Export Blender to Babylon.js fails

Question

I'm using Blender 4.0.2 and Blender2Babylon-3.3x.zip, that I downloaded from github repo here. I created new file with cube model and deleted camera and light, so there is nothing except cube.

During export I'm getting the next error:

bpy.ops.outliner.item_activate(deselect_all=True)
bpy.ops.outliner.delete()
bpy.ops.outliner.item_activate(deselect_all=True)
bpy.ops.outliner.delete()
bpy.context.space_data.system_bookmarks_active = 3
bpy.context.space_data.params.filename = "cube.babylon"
Python: Traceback (most recent call last):
  File "C:\Users\melas\AppData\Roaming\Blender Foundation\Blender\4.0\scripts\addons\babylon_js\json_exporter.py", line 118, in execute
    mesh = Mesh(object, scene, self)
  File "C:\Users\melas\AppData\Roaming\Blender Foundation\Blender\4.0\scripts\addons\babylon_js\mesh.py", line 151, in __init__
    recipe = BakingRecipe(bpyMesh, exporter)
  File "C:\Users\melas\AppData\Roaming\Blender Foundation\Blender\4.0\scripts\addons\babylon_js\materials\baking_recipe.py", line 43, in __init__
    bjsMaterial = BJSMaterial(bpyMaterial, exporter)
  File "C:\Users\melas\AppData\Roaming\Blender Foundation\Blender\4.0\scripts\addons\babylon_js\materials\material.py", line 109, in __init__
    self.bjsNodeTree = AbstractBJSNode.readMaterialNodeTree(bpyMaterial.node_tree, self.overloadChannels)
  File "C:\Users\melas\AppData\Roaming\Blender Foundation\Blender\4.0\scripts\addons\babylon_js\materials\nodes\abstract.py", line 265, in readMaterialNodeTree
    return AbstractBJSNode.readNodeTree(node_tree, 'ShaderNodeOutputMaterial', overloadChannels)
  File "C:\Users\melas\AppData\Roaming\Blender Foundation\Blender\4.0\scripts\addons\babylon_js\materials\nodes\abstract.py", line 285, in readNodeTree
    return AbstractBJSNode(output, topLevelId, overloadChannels)
  File "C:\Users\melas\AppData\Roaming\Blender Foundation\Blender\4.0\scripts\addons\babylon_js\materials\nodes\abstract.py", line 84, in __init__
    bjsWrapperNode = AbstractBJSNode.GetBJSWrapperNode(nodeSocket.links[0].from_node, nodeSocket.name, overloadChannels)
  File "C:\Users\melas\AppData\Roaming\Blender Foundation\Blender\4.0\scripts\addons\babylon_js\materials\nodes\abstract.py", line 335, in GetBJSWrapperNode
    return PrincipledBJSNode(bpyNode, socketName, overloadChannels)
  File "C:\Users\melas\AppData\Roaming\Blender Foundation\Blender\4.0\scripts\addons\babylon_js\materials\nodes\principled.py", line 25, in __init__
    subsurface = self.getDefault('Subsurface')
  File "C:\Users\melas\AppData\Roaming\Blender Foundation\Blender\4.0\scripts\addons\babylon_js\materials\nodes\abstract.py", line 217, in getDefault
    return self.defaults[socketName]
KeyError: 'Subsurface'

Answer 1

It doesn't look like Blender2Babylon supports Blender 4.0, the last commit to the repository was in September, before even the release of Blender 4.0. The actual issue you are facing could be due to the changes made to the Subsurface modifier in the Principled BSDF, as per the release notes "Subsurface scattering [now] uses the base color instead of a separate color input" which could be tripping Blender2Babylon up as it tries to save all the properties.

As for a solution here are some options:

• You could downgrade your Blender (not great but will probably work)
• It looks like https://forum.babylonjs.com/t/blender-4-0-pbr-mapping-for-exporter/47367 address the same issue and could offer a solution.
• You could also modify the addon itself to stop it from exporting the subsurface property (which does mean you won't be exporting that detail), the problematic code can be found under \Blender Foundation\Blender\4.0\scripts\addons\babylon_js\materials\nodes\principled.py line 25 to 31. You could basically just comment out the whole subsurface code (I've attached a screenshot showing the selected code to comment out).

As I don't use BabylonJS I haven't been able to test these out but it should at least narrow down what the issue is.