From 63f2a2ab4e13392b3add0cefcb65c193451ee4d3 Mon Sep 17 00:00:00 2001
From: Mikko Rasa <tdb@tdb.fi>
Date: Sat, 13 Feb 2021 20:53:41 +0200
Subject: [PATCH] Support exporting "empty" materials with only a technique or
 shader

---
 blender/io_mspgl/export_material.py | 13 ++++++++++---
 blender/io_mspgl/material.py        |  7 ++++++-
 2 files changed, 16 insertions(+), 4 deletions(-)

diff --git a/blender/io_mspgl/export_material.py b/blender/io_mspgl/export_material.py
index 2df04ff6..266790f2 100644
--- a/blender/io_mspgl/export_material.py
+++ b/blender/io_mspgl/export_material.py
@@ -7,7 +7,8 @@ def create_technique_resource(material, resources):
 	mat_res = resources[material.name+".mat"]
 
 	st = Statement("pass", "")
-	st.sub.append(tech_res.create_embed_statement("material", mat_res))
+	if mat_res:
+		st.sub.append(tech_res.create_embed_statement("material", mat_res))
 
 	if material.render_mode=='CUSTOM':
 		st.sub.append(Statement("shader", material.shader))
@@ -48,7 +49,10 @@ class MaterialExporter:
 
 		mat_name = material.name+".mat"
 		if mat_name not in resources:
-			resources[mat_name] = self.export_material(material, resources=resources)
+			if material.type:
+				resources[mat_name] = self.export_material(material, resources=resources)
+			else:
+				resources[mat_name] = None
 
 	def export_technique(self, material, *, resources):
 		return create_technique_resource(material, resources)
@@ -57,7 +61,10 @@ class MaterialExporter:
 		from .datafile import Resource, Statement
 		mat_res = Resource(material.name+".mat", "material")
 
-		st = Statement("pbr")
+		if material.type!="pbr":
+			raise Exception("Can't export unknown material type "+material.type)
+
+		st = Statement(material.type)
 		for kw, p in material.properties.items():
 			ss = self.create_property_statement(mat_res, p, kw, resources)
 			if ss:
diff --git a/blender/io_mspgl/material.py b/blender/io_mspgl/material.py
index e8a9089a..3b790361 100644
--- a/blender/io_mspgl/material.py
+++ b/blender/io_mspgl/material.py
@@ -48,6 +48,7 @@ class MaterialProperty:
 class Material:
 	def __init__(self, material):
 		self.name = material.name
+		self.type = None
 		self.properties = {}
 
 		self.render_mode = material.render_mode
@@ -70,10 +71,14 @@ class Material:
 
 		surface_node, _ = get_linked_node_and_socket(material.node_tree, out_node.inputs["Surface"])
 		if not surface_node:
-			raise Exception("Material has no surface node")
+			if self.render_mode=='BUILTIN':
+				raise Exception("Empty material can't use builtin rendering mode")
+			return
 		elif surface_node.type!='BSDF_PRINCIPLED':
 			raise Exception("Unsupported surface node type "+surface_node.type)
 
+		self.type = "pbr"
+
 		base_color = self.properties["base_color"] = MaterialProperty((0.8, 0.8, 0.8, 1.0))
 		metalness = self.properties["metalness"] = MaterialProperty(0.0)
 		roughness = self.properties["roughness"] = MaterialProperty(0.5)
-- 
2.45.2