From 8f6a13aa8fbb2f4dd1c3e133b17c5cdb96ba87d8 Mon Sep 17 00:00:00 2001
From: Robin Alazard <robinalazard@google.com>
Date: Fri, 27 Jun 2025 02:15:47 -0700
Subject: [PATCH] Add support for displayColor/Opacity (convert to rgba)

PiperOrigin-RevId: 776488857
Change-Id: I34713748ac553b5fdfad736801cdaa7dc2b7f1b0
---
 src/experimental/usd/usd_to_mjspec.cc | 28 +++++++++++++++++++++++++++
 1 file changed, 28 insertions(+)

diff --git a/src/experimental/usd/usd_to_mjspec.cc b/src/experimental/usd/usd_to_mjspec.cc
index 0e9e5ebf..d1c48ceb 100644
--- a/src/experimental/usd/usd_to_mjspec.cc
+++ b/src/experimental/usd/usd_to_mjspec.cc
@@ -49,6 +49,8 @@
 #include <pxr/usd/usdGeom/gprim.h>
 #include <pxr/usd/usdGeom/mesh.h>
 #include <pxr/usd/usdGeom/plane.h>
+#include <pxr/usd/usdGeom/primvar.h>
+#include <pxr/usd/usdGeom/primvarsAPI.h>
 #include <pxr/usd/usdGeom/sphere.h>
 #include <pxr/usd/usdGeom/tokens.h>
 #include <pxr/usd/usdGeom/xformCache.h>
@@ -742,6 +744,32 @@ void ParseUsdPhysicsCollider(mjSpec* spec,
     ParseMjcPhysicsCollisionAPI(geom, pxr::MjcPhysicsCollisionAPI(prim));
   }
 
+  // Convert displayColor and displayOpacity to rgba.
+  // We want to support primvar inheritance, hence FindPrimvarWithInheritance.
+  pxr::UsdGeomPrimvarsAPI primvarsAPI(prim);
+  pxr::UsdGeomPrimvar displayColorPrimvar =
+      primvarsAPI.FindPrimvarWithInheritance(
+          pxr::UsdGeomTokens->primvarsDisplayColor);
+  pxr::UsdGeomPrimvar displayOpacityPrimvar =
+      primvarsAPI.FindPrimvarWithInheritance(
+          pxr::UsdGeomTokens->primvarsDisplayOpacity);
+  if (displayColorPrimvar.HasAuthoredValue()) {
+    pxr::VtArray<pxr::GfVec3f> display_color;
+    displayColorPrimvar.Get(&display_color);
+    if (!display_color.empty()) {
+      geom->rgba[0] = display_color[0][0];
+      geom->rgba[1] = display_color[0][1];
+      geom->rgba[2] = display_color[0][2];
+    }
+  }
+  if (displayOpacityPrimvar.HasAuthoredValue()) {
+    pxr::VtArray<float> display_opacity;
+    displayOpacityPrimvar.Get(&display_opacity);
+    if (!display_opacity.empty()) {
+      geom->rgba[3] = display_opacity[0];
+    }
+  }
+
   SetLocalPoseFromPrim(prim, parent_prim, geom, xform_cache);
 
   if (!MaybeParseGeomPrimitive(prim, geom, xform_cache)) {