From 6e915055577c2d931b51e9fd025f193c3f58bbb3 Mon Sep 17 00:00:00 2001
From: cpichard <cpichard@users.noreply.github.com>
Date: Tue, 11 Jun 2024 14:15:03 +0100
Subject: [PATCH] check if the VtValue is empty before doing a UncheckedGet
 (#1934)

---
 CHANGELOG.md                  |  1 +
 libs/render_delegate/mesh.cpp | 14 ++++++++------
 2 files changed, 9 insertions(+), 6 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index bcc8c707c..608cbe231 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -7,6 +7,7 @@
 - [usd#1923](https://github.com/Autodesk/arnold-usd/issues/1923) - Fix instance primvar indices 
 with multiple prototypes
 - [usd#1929](https://github.com/Autodesk/arnold-usd/issues/1929) - Ensure subdiv_iterations is not set uselessly during procedural updates
+- [usd#1932](https://github.com/Autodesk/arnold-usd/issues/1932) - Fix a crash when the number of elements in a primvar should be equal to the number of points but is not.
 
 ## [7.3.2.0] - 2024-05-22
 
diff --git a/libs/render_delegate/mesh.cpp b/libs/render_delegate/mesh.cpp
index e881c094e..3a8552dba 100644
--- a/libs/render_delegate/mesh.cpp
+++ b/libs/render_delegate/mesh.cpp
@@ -104,14 +104,16 @@ struct _ConvertValueToArnoldParameter<UsdType, ArnoldType, HdArnoldSampledPrimva
         if (samples.count == 0 || samples.values.empty() || !samples.values[0].IsHolding<VtArray<UsdType>>()) {
             return;
         }
-
         const VtArray<UsdType> *v0 = nullptr;
         if (requiredValues) {
             for (const auto& value : samples.values) {
-                const auto& array = value.UncheckedGet<VtArray<UsdType>>();
-                if (array.size() == *requiredValues) {
-                    v0 = &array;
-                    break;
+                // Looking for the correct buffer by size.
+                if (!value.IsEmpty()) {
+                    const auto& array = value.UncheckedGet<VtArray<UsdType>>();
+                    if (array.size() == *requiredValues) {
+                        v0 = &array;
+                        break;
+                    }
                 }
             }
         }
@@ -442,8 +444,8 @@ void HdArnoldMesh::Sync(
                 } else if (primvar.first == HdTokens->normals) {
                     if (desc.value.IsEmpty()) {
                         HdArnoldIndexedSampledPrimvarType sample;
-                        sceneDelegate->SampleIndexedPrimvar(id, primvar.first, &sample);
                         sample.count = _numberOfPositionKeys;
+                        sceneDelegate->SampleIndexedPrimvar(id, primvar.first, &sample);
                         _ConvertFaceVaryingPrimvarToBuiltin<GfVec3f, AI_TYPE_VECTOR, HdArnoldSampledPrimvarType>(
                             GetArnoldNode(), sample, sample.indices.empty() ? VtIntArray{} : sample.indices[0],
                             str::nlist, str::nidxs, &_vertexCounts, &_vertexCountSum);