AO Detail Map

[Mistale]

Fixes #4807
Uses the concepts introduced by #1968.

PR adds the following properties to pc.StandardMaterial with documentation and tests:

• aoDetailMap (texture)
• aoDetailMapChannel ("r", "g", "b", "a", default is "g")
• aoDetailMapUv (number)
• aoDetailMapTiling (vec2)
• aoDetailMapOffset (vec2)
• aoDetailMode (pc.DETAILMODE_*)

When combined with a baked aoMap, this PR allows for high- and low-frequency AO to be mixed without requiring excessively large baked textures. Typical use-cases may be a fence, a car grille or similar where one might want to use a baked AO texture for the entire object, but use a tiling baked AO texture for the intricate details.

Example:

From left to right: baked AO, baked AO + detail Normal, baked AO + detail Normal + detail AO

I confirm I have read the contributing guidelines and signed the Contributor License Agreement.

[slimbuck]

Hi @Mistale,

Sorry for our slow response on your PR - it's awesome, so we'll review/test/merge real soon.

Thanks!!

[mvaligursky]

This should mention the default value is 'g'

[Maksims]

Is it common to use default value 'g' instead or 'r' in other similar properties?
We should avoid making assumptions of how artist should pack their channels, even as a default option while it is configurable.

[GSterbrant]

We don't seem to have that mentioned elsewhere in the docs, but we do set 'g' as the default channel in the material. It should be down to how textures are packed, surely, unless there is some bit depth favor for green channels (which would make sense perceptually) for certain file formats?

[Mistale]

I've added a clarification about the default value. I can't figure out why 'g' is the default for ao either, but I figured I'd just follow the same standard as aoMapChannel.
When packing ORM-textures for glTF, "r" is used for occlusion. But it may be related to inherent precision issues as @GSterbrant mentions.

[mvaligursky]

I'm approving this, with a small JSDocs suggestion, but would like @GSterbrant to have a look as well.

My question is regarding the aoDetailMode parameter - did you find this useful when testing, versus just using one fixed way to blend those ao maps?

[GSterbrant]

Looks good! Just remember to update the chunk API version to 1.63 before merge.

It does spawn a conversation I think we've had before on the team which is that perhaps we should add details maps as an intrinsic engine feature instead of having to add a bunch of extra parameters manually for each texture you'd want to detail map.

[GSterbrant]

We don't seem to have that mentioned elsewhere in the docs, but we do set 'g' as the default channel in the material. It should be down to how textures are packed, surely, unless there is some bit depth favor for green channels (which would make sense perceptually) for certain file formats?

[Mistale]

I'm approving this, with a small JSDocs suggestion, but would like @GSterbrant to have a look as well.

My question is regarding the aoDetailMode parameter - did you find this useful when testing, versus just using one fixed way to blend those ao maps?

I think that using DETAILMODE_MUL as default covers a lot of normal use-cases, with one specific exception:

• When multiplying primary and secondary AO together using mul, the results will always vary (slightly) by the pattern of the secondary map, even in areas where the primary occlusion should be dark enough to completely remove details.
  In this case a choice between DETAILMODE_MIN and DETAILMODE_MAX can make the results "flatter" while at the same time allowing the artist to introduce a bias towards the lighter or darker spectrum.

The other options are mainly there for artistic freedom.

[willeastcott]

This now has two approvals - any objections to merging @mvaligursky and @slimbuck? Last call for comments! ⌛

[mvaligursky]

Lets merge it in.