Add LRZ QEM simplification

Author: jasonlmfong

Model-Modifier/CMakeLists.txt

@@ -485,6 +485,7 @@ set(Source_Files
     "src/scene/surface/Surface_CatmullClark.cpp"
     "src/scene/surface/Surface_DooSabin.cpp"
     "src/scene/surface/Surface_GarlandHeckbert.cpp"
+    "src/scene/surface/Surface_LiuRahimzadehZordan.cpp"
     "src/scene/surface/Surface_Loop.cpp"
     "src/scene/util/OrderVertices.cpp"
     "src/scene/util/PlaneProjection.cpp"

Model-Modifier/gallery/Screenshot_2025-11-23_0750.png

@@ -380,6 +380,20 @@ int main()
             ImGui::Indent();
             ImGui::SliderInt("Desired count", &desiredTriCount, triCount/5, triCount);
             ImGui::Unindent();
+            if (ImGui::Button("Liu Rahimzadeh Zordan Simplification Surface"))
+            {
+                obj.MakeTriangleMesh(); // Triangulate first
+                Surface LRZ(obj);
+                static float alpha = 0.5f; // default balanced weight
+                obj = LRZ.LineQEM(desiredTriCount, alpha);
+                ModifyModel = true;
+            }
+            ImGui::Indent();
+            ImGui::SliderInt("Desired count", &desiredTriCount, triCount/5, triCount);
+            static float alpha = 0.5f;
+            ImGui::SliderFloat("Alpha (edge preservation)", &alpha, 0.0f, 1.0f);
+            ImGui::Text("0.0 = smooth, 0.5 = balanced, 1.0 = sharp edges");
+            ImGui::Unindent();
 
             ImGui::Unindent();
         }

Model-Modifier/src/main.cpp

@@ -46,6 +46,9 @@ struct ValidPair
 	bool edge;
 	float error;
 	glm::vec3 newVert;
+	// weight parameter balancing point vs line quadrics
+	// only for augmented version
+	float alpha;
 };
 
 struct CompareValidPairs
@@ -80,11 +83,16 @@ class Surface
 		std::unordered_map<unsigned int, std::vector<glm::vec3>> pointsPerEdge
 	);
 	Object LoOutputOBJ(std::vector<glm::vec3> edgePoints);
-	glm::mat4 ComputeQuadric(VertexRecord v0);
+	// Shared QEM helpers
+	glm::mat4 ComputePlaneQuadric(VertexRecord v0);
 	glm::mat4 BuildQuadricSolverMatrix(const glm::mat4& Quad);
 	void ComputeOptimalVertexAndError(ValidPair& validPair, const glm::mat4& quadric1, const glm::mat4& quadric2);
 	void UpdateAdjacencyIndices(std::vector<unsigned int>& adjFaces, const std::vector<unsigned int>& removedFaceIndices);
-	Object GHOutputOBJ();
+	Object QEMOutputOBJ();  // shared output builder for both QEM variants
+	// Line Quadric specific helpers
+	glm::vec3 ComputeVertexNormal(VertexRecord v0);
+	glm::mat4 ComputeLineQuadric(VertexRecord v0);
+	glm::mat4 ComputeWeightedQuadric(const glm::mat4& planeQuadric, const glm::mat4& lineQuadric, float alpha);
 
 	// Modification algorithms
 	Object Beehive();
@@ -93,6 +101,7 @@ class Surface
 	Object DooSabin();
 	Object Loop();
 	Object QEM(unsigned int desiredCount);
+	Object LineQEM(unsigned int desiredCount, float alpha = 0.5f);
 
 public:
 	std::vector<VertexRecord> m_Vertices;

Model-Modifier/src/scene/surface/Surface.h

@@ -3,7 +3,8 @@
 
 ////////// helpers to build the Object //////////
 
-Object Surface::GHOutputOBJ()
+// Shared output builder for both QEM and LineQEM
+Object Surface::QEMOutputOBJ()
 {
     // build new Object class
     std::vector<glm::vec3> VertexPos;
@@ -53,7 +54,7 @@ Object Surface::GHOutputOBJ()
 ////////// helpers for the GH algorithm //////////
 
 // computer quadric matrix by summing all K_p matrices of a vertice v0
-glm::mat4 Surface::ComputeQuadric(VertexRecord v0)
+glm::mat4 Surface::ComputePlaneQuadric(VertexRecord v0)
 {
     glm::mat4 quadric{ 0.0f };
     // for each neighbouring face, compute K_p
@@ -179,7 +180,7 @@ Object Surface::QEM(unsigned int desiredCount)
 
     for (unsigned int i = 0; i < numVertices; i++)
     {
-        glm::mat4 quadric = ComputeQuadric(m_Vertices[i]);
+        glm::mat4 quadric = ComputePlaneQuadric(m_Vertices[i]);
 
         // add penalty quadric for boundary vertices
         bool isBoundaryVertex = false;
@@ -517,5 +518,5 @@ Object Surface::QEM(unsigned int desiredCount)
         }
     }
 
-    return GHOutputOBJ();
+    return QEMOutputOBJ();
 }