of the whole hair width.

**For review:** The first three commits are just improvements/simplifications to make the following change easier. The commit messages should be enough to explain what they do. They will be committed separately. The last commit is the main implementation of the pull request. The algorithm is similar as in [An Efficient and Practical Near and Far Field Fur Reflectance Model](https://sites.cs.ucsb.edu/~lingqi/publications/paper_fur2.pdf): In `sum/closure.h`/`osl/closure_setup.h`, one computes the projected width of a pixel at the shading point; in `bsdf_principled_hair_huang.h`, this pixel width is compared with the width of the hair; if the hair spans more than one pixel, one only integrates in the range that a pixel would cover at the shading point, instead of the whole hair width.

Weizhen Huang force-pushed hair-nearfield from d21f817e7e to 54b431e76d

2024-02-12 20:34:55 +01:00

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Weizhen Huang requested review from Brecht Van Lommel 2024-02-12 20:37:47 +01:00

Weizhen Huang requested review from Lukas Stockner 2024-02-12 20:37:57 +01:00

Weizhen Huang referenced this pull request

2024-02-13 22:03:06 +01:00

Microfacet-based PrincipledHairBSDF #111257

Brecht Van Lommel approved these changes 2024-02-20 18:44:35 +01:00

Weizhen Huang force-pushed hair-nearfield from 54b431e76d to e3abd15692

2024-02-22 17:37:45 +01:00

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