Refactor Cesium material export contract

blender/osmassets/materials.py

@@ -6,11 +6,14 @@ the catalog importable by plain Python, and by anything else that wants to read
 the scene's material definitions without launching Blender.
 """
 
+import json
 import os
 
 import bpy
 
 
+CESIUM_EXPORT_PROPERTY = "cesium_export"
+
 TEXTURE_ROOT = os.path.abspath(os.path.join(
     os.path.dirname(os.path.abspath(__file__)), "..", "..",
     "assets", "textures", "polyhaven"
@@ -195,15 +198,26 @@ def link_alpha_clip(material, alpha_output, bsdf, cutoff=0.5):
     material.use_backface_culling = False
 
 
+def apply_cesium_contract(material, spec):
+    contract = spec.get("cesium")
+    if contract is None:
+        if CESIUM_EXPORT_PROPERTY in material:
+            del material[CESIUM_EXPORT_PROPERTY]
+        return material
+    material[CESIUM_EXPORT_PROPERTY] = json.dumps(contract, sort_keys=True)
+    return material
+
+
 def from_spec(spec):
     """Build a material from a `catalog.MATERIALS` entry."""
     if spec["kind"] == "textured":
-        return make_textured_material(
+        material = make_textured_material(
             spec["name"], spec["diffuse"], spec["normal"],
             roughness=spec.get("roughness", 0.8), scale=spec["scale"],
             normal_is_bump=spec.get("normal_is_bump", False),
             metallic=spec.get("metallic", 0.0),
             tint=spec.get("tint"), tint_factor=spec.get("tint_factor", 0.0))
+        return apply_cesium_contract(material, spec)
 
     material = make_material(spec["name"], spec["color"],
                              spec.get("roughness", 0.8),
@@ -215,4 +229,4 @@ def from_spec(spec):
                                detail=procedural["detail"],
                                bump_strength=procedural["bump_strength"],
                                object_space=procedural.get("object_space", False))
-    return material
+    return apply_cesium_contract(material, spec)