Update on multi-channel texture_info and 3-channel texcoord bindings.

extensions/2.0/Khronos/KHR_texture_procedurals/README.md

@@ -442,6 +442,8 @@ Semantics for texture coordinate lookups are as follows:
 
 1. The current [specification language for meshes]((https://registry.khronos.org/glTF/specs/2.0/glTF-2.0.html#meshes-overview)) notes that texture coordinates are 
 2 channel. In order to support 3D texture coordinates it is proposed that the semantics of this binding be extended to allow 3 channel texture coordinates.
+This is currently beyond the scope of this extension, thus validation for
+for this version will consider these nodes as being invalid.
 
 2. Texture coordinates may be routed in a graph through one or more downstream nodes which may perform a mathematical operation on the coordinates. To avoid ambiguity any transform specified on a texture should be ignored / removed. 
 

extensions/2.0/Vendor/EXT_texture_procedurals_mx_1_39/README.md

@@ -79,17 +79,19 @@ The `procedurals` array specifies the procedural graphs for a given set of nodes
 
 ## Handling MaterialX glTF PBR Nodes
 
-The glTF PBR node specified within MaterialX exposes a number of input ports which may not map 1:1 with the glTF PBR material
-for texture mapping. That is `texture_info` mappings in glTF PBR may not map directly to the input ports of the MaterialX PBR node.
+The glTF PBR node specified within MaterialX exposes a number of input ports which may not map 1:1 with the glTF PBR material for texture mapping. That is, `texture_info` mappings in glTF PBR may not map directly to the input ports of the MaterialX PBR node.
 
-One example is the mismatch of `metalicRoughnessTexture` which is a single packed 3 or 4  channel image which is minimally split into two input ports `metallic` and `roughness` on a glTF PBR shader in MaterialX. ( It is to be determined what it means to have different upstream connections for each port when mapping to a single `texture_info`).
+One example is the mismatch of `metalicRoughnessTexture` which is a single packed 3 or 4  channel image which is minimally split into two input ports `metallic` and `roughness` on a glTF PBR shader in MaterialX.
 
 Below is the Boombox glTF example as expressed in MaterialX. The top image shows the mapping to the shader port connects and the bottom a subgraph which shows how an ORM image is split to the `metallic` and `roughness` and `occlusion` ports.
 
 <img src="figures/boombox_mapping.png" width=60%>
 <img src="figures/boombox_mapping2.png" width=60%>
 
-Any channels mapped on the MaterialX glTF PBR node which do not correspond to a `texture_info` mapping should be ignored or pre-processed to an appropriate scalar value. 
+Any channels mapped on the MaterialX glTF PBR node which do not correspond to a `texture_info` mapping should be ignored as being invalid or pre-processed to insert the appropriate node within the procedural graph to combine the outputs so that they are mappable. For the example, a `combine` node has been added. The 
+split outputs can be reconstituted when converted back (e.g. to MaterialX) for an integration which uses separated inputs.
+
+<img src="figures/combine_channels.png" width=60%>
 
 ## JSON Schema