[Bf-blender-cvs] [176f8947cd5] sybren-usd: USD: Write mesh single/doublesidedness

[Sybren A. Stüvel]

Commit: 176f8947cd50f6a472dce67451b201bf74ae6dc1
Author: Sybren A. Stüvel
Date:   Fri Jul 12 12:22:15 2019 +0200
Branches: sybren-usd
https://developer.blender.org/rB176f8947cd50f6a472dce67451b201bf74ae6dc1

USD: Write mesh single/doublesidedness

USD seems to support neither per-material nor per-face-group
double-sidedness, so we just use the flag from the first non-empty
material slot. If there is no material we default to double-sidedness.

===================================================================

M	source/blender/usd/intern/usd_writer_mesh.cc

===================================================================

diff --git a/source/blender/usd/intern/usd_writer_mesh.cc b/source/blender/usd/intern/usd_writer_mesh.cc
index 7ce3102d864..14b5761ead9 100644
--- a/source/blender/usd/intern/usd_writer_mesh.cc
+++ b/source/blender/usd/intern/usd_writer_mesh.cc
@@ -192,10 +192,21 @@ void USDGenericMeshWriter::assign_materials(
 
     pxr::UsdShadeMaterial usd_material = ensure_usd_material(material);
     usd_material.Bind(usd_mesh.GetPrim());
+
+    /* USD seems to support neither per-material nor per-face-group double-sidedness, so we just
+     * use the flag from the first non-empty material slot. */
+    usd_mesh.CreateDoubleSidedAttr(
+        pxr::VtValue((material->blend_flag & MA_BL_CULL_BACKFACE) == 0));
+
     mesh_material_bound = true;
     break;
   }
 
+  if (!mesh_material_bound) {
+    /* Blender defaults to double-sided, but USD to single-sided. */
+    usd_mesh.CreateDoubleSidedAttr(pxr::VtValue(true));
+  }
+
   if (!mesh_material_bound || usd_face_groups.size() < 2) {
     /* Either all material slots were empty or there is only one material in use. As geometry
      * subsets are only written when actually used to assign a material, and the mesh already has