lib+blender: Various fixes to make material converting more robust

On the lib side, I detect and emit a warning if a shader buffer is empty
(which shouldn't happen, but can if the API is used 'incorrectly').
I also patch in a null material to make the renderer happy, since it
assumes that there is at least one material there.
On the blender side, I now convert the material trees once, instead of
repeating the conversion for every mesh, since meshes often share
materials.

bindings/blender_init.py

@@ -184,6 +184,11 @@ def sync_scene(self, renderer, depsgraph, b_scene):
 				else:
 					cr_cam.set_param(c_ray.cam_param.focus_distance, bl_cam.dof.focus_distance)
 
+		cr_materials = {}
+		for bl_mat in bpy.data.materials:
+			print("Converting {}".format(bl_mat.name))
+			cr_materials[bl_mat.name] = convert_node_tree(depsgraph, bl_mat, bl_mat.node_tree)
+
 		# Sync meshes
 		for idx, ob_main in enumerate(objects):
 			if ob_main.type != 'MESH':
@@ -209,12 +214,15 @@ def sync_scene(self, renderer, depsgraph, b_scene):
 				continue
 			# FIXME: Parse & convert these to an array before parsing meshes, then pick from there
 			# We're doing duplicate work for many materials
+			if len(me.materials) < 1:
+				cr_mat_set.add(None)
 			for bl_mat in me.materials:
 				if not bl_mat:
 					print("WTF, array contains NoneType?")
+					cr_mat_set.add(None)
 				elif bl_mat.use_nodes:
-					print("Converting material {}".format(bl_mat.name))
-					cr_mat_set.add(convert_node_tree(depsgraph, bl_mat, bl_mat.node_tree))
+					print("Fetching material {}".format(bl_mat.name))
+					cr_mat_set.add(cr_materials[bl_mat.name])
 				else:
 					print("Material {} doesn't use nodes, do something about that".format(bl_mat.name))
 					cr_mat_set.add(None)

bindings/nodes/convert.py

@@ -25,6 +25,9 @@ def convert_background(nt):
 
 
 def convert_node_tree(bl_depsgraph, mat, nt):
+	if not nt:
+		print("No node tree in material {}, bailing out".format(mat.name))
+		return None
 	if len(nt.nodes) < 1:
 		print("No nodes found for material {}, bailing out".format(mat.name))
 		return None

src/lib/renderer/renderer.c

@@ -150,6 +150,12 @@ struct cr_bitmap *renderer_render(struct renderer *r) {
 
 	struct tile_set set = tile_quantize(camera.width, camera.height, r->prefs.tileWidth, r->prefs.tileHeight, r->prefs.tileOrder);
 
+	for (size_t i = 0; i < r->scene->shader_buffers.count; ++i) {
+		if (!r->scene->shader_buffers.items[i].bsdfs.count) {
+			logr(warning, "bsdf buffer %zu is empty, patching in placeholder\n", i);
+			bsdf_node_ptr_arr_add(&r->scene->shader_buffers.items[i].bsdfs, build_bsdf_node((struct cr_scene *)r->scene, NULL));
+		}
+	}
 	// Bind object buffers to instances
 	for (size_t i = 0; i < r->scene->instances.count; ++i) {
 		struct instance *inst = &r->scene->instances.items[i];