From e5c8c2c9910a8a9a6e4ccd775546b238f00d4ee0 Mon Sep 17 00:00:00 2001
From: "Jeongseok (JS) Lee" <jslee02@users.noreply.github.com>
Date: Mon, 2 Sep 2024 19:50:41 -0700
Subject: [PATCH] Allow negative scale for MeshShape (#1841)

---
 dart/dynamics/MeshShape.cpp      | 46 +++++++++++++-------------------
 dart/dynamics/MeshShape.hpp      | 16 +++++++++++
 python/dartpy/dynamics/Shape.cpp | 11 +++++---
 3 files changed, 42 insertions(+), 31 deletions(-)

diff --git a/dart/dynamics/MeshShape.cpp b/dart/dynamics/MeshShape.cpp
index e960b4e971a90..de95aad749ad6 100644
--- a/dart/dynamics/MeshShape.cpp
+++ b/dart/dynamics/MeshShape.cpp
@@ -236,8 +236,6 @@ void MeshShape::setMesh(
 //==============================================================================
 void MeshShape::setScale(const Eigen::Vector3d& scale)
 {
-  assert((scale.array() > 0.0).all());
-
   mScale = scale;
   mIsBoundingBoxDirty = true;
   mIsVolumeDirty = true;
@@ -245,6 +243,12 @@ void MeshShape::setScale(const Eigen::Vector3d& scale)
   incrementVersion();
 }
 
+//==============================================================================
+void MeshShape::setScale(const double scale)
+{
+  setScale(Eigen::Vector3d::Constant(scale));
+}
+
 //==============================================================================
 const Eigen::Vector3d& MeshShape::getScale() const
 {
@@ -332,33 +336,21 @@ void MeshShape::updateBoundingBox() const
     return;
   }
 
-  double max_X = -std::numeric_limits<double>::infinity();
-  double max_Y = -std::numeric_limits<double>::infinity();
-  double max_Z = -std::numeric_limits<double>::infinity();
-  double min_X = std::numeric_limits<double>::infinity();
-  double min_Y = std::numeric_limits<double>::infinity();
-  double min_Z = std::numeric_limits<double>::infinity();
-
-  for (unsigned int i = 0; i < mMesh->mNumMeshes; i++) {
-    for (unsigned int j = 0; j < mMesh->mMeshes[i]->mNumVertices; j++) {
-      if (mMesh->mMeshes[i]->mVertices[j].x > max_X)
-        max_X = mMesh->mMeshes[i]->mVertices[j].x;
-      if (mMesh->mMeshes[i]->mVertices[j].x < min_X)
-        min_X = mMesh->mMeshes[i]->mVertices[j].x;
-      if (mMesh->mMeshes[i]->mVertices[j].y > max_Y)
-        max_Y = mMesh->mMeshes[i]->mVertices[j].y;
-      if (mMesh->mMeshes[i]->mVertices[j].y < min_Y)
-        min_Y = mMesh->mMeshes[i]->mVertices[j].y;
-      if (mMesh->mMeshes[i]->mVertices[j].z > max_Z)
-        max_Z = mMesh->mMeshes[i]->mVertices[j].z;
-      if (mMesh->mMeshes[i]->mVertices[j].z < min_Z)
-        min_Z = mMesh->mMeshes[i]->mVertices[j].z;
+  Eigen::Vector3d minPoint
+      = Eigen::Vector3d::Constant(std::numeric_limits<double>::infinity());
+  Eigen::Vector3d maxPoint = -minPoint;
+
+  for (unsigned i = 0u; i < mMesh->mNumMeshes; i++) {
+    for (unsigned j = 0u; j < mMesh->mMeshes[i]->mNumVertices; j++) {
+      const auto& vertex = mMesh->mMeshes[i]->mVertices[j];
+      const Eigen::Vector3d eigenVertex(vertex.x, vertex.y, vertex.z);
+      minPoint = minPoint.cwiseMin(eigenVertex.cwiseProduct(mScale));
+      maxPoint = maxPoint.cwiseMax(eigenVertex.cwiseProduct(mScale));
     }
   }
-  mBoundingBox.setMin(
-      Eigen::Vector3d(min_X * mScale[0], min_Y * mScale[1], min_Z * mScale[2]));
-  mBoundingBox.setMax(
-      Eigen::Vector3d(max_X * mScale[0], max_Y * mScale[1], max_Z * mScale[2]));
+
+  mBoundingBox.setMin(minPoint);
+  mBoundingBox.setMax(maxPoint);
 
   mIsBoundingBoxDirty = false;
 }
diff --git a/dart/dynamics/MeshShape.hpp b/dart/dynamics/MeshShape.hpp
index acf4b9e39c84b..c2dd54dd3b4e9 100644
--- a/dart/dynamics/MeshShape.hpp
+++ b/dart/dynamics/MeshShape.hpp
@@ -124,8 +124,24 @@ class MeshShape : public Shape
 
   common::ResourceRetrieverPtr getResourceRetriever();
 
+  /// Sets the scale of the object using a 3D vector.
+  ///
+  /// The scale is applied independently along each axis (x, y, z). Negative
+  /// values will mirror the object along the corresponding axis, potentially
+  /// flipping normals and causing inside-out geometry.
+  ///
+  /// Use caution when applying negative scales as it may affect rendering and
+  /// physics calculations.
   void setScale(const Eigen::Vector3d& scale);
 
+  /// Sets a uniform scale for the object across all axes.
+  void setScale(double scale);
+
+  /// Returns the current scale of the object as a 3D vector.
+  ///
+  /// Each component of the vector represents the scale factor along the
+  /// corresponding axis (x, y, z). Negative values indicate that the object has
+  /// been mirrored along that axis.
   const Eigen::Vector3d& getScale() const;
 
   /// Set how the color of this mesh should be determined
diff --git a/python/dartpy/dynamics/Shape.cpp b/python/dartpy/dynamics/Shape.cpp
index bf39f02360cce..ae6d4270a1855 100644
--- a/python/dartpy/dynamics/Shape.cpp
+++ b/python/dartpy/dynamics/Shape.cpp
@@ -399,10 +399,13 @@ void Shape(py::module& m)
           })
       .def(
           "setScale",
-          +[](dart::dynamics::MeshShape* self, const Eigen::Vector3d& scale) {
-            self->setScale(scale);
-          },
-          ::py::arg("scale"))
+          py::overload_cast<const Eigen::Vector3d&>(
+              &dart::dynamics::MeshShape::setScale),
+          py::arg("scale"))
+      .def(
+          "setScale",
+          py::overload_cast<double>(&dart::dynamics::MeshShape::setScale),
+          py::arg("scale"))
       .def(
           "getScale",
           +[](const dart::dynamics::MeshShape* self) -> const Eigen::Vector3d& {