USD Preview Surface material export.

Add `USD Preview Surface From Nodes` export option, to convert a
Principled BSDF material node network to an approximate USD Preview
Surface shader representation. If this option is disabled, the original
material export behavior is maintained, where viewport setting are saved
to the Preview Surface shader.

Also added the following options for texture export.

  - `Export Textures`: If converting Preview Surface, export textures
    referenced by shader nodes to a 'textures' directory which is a
    sibling of the USD file.
  - `Overwrite Textures`: Allow overwriting existing texture files when
    exporting textures (this option is off by default).
  - `Relative Texture Paths`:  Make texture asset paths relative to the
    USD.

The entry point for the new functionality is
`create_usd_preview_surface_material()`, called from
`USDAbstractWriter::ensure_usd_material()`.  The material conversion
currently handles a small subset of Blender shading nodes,
`BSDF_DIFFUSE`, `BSDF_PRINCIPLED`, `TEX_IMAGE` and `UVMAP`.

Texture export is handled by copying texture files from their original
location to a `textures` folder in the same directory as the USD.
In-memory and packed textures are saved directly to the textures folder.

This patch is based, in part, on code in Tangent Animation's USD
exporter branch.

Reviewed By: sybren, HooglyBoogly

Differential Revision: https://developer.blender.org/D13647

1 files changed, 55 insertions, 0 deletions

diff --git a/source/blender/editors/io/io_usd.c b/source/blender/editors/io/io_usd.c
index 4e2ccea36ab..49d60ede277 100644
--- a/source/blender/editors/io/io_usd.c
+++ b/source/blender/editors/io/io_usd.c
@@ -131,6 +131,11 @@ static int wm_usd_export_exec(bContext *C, wmOperator *op)
   const bool use_instancing = RNA_boolean_get(op->ptr, "use_instancing");
   const bool evaluation_mode = RNA_enum_get(op->ptr, "evaluation_mode");
 
+  const bool generate_preview_surface = RNA_boolean_get(op->ptr, "generate_preview_surface");
+  const bool export_textures = RNA_boolean_get(op->ptr, "export_textures");
+  const bool overwrite_textures = RNA_boolean_get(op->ptr, "overwrite_textures");
+  const bool relative_texture_paths = RNA_boolean_get(op->ptr, "relative_texture_paths");
+
   struct USDExportParams params = {
       export_animation,
       export_hair,
@@ -141,6 +146,10 @@ static int wm_usd_export_exec(bContext *C, wmOperator *op)
       visible_objects_only,
       use_instancing,
       evaluation_mode,
+      generate_preview_surface,
+      export_textures,
+      overwrite_textures,
+      relative_texture_paths,
   };
 
   bool ok = USD_export(C, filename, &params, as_background_job);
@@ -173,6 +182,26 @@ static void wm_usd_export_draw(bContext *UNUSED(C), wmOperator *op)
   uiItemR(col, ptr, "evaluation_mode", 0, NULL, ICON_NONE);
 
   box = uiLayoutBox(layout);
+  col = uiLayoutColumnWithHeading(box, true, IFACE_("Materials"));
+  uiItemR(col, ptr, "generate_preview_surface", 0, NULL, ICON_NONE);
+  const bool export_mtl = RNA_boolean_get(ptr, "export_materials");
+  uiLayoutSetActive(col, export_mtl);
+
+  uiLayout *row = uiLayoutRow(col, true);
+  uiItemR(row, ptr, "export_textures", 0, NULL, ICON_NONE);
+  const bool preview = RNA_boolean_get(ptr, "generate_preview_surface");
+  uiLayoutSetActive(row, export_mtl && preview);
+
+  row = uiLayoutRow(col, true);
+  uiItemR(row, ptr, "overwrite_textures", 0, NULL, ICON_NONE);
+  const bool export_tex = RNA_boolean_get(ptr, "export_textures");
+  uiLayoutSetActive(row, export_mtl && preview && export_tex);
+
+  row = uiLayoutRow(col, true);
+  uiItemR(row, ptr, "relative_texture_paths", 0, NULL, ICON_NONE);
+  uiLayoutSetActive(row, export_mtl && preview);
+
+  box = uiLayoutBox(layout);
   uiItemL(box, IFACE_("Experimental"), ICON_NONE);
   uiItemR(box, ptr, "use_instancing", 0, NULL, ICON_NONE);
 }
@@ -249,6 +278,32 @@ void WM_OT_usd_export(struct wmOperatorType *ot)
                "Use Settings for",
                "Determines visibility of objects, modifier settings, and other areas where there "
                "are different settings for viewport and rendering");
+
+  RNA_def_boolean(ot->srna,
+                  "generate_preview_surface",
+                  true,
+                  "To USD Preview Surface",
+                  "Generate an approximate USD Preview Surface shader "
+                  "representation of a Principled BSDF node network");
+
+  RNA_def_boolean(ot->srna,
+                  "export_textures",
+                  true,
+                  "Export Textures",
+                  "If exporting materials, export textures referenced by material nodes "
+                  "to a 'textures' directory in the same directory as the USD file");
+
+  RNA_def_boolean(ot->srna,
+                  "overwrite_textures",
+                  false,
+                  "Overwrite Textures",
+                  "Allow overwriting existing texture files when exporting textures");
+
+  RNA_def_boolean(ot->srna,
+                  "relative_texture_paths",
+                  true,
+                  "Relative Texture Paths",
+                  "Make texture asset paths relative to the USD file");
 }
 
 /* ====== USD Import ====== */