[WIP] Implementation of PBR in glTF

[xtanion]

This PR needs a lot of cleaning and still in progress. As of now this PR adds ORM, Normal & Emissive materials. Most of the glTF models has been modified to use the ORM material, however few of them still use MetallicRoughness and AmbientOcclusion materials separately (for e.g. DamagedHelmet & Avocado).
Few model may have RoughnessMetallic instead of MetallicRoughness which changes switches the channels (For e.g. the Avocado model), as mentioned in this comment. This PR currently does not support the RoughnessMetallic.

Preview with the DamagedHelmet (has all three of materials) model:

Sample of the Avocado model (without switching the channels in RoughnessMetallic to MetallicRoughness) ( Left)
After switching channels (Right):

[Garyfallidis]

Very impressive !!! Emissive seems working very well.

[Garyfallidis]

Why the colors are so dark on the helmet? The correct rendering should look like this...

From the description above I am not sure where the issue is.

[Garyfallidis]

Above IBL is on. This is how it should look without IBL.

[Garyfallidis]

@xtanion this PR needs rebasing. We should resume the glft/pbr meeting too @guaje

[Garyfallidis]

@xtanion please resolve conflicts and let's move to the final steps of Gltf support. @guaje let's meet asap!

[xtanion]

Sorry for the late reply @Garyfallidis, my school examinations were going on. I'll fix this ASAP.

[Garyfallidis]

Ping @xtanion Let us know if you need a meeting to finalize this.

[Garyfallidis]

@xtanion please provide feedback asap.

[xtanion]

Sorry for the late response, I was traveling this entire week. I'll be working on this from Friday.

[skoudoro]

Sorry for the late response, I was traveling this entire week. I'll be working on this from Friday.

Great! Do you have any progress on this? if yes, can you push it?

thank you @xtanion.

ps: Also, it would be great if you could attend the fury open meeting this Thursday (March 30)

[skoudoro]

ping @xtanion

[Garyfallidis]

There are still some conflicts. Can you also list the remaining steps needed for this PR? @xtanion ?

[Garyfallidis]

@xtanion a reminder to move forward with this PR.