From aa25075ea4fcf64d7fbfa5af66c61226229df998 Mon Sep 17 00:00:00 2001
From: Haroon Qureshi <haroonq@google.com>
Date: Wed, 26 Nov 2025 05:32:09 -0800
Subject: [PATCH] Implement triangle geoms.

PiperOrigin-RevId: 837079122
Change-Id: If7aa0904c6f3e7c62477b75b17d67259fe2bdabb
---
 .../filament/filament/builtins.cc             | 40 +++++++++++++++++++
 src/experimental/filament/filament/builtins.h |  1 +
 .../filament/filament/drawable.cc             |  2 +
 .../filament/filament/object_manager.cc       |  1 +
 .../filament/filament/object_manager.h        |  1 +
 5 files changed, 45 insertions(+)

diff --git a/src/experimental/filament/filament/builtins.cc b/src/experimental/filament/filament/builtins.cc
index e7beacc8..8d86b7f7 100644
--- a/src/experimental/filament/filament/builtins.cc
+++ b/src/experimental/filament/filament/builtins.cc
@@ -145,6 +145,42 @@ class PlaneBuilder {
   float4 orientation_;
 };
 
+class TriangleBuilder {
+ public:
+  using VertexType = VertexNoUv;
+  using IndexType = uint16_t;
+  static constexpr filament::RenderableManager::PrimitiveType kPrimitiveType =
+      filament::RenderableManager::PrimitiveType::TRIANGLES;
+
+  TriangleBuilder()
+      : orientation_(CalculateOrientation({0, 0, 1})) {}
+
+  std::size_t NumVertices() const {
+    return 3;
+  }
+
+  std::size_t NumIndices() const {
+    return 3;
+  }
+
+  void GenerateVertices(VertexType* ptr, size_t num) const {
+    ptr[0] = VertexType({0, 0, 0}, orientation_);
+    ptr[1] = VertexType({1, 0, 0}, orientation_);
+    ptr[2] = VertexType({0, 1, 0}, orientation_);
+  }
+
+  void GenerateIndices(IndexType* ptr, size_t num) const {
+    ptr[0] = 0;
+    ptr[1] = 1;
+    ptr[2] = 2;
+  }
+
+  filament::Box GetBounds() const { return {{-1, -1, -0.001}, {1, 1, 0.001}}; }
+
+ private:
+  float4 orientation_;
+};
+
 class LineBoxBuilder {
  public:
   using VertexType = VertexNoUv;
@@ -745,6 +781,10 @@ FilamentBuffers CreatePlane(filament::Engine* engine, const mjModel* model) {
   return CreateFromBuilder(engine, PlaneBuilder(num_quads));
 }
 
+FilamentBuffers CreateTriangle(filament::Engine* engine, const mjModel* model) {
+  return CreateFromBuilder(engine, TriangleBuilder());
+}
+
 FilamentBuffers CreateBox(filament::Engine* engine, const mjModel* model) {
   const int num_quads = model->vis.quality.numquads;
   return CreateFromBuilder(engine, BoxBuilder(num_quads));
diff --git a/src/experimental/filament/filament/builtins.h b/src/experimental/filament/filament/builtins.h
index e6a8a9ed..e2ad0b4d 100644
--- a/src/experimental/filament/filament/builtins.h
+++ b/src/experimental/filament/filament/builtins.h
@@ -25,6 +25,7 @@ namespace mujoco {
 FilamentBuffers CreateLine(filament::Engine* engine, const mjModel* model);
 FilamentBuffers CreateBox(filament::Engine* engine, const mjModel* model);
 FilamentBuffers CreateLineBox(filament::Engine* engine, const mjModel* model);
+FilamentBuffers CreateTriangle(filament::Engine* engine, const mjModel* model);
 FilamentBuffers CreatePlane(filament::Engine* engine, const mjModel* model);
 FilamentBuffers CreateSphere(filament::Engine* engine, const mjModel* model);
 FilamentBuffers CreateTube(filament::Engine* engine, const mjModel* model);
diff --git a/src/experimental/filament/filament/drawable.cc b/src/experimental/filament/filament/drawable.cc
index ed1fea28..af2e4fd0 100644
--- a/src/experimental/filament/filament/drawable.cc
+++ b/src/experimental/filament/filament/drawable.cc
@@ -111,6 +111,8 @@ Drawable::Drawable(ObjectManager* object_mgr, const mjvGeom& geom)
     AddShape(ObjectManager::kLine);
   } else if (geom.type == mjGEOM_LINEBOX) {
     AddShape(ObjectManager::kLineBox);
+  } else if (geom.type == mjGEOM_TRIANGLE) {
+    AddShape(ObjectManager::kTriangle);
   } else if (geom.type == mjGEOM_FLEX || geom.type == mjGEOM_SKIN) {
     // Flex and skin geometries are dynamically updated every frame.
   } else {
diff --git a/src/experimental/filament/filament/object_manager.cc b/src/experimental/filament/filament/object_manager.cc
index 4af3625c..5e204b78 100644
--- a/src/experimental/filament/filament/object_manager.cc
+++ b/src/experimental/filament/filament/object_manager.cc
@@ -77,6 +77,7 @@ ObjectManager::ObjectManager(const mjModel* model, filament::Engine* engine,
   shapes_[kTube] = CreateTube(engine_, model_);
   shapes_[kPlane] = CreatePlane(engine_, model_);
   shapes_[kSphere] = CreateSphere(engine_, model_);
+  shapes_[kTriangle] = CreateTriangle(engine_, model_);
 
   auto LoadMaterial = [this](const char* filename) {
     Asset asset(filename, config_);
diff --git a/src/experimental/filament/filament/object_manager.h b/src/experimental/filament/filament/object_manager.h
index 40c3848a..c0e1282f 100644
--- a/src/experimental/filament/filament/object_manager.h
+++ b/src/experimental/filament/filament/object_manager.h
@@ -60,6 +60,7 @@ class ObjectManager {
     kLine,
     kLineBox,
     kPlane,
+    kTriangle,
     kBox,
     kSphere,
     kCone,