Add emission_weight

[portsmouth]

Implements the change described in #229.

[ZapAndersson]

I approve.

[portsmouth]

emission_weight luminance emission_luminance needs to default to 1000 in both the text and the parametrization table.

[virtualzavie]

emission_weight luminance needs to default to 1000 in both the text and the parametrization table.

Ah right, I see the parameter list still has a luminance default value of 0 (assuming you meant emission_luminance, not emission_weight).
If we have two parameters, indeed, one of them must have a default value different from 0.

The default value 1000 sounds reasonable to me since it's the order of magnitude of the maximum luminance of typical displays screens (smartphones and TVs).

[jstone-lucasfilm]

This looks fine to me, though it would be ideal to update the reference implementation in sync with this change, so that we don't accidentally create divergence between them.

[portsmouth]

This looks fine to me, though it would be ideal to update the reference implementation in sync with this change, so that we don't accidentally create divergence between them.

Done in eed5022

[portsmouth]

@jstone-lucasfilm can be merged?

[jstone-lucasfilm]

@portsmouth This looks very close to the mark, but we should update Anton's open_pbr_lightbulb.mtlx example so that it remains an emissive material in OpenPBR 1.2!

https://github.com/AcademySoftwareFoundation/OpenPBR/blob/main/examples/open_pbr_lightbulb.mtlx

[portsmouth]

@portsmouth This looks very close to the mark, but we should update Anton's open_pbr_lightbulb.mtlx example so that it remains an emissive material in OpenPBR 1.2!

https://github.com/AcademySoftwareFoundation/OpenPBR/blob/main/examples/open_pbr_lightbulb.mtlx

Done in 203103e. Hopefully there aren't a lot of existing assets out there that will be bitten by this (I assume not, yet..).

[jstone-lucasfilm]

This looks good to me, thanks @portsmouth!