Support for glTF 2.0

[pjcozzi]

Changes from 1.0 to 2.0 are here: KhronosGroup/glTF#605

The 2.0 spec still needs a bit more work, but is converging quickly.

---

Cesium / glTF Pipeline / COLLADA2GLTF / 3D Tiles updates

• Add glTF 2.0 support (and still 1.0) to Cesium. Start with Marco's sample models if gltf-pipeline can't generate 2.0 models yet. Gltf 2.0 #4808
  • scene isn't required, The glTF.scene should be optional #4793
• Finish Update version gltf-pipeline#191 enough (if it isn't already) to regenerate all the required demo/test models for Cesium.
• Update the glTF Sample Models to 2.0 using gltf-pipeline. Resolve all of the outstanding PRs in this repo. Added generated 2.0 sample models KhronosGroup/glTF-Sample-Models#28
• Finish updating COLLADA2GLTF to 2.0. glTF 2.0 KhronosGroup/COLLADA2GLTF#20
• Update wetzel to v4 schema and regenerate property reference, glTF 2.0 draft KhronosGroup/glTF#826
• Any other gltf-pipeline changes (perhaps tests or doc) needed to merge, Added remove techniques stage gltf-pipeline#19.
• Separate gltf-pipeline pull request to use 2.0 internally for each stage. (part of the gltf-pipeline changes above)
• Update obj2gltf to 2.0, @lilleyse?
• Update model inspector to 2.0 (the UI might need some updates for the JSON changes, I dunno). It should still support 1.0 and convert to 2.0 on-the-fly like Cesium.
• Load Sketchfab models
• Morph targets / skinning fix: Mixing morph targets in materials crashes for glTF 2.0 models #5695
• Support for multiple animations with different end times: Multiple animations in a glTF 2.0 model causes an error #5694
• Render Polly model perfectly
• Sparse accessor support
• Spec-gloss extension, Provide a super simple way for engines to add support for spec gloss gltf-pipeline#331
  • Important since Sketchfab, Minecraft, and others export this
• Test Cesium with glTF-Asset-Generator, https://github.com/bghgary/glTF-Asset-Generator/issues/63
• glTF 2.0 images in buffers aren't mipmapped glTF 2.0 images in buffers aren't mipmapped #5905
• CubeMapGen could be useful if/when we implement IBL

TBA

• [ ] Update Cesium, gltf-pipeline, obj2gltf, COLLADA2GLTF, and sample models to use final version of KHR_materials_common, see Finishing KHR_materials_common KhronosGroup/glTF#632.
• Update the 3D Tiles b3dm/i3dm specs to reference 2.0, Reference glTF 2.0 spec 3d-tiles#94. Add a warning to Cesium if a tileset contains glTF 1.0.
• Update 3D Tiles tilesets in the 3d-tiles branch to 2.0.
• Update tiles in 3d-tiles-samples to 2.0.
• Update 3d-tiles-tools to 2.0.
  • createGltf.js

[lasalvavida]

Copying from #605 to track progress in Cesium.

• asset is now required (This shouldn't change anything in Cesium)
• accessor.min and accessor.max are now required, and clarified that the JSON value and binary data must be the same (This shouldn't change anything in Cesium)
• Added accessor.normalized (glTF 1.0.1 Adds support for normalized vertex arrays and a test #4247)
• buffer.byteLength and bufferView.byteLength are now required (This shouldn't change anything in Cesium)
• buffer.type can no longer be "text", which was not used (This shouldn't change anything in Cesium, we never supported that anyway)
• skin.inverseBindMatrices is now optional
• Attribute parameters can't have a value defined in the technique or parameter
• Only TEXCOORD and COLOR attribute semantics can be written in the form [semantic]_[set_index] (This shouldn't change anything in Cesium)
• TEXCOORD and COLOR attribute semantics must be written in the form [semantic]_[set_index], e.g., just TEXCOORD should be TEXCOORD_0, and just COLOR should be COLOR_0 (This shouldn't change anything in Cesium)
• camera.perspective.aspectRatio and camera.perspective.yfov must now be > 0, not >= 0 (This shouldn't change anything in Cesium, since we don't support glTF cameras)
• Application-specific parameter semantics must start with an underscore, e.g., _TEMPERATURE and _SIMULATION_TIME (This shouldn't change anything in Cesium)
• Added glExtensionsUsed property and 5125 (UNSIGNED_INT) accessor.componentType value (glTF 1.0.1 uint32 indices #4249)
• Properties in technique.parameters must be defined in technique.uniforms or technique.attributes,
• technique.parameter.count can only be defined when the semantic is JOINTMATRIX or an application-specific semantic is used. It can never be defined for attribute parameters; only uniforms
• technique.parameter.semantic is required when the parameter is an attribute
• material.parameter.value and technique.parameter.value must be an array
• Mesh-only models are allowed, e.g., without materials (glTF 1.0.1 default material #4251)
• Skeleton hierarchies (nodes containing jointName) must be separated from non-skeleton hierarchies.
• Removed technique.functions.scissor and removed 3089 (SCISSOR_TEST) as a valid value for technique.states.enable (glTF 1.0.1 remove scissor test #4248)

[lasalvavida]

@pjcozzi Do we want to completely pull support from SCISSOR_TEST throughout, or just when loading from a model?

[pjcozzi]

@pjcozzi Do we want to completely pull support from SCISSOR_TEST throughout, or just when loading from a model?

Remove it completely from glTF since it was never used, but do not remove it from the lower-level Cesium renderer.

[pjcozzi]

1.1 spec pull request: KhronosGroup/glTF#784

[cx20]

I tested the display of the tutorial model of glTF 1.1 with Cesium 1.29.
Some glTF 1.1 models can not be displayed, please confirm.
https://github.com/cx20/gltf-test#gltf-11-tutorial-models

An error occurred while rendering. Rendering has stopped.
TypeError: Cannot read property 'nodes' of undefined
TypeError: Cannot read property 'nodes' of undefined
    at ye (https://cx20.github.io/gltf-test/libs/cesium/1.29/Cesium.js:453:20512)
    at de.update (https://cx20.github.io/gltf-test/libs/cesium/1.29/Cesium.js:454:27770)
    at a.update (https://cx20.github.io/gltf-test/libs/cesium/1.29/Cesium.js:469:14800)
    at Ue (https://cx20.github.io/gltf-test/libs/cesium/1.29/Cesium.js:472:20935)
    at Ve (https://cx20.github.io/gltf-test/libs/cesium/1.29/Cesium.js:472:19556)
    at Be (https://cx20.github.io/gltf-test/libs/cesium/1.29/Cesium.js:472:17516)
    at qe (https://cx20.github.io/gltf-test/libs/cesium/1.29/Cesium.js:472:23594)
    at de.render (https://cx20.github.io/gltf-test/libs/cesium/1.29/Cesium.js:472:28774)
    at P.render (https://cx20.github.io/gltf-test/libs/cesium/1.29/Cesium.js:478:9308)
    at t (https://cx20.github.io/gltf-test/libs/cesium/1.29/Cesium.js:477:29290)

[lasalvavida]

Thanks @cx20. glTF 1.1 support is not integrated into mainline Cesium yet

[cx20]

I confirmed that the model of glTF 2.0 will be displayed by Cesium 1.36 (not 1.35).
https://github.com/cx20/gltf-test/tree/2.0

[pjcozzi]

@cx20 very nice, thanks for checking so quickly (also, I think you mean 1.36)!

[pjcozzi]

gltf-pipeline roadmap for glTF 2.0 - CesiumGS/gltf-pipeline#330

[pjcozzi]

@lilleyse can you please update the above tasklist? Some of the items are finished.

[pjcozzi]

@lilleyse can you please update the tasklists in this issue? What's left?

[lilleyse]

Updated the task list. The major things left are:

• Sparse accessors
• Spec gloss extension
• Update 3d-tiles samples and projects to use 2.0 (in progress)

[emackey]

• Support multiple (or at least two) UV maps (test model).
• Generate missing normals (Generate normals automatically for glTF 2.0 models #6506) per spec as flat-shaded instead of unlit.

[pjcozzi]

@ggetz could you please update the tasklists above? Perhaps we can close this and submit/update other issues.

[tkazik]

I guess this can safely be closed since a while :)
Thanks for all your efforts!