[x3d-public] Updated summary of my changes to X3Dv4, and reasoning "why do we need UnlitMaterial"

[GPU Group]

OK one more idea I haven't tried:
Could a browser loop on the CPU side, drawing the same object twice, once
with front material the front facing fragments, once with back material
drawing back facing fragments -different compiled shaders- and setting one
uniform or #define in the shader to say to draw front or back side of
fragments?
If so then that would simplify supporting front/back materials.
-Doug

On Mon, Mar 9, 2020 at 7:55 AM Michalis Kamburelis <michalis.kambi at gmail.com>
wrote:

> AD 1 - Yes, using backMaterial will require using containerField in X3D
> XML.
>
> AD 2 - The specification of backMaterial will deliberately contain
> wording to make implementation easier.
>
> Namely:
>
> - backMaterial can be <> NULL only if material <> NULL
>
> - when both material and backMaterial are <> NULL, they must indicate
> *the same* node class, IOW:
>
>     - they must both be Material
>     - or they must both be UnlitMaterial
>     - or they must both be PhysicalMaterial
>
> - moreover, when both material and backMaterial are <> NULL, they must
> have equal values for all xxxTexture and xxxTextureChannel fields.
> This means that the only difference can be in vector/scalar
> parameters. This means that e.g. you cannot use cubemap for
> diffuseTexture on front, and 3D texture for diffuseTexture on back.
>
>     (Browsers are of course free to "lift" this limitation and allow
> more. But I would prefer to keep the required functionality of it, in
> X3D 4.0, simple.)
>
> - Indeed we will add wording to prohibit placing TwoSidedMaterial in
> backMaterial :) Added to my TODO.
>
> - Note that the requirement to implement backMaterial will be rather
> high level of the appropriate component. I don't want to force all
> browsers to implement this. I doubt that CGE will actually implement
> it -- the use-cases for this are rather small, i.e. I never heard
> anyone ask me to support TwoSidedMaterial with separateBackColor=TRUE
> :)
>
> Regards,
> Michalis
>
> pon., 9 mar 2020 o 14:06 GPU Group <gpugroup at gmail.com> napisał(a):
> >
> > I'm enjoying - a big help to have clear targets even if changed, and
> I've been refactoring old code to prepare. Thanks very much Michalis, very
> helpful.
> > -Doug
> > ...
> > my experience so far:
> > I'm planning to put Physical and Unlit into normal workflow in freewrl,
> and fixing old bugs and bad code in preparation.
> > Some gotchas:
> > a)Appearance.backMaterial: freewrl x3d parser needs
> containerField='backMaterial' on one material, to work generically
> > <Appearance>
> > <Material ... />
> > <Material ... containerField='backMaterial'/>
> > </Appearance>
> > otherwise it seems to overwrite the material slot with the 2nd material
> > b) Appearance.backMaterial vs TwoSidedMaterial:
> > - TwoSided constrains to 2 'regular' materials
> > - Appearance.backside can sport new Unlit or Physical
> > - (gotcha: someone puts TwoSided in both material and.backMaterial )
> > So the shader workflow needs to support combinations of 2 material types
> at the same time and switch on something like gl_FrontFacing
> > (I need to refactor from #defines to uniforms for determining shader
> pathways, like we do with light types - ie FrontMaterial.type would
> indicate Unlit, Regular or Physical or None )
> >
> > On Sat, Mar 7, 2020 at 4:32 PM Michalis Kamburelis <
> michalis.kambi at gmail.com> wrote:
> >>
> >> Hi,
> >>
> >> 1. I have improved a "summary page" documenting my proposed changes for
> X3D v4:
> >>
> >>
> https://github.com/michaliskambi/x3d-tests/wiki/X3D-version-4:-New-features-of-materials,-lights-and-textures
> >>
> >> That page is designed to be a quick introduction to all the changes.
> >> It will also serve as a summary of my talk on next Friday (13th of
> >> March) on Web3D teleconference.
> >>
> >> 2. I wrote a dedicated page about "Why do we need UnlitMaterial
> >> node?". It's not so trivial question, and I gathered some arguments
> >> before I decided it's the right course of action. It's all documented
> >> on this page:
> >>
> >>
> https://github.com/michaliskambi/x3d-tests/wiki/Why-is-UnlitMaterial-useful
> >>
> >> Enjoy :),
> >> Michalis
> >>
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