Compatibility of CESIUM_RTC and materials extensions

[lexaknyazev]

If a material doesn't have any technique because of materials extension use, where should parameter with "CESIUM_RTC_MODELVIEW" semantic be located?

[pjcozzi]

We haven't ran into this in practice, but we could, especially since Cesium supports both extensions. I feel like the solution will be when the materials extension is used to allow the material/technique to still list parameters to be merged with it. That could be messy though.

Perhaps table this until we have more cycles or there is community feedback to prioritize it, e.g., because it becomes a more broad problem with extension compatibility.

[lexaknyazev]

The issue is bigger than just CESIUM_RTC, since any extension could define new parameter semantics and therefore be incompatible with materials extensions. Something to think of for future cycles.

[lexaknyazev]

@pjcozzi Any updates on CESIUM_RTC with glTF 2.0?

[pjcozzi]

@lilleyse have we ran into this yet?

[lilleyse]

I'm not sure if we have, but there is a workaround in the code that if a glTF 2.0 model has the CESIUM_RTC extension (without techniques) the internal model view matrix applies the CESIUM_RTC value.

[emackey]

Seems like this is OBE.