Refresh generated terrain assets and projection

tools/blender/export_terrain_chunks.py

@@ -10,10 +10,11 @@ Run through Blender rather than a standalone Python interpreter:
 Collections use ``chunk_####_description`` and contain one primary terrain
 mesh named ``chunk_####``. Additional production objects may live in the same
 collection. Reusable procedural props use individual ``prop_description``
-mesh objects. They may be arranged anywhere in the source file because each
-object's authored origin becomes the exported runtime anchor. A same-named
-``prop_description`` collection remains supported for multi-object props.
-Unrelated objects and collections are ignored.
+mesh objects. Their child empties are exported with them so authored sockets
+remain attached to the prop. Props may be arranged anywhere in the source file
+because each root object's authored origin becomes the exported runtime anchor.
+A same-named ``prop_description`` collection remains supported for multi-object
+props. Unrelated objects and collections are ignored.
 """
 
 from __future__ import annotations
@@ -43,6 +44,12 @@ PROP_COLLECTION_PATTERN = re.compile(
     r"^prop_(?P<label>[a-z0-9]+(?:_[a-z0-9]+)*)$"
 )
 ALLOWED_OBJECT_TYPES = {"EMPTY", "MESH"}
+UPWARD_SURFACE_MATERIALS = {
+    "dirt",
+    "grass_lite",
+    "sand",
+    "water_reference",
+}
 
 
 class ExportValidationError(RuntimeError):
@@ -167,6 +174,33 @@ def _validate_transform(
     return problems
 
 
+def _validate_upward_surface_normals(
+    mesh_object: bpy.types.Object,
+) -> list[str]:
+    """Reject exposed terrain materials whose faces point into the ground."""
+    downward_counts: dict[str, int] = {}
+    materials = mesh_object.data.materials
+    for polygon in mesh_object.data.polygons:
+        if polygon.normal.z >= -0.25 or polygon.material_index >= len(materials):
+            continue
+        material = materials[polygon.material_index]
+        if material is None:
+            continue
+        material_name = re.sub(r"\.\d{3}$", "", material.name)
+        if material_name not in UPWARD_SURFACE_MATERIALS:
+            continue
+        downward_counts[material_name] = (
+            downward_counts.get(material_name, 0) + 1
+        )
+    return [
+        (
+            f"{count} {material_name} face(s) point downward; "
+            "terrain surface normals must face up"
+        )
+        for material_name, count in sorted(downward_counts.items())
+    ]
+
+
 def _validate_bounds(
     bounds: Bounds,
     tolerance: float,
@@ -318,6 +352,10 @@ def _discover_chunks(tolerance: float) -> list[ChunkSource]:
             errors.append(
                 f"{collection.name}/{primary_mesh.name}: mesh has no material"
             )
+        errors.extend(
+            f"{collection.name}/{primary_mesh.name}: {problem}"
+            for problem in _validate_upward_surface_normals(primary_mesh)
+        )
 
         chunks.append(
             ChunkSource(
@@ -522,20 +560,38 @@ def _discover_props(tolerance: float) -> list[PropSource]:
         if not collections:
             errors.append(f"{item.name}: prop object belongs to no collection")
             continue
+        objects = tuple(
+            sorted(
+                (item, *item.children_recursive),
+                key=lambda value: value.name,
+            )
+        )
+        overlapping_sources = {
+            claimed_objects[descendant.as_pointer()]
+            for descendant in objects
+            if descendant.as_pointer() in claimed_objects
+        }
+        if overlapping_sources:
+            errors.append(
+                f"{item.name}: child object is already exported by "
+                f"{', '.join(sorted(overlapping_sources))}"
+            )
+            continue
         prop, source_errors = _make_prop_source(
             stable_id,
             match.group("label"),
             "object",
             item.name,
             collections[0],
-            (item,),
+            objects,
             tolerance,
         )
         errors.extend(source_errors)
         if prop is not None:
             props.append(prop)
             claimed_ids[stable_id] = item.name
-            claimed_objects[item.as_pointer()] = item.name
+            for descendant in objects:
+                claimed_objects[descendant.as_pointer()] = item.name
 
     if errors:
         raise ExportValidationError("\n".join(errors))