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Add notes about Ray Portal BSDF quirks #104807

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Brecht Van Lommel merged 3 commits from Alaska/blender-manual:portal-notes into main 2024-06-04 17:06:07 +02:00
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Alaska commented 2024-06-04 07:37:38 +02:00
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Alaska added 1 commit 2024-06-04 07:37:40 +02:00
Alaska requested review from Aaron Carlisle 2024-06-04 07:38:01 +02:00
Alaska requested review from Lukas Stockner 2024-06-04 07:38:18 +02:00
Alaska requested review from Brecht Van Lommel 2024-06-04 07:38:24 +02:00
Alaska commented 2024-06-04 07:42:18 +02:00
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In the pull request for the Ray Portal BSDF and in some bug reports, various people directly or indirectly asked for help with understanding the Ray Portal BSDF. The main things they people didn't seem to realize was:

  1. The Ray Portal BSDF only allows rays to travel through it in one direction.
  2. That light passing through a portal will be noisy because Cycles Next Event Estimation does not work through portals (This is one of the "techniques" that does not work through portals, I can't recall if there are other techniques that don't work).

This pull request adds notes for both.

On a side note, I have said that some techniques do not work through the portal rather than Next Event Estimation doesn't work through portals. This is because because I feel like it may be too technical for the manual, or more specifically, this page of the manual. If you feel other wise, then just say so.

In the [pull request for the Ray Portal BSDF](https://projects.blender.org/blender/blender/pulls/114386) and in some bug reports, various people directly or indirectly asked for help with understanding the Ray Portal BSDF. The main things they people didn't seem to realize was: 1. The Ray Portal BSDF only allows rays to travel through it in one direction. 2. That light passing through a portal will be noisy because Cycles Next Event Estimation does not work through portals (This is one of the "techniques" that does not work through portals, I can't recall if there are other techniques that don't work). This pull request adds notes for both. On a side note, I have said that some techniques do not work through the portal rather than Next Event Estimation doesn't work through portals. This is because because I feel like it may be too technical for the manual, or more specifically, this page of the manual. If you feel other wise, then just say so.
Brecht Van Lommel requested changes 2024-06-04 16:08:52 +02:00
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We also really need some images and example node set up on this page, but I haven't gotten to it yet.

We also really need some images and example node set up on this page, but I haven't gotten to it yet.
manual/render/shader_nodes/shader/ray_portal.rst Outdated
@ -17,1 +17,4 @@
.. note::
- The portal only allows rays to pass through in one direction.
Brecht Van Lommel commented 2024-06-04 16:06:06 +02:00
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I would add:

Add a second portal at the target location to make rays go in the other direction as well.

I would add: > Add a second portal at the target location to make rays go in the other direction as well.
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manual/render/shader_nodes/shader/ray_portal.rst Outdated
@ -18,0 +19,4 @@
- The portal only allows rays to pass through in one direction.
- Some of the techniques Cycles uses to reduce noise does not work through portals.
Brecht Van Lommel commented 2024-06-04 16:08:26 +02:00
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I suggest:

Light sampling does not work efficiently through portals. This can lead to increased noised from lights on the other side of portals. Particularly small lights may be very noisy, or not pass through at all.

I suggest: > Light sampling does not work efficiently through portals. This can lead to increased noised from lights on the other side of portals. Particularly small lights may be very noisy, or not pass through at all.
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Alaska added 1 commit 2024-06-04 16:16:44 +02:00
Alaska commented 2024-06-04 16:19:55 +02:00
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We also really need some images and example node set up on this page.

I can work on this tomorrow if you'd like. Do you have a list of examples you'd like? The main one I can think of is using vector math nodes to offset the ray to somewhere else (See attached image)

> We also really need some images and example node set up on this page. I can work on this tomorrow if you'd like. Do you have a list of examples you'd like? The main one I can think of is using vector math nodes to offset the ray to somewhere else (See attached image)
Ray portal example setup.jpg
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Ray portal example setup.jpg
Alaska added 1 commit 2024-06-04 16:23:11 +02:00
Brecht Van Lommel commented 2024-06-04 16:29:42 +02:00
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Maybe there could be an example of a group node that takes a position and rotation of the target portal as input? I'm not sure if it's possible to create a relatively node setup for a screenshot for that (say max 10 nodes).

If not just a position offset seems fine.

For the images, I think images like the TV and the orange/blue portals are fine concepts. But maybe the framing and lighting could be better.

Maybe there could be an example of a group node that takes a position and rotation of the target portal as input? I'm not sure if it's possible to create a relatively node setup for a screenshot for that (say max 10 nodes). If not just a position offset seems fine. For the images, I think images like the TV and the orange/blue portals are fine concepts. But maybe the framing and lighting could be better.
Brecht Van Lommel approved these changes 2024-06-04 16:30:04 +02:00
Brecht Van Lommel merged commit 940df7e6bd into main 2024-06-04 17:06:07 +02:00
Brecht Van Lommel deleted branch portal-notes 2024-06-04 17:06:08 +02:00
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Reference: blender/blender-manual#104807
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