GLTF loader improvements

[TheMostDiligent]

• GLTF Loader: support multiple Scenes #193
• Multiple animations at the same time + Fox
  • Requires changes to ComputeTransforms
• Morph Targets
• Vertex Colors Can't support gltf model with vertex color DiligentEngine#58
  • If ModelCI.VertexAttributes == null, let the loader automatically define the layout based on the attributes available in the model
  • Change the renderer to support various input attribute combinations
  • Alternatively, have dummy input buffers (e.g. vertex colors) with Stride 0
• Metal Rough Textureless
• Rework loader to load all nodes, meshes and cameras and allow selecting the scene to render at run time
• Attenuation
  • 5d1dea2
• Clearcoat
  • 2c436c4
• Emissive Strength
  • 28cf257
  • DiligentGraphics/DiligentFX@3163b3f
• Iridescence
  • a464d01
• Transmission
  • a6e8a4b
• Unlit
  • e2feb7e
  • DiligentGraphics/DiligentFX@11a6cd8
• Punctual Lights
  • LightsPunctualLamp
  • da116e3

[Alan-FGR]

I've a quick question: I see you have "Multiple animations at the same time" unticked there which is blocked by the current impl of ComputeTransforms, but isn't it currently possible to manually "blend" two animations without that feature? If you have two animations for the same bones, isn't it trivial to interpolate between them for transitions and whatnot?

[TheMostDiligent]

@Alan-FGR You might be right. You can have multiple transform instances for different animations.
As far as I remember, the idea was to have different animations in the same struct to avoid duplicating the data. For example, in this test scene, different meshes are animated with different animations. It is possible to do this now, but this would require creating multiple transform instances.