ad QEM simplification

Author: jasonlmfong

Model-Modifier/CMakeLists.txt

@@ -484,6 +484,7 @@ set(Source_Files
     "src/scene/surface/Surface.cpp"
     "src/scene/surface/Surface_CatmullClark.cpp"
     "src/scene/surface/Surface_DooSabin.cpp"
+    "src/scene/surface/Surface_GarlandHeckbert.cpp"
     "src/scene/surface/Surface_Loop.cpp"
     "src/scene/util/OrderVertices.cpp"
     "src/scene/util/PlaneProjection.cpp"

Model-Modifier/gallery/Screenshot_2025-11-22_1549.png

@@ -135,6 +135,10 @@ int main()
     Object obj = objects.findObj(currObject);
     Material meshMat;
 
+    // object triangle count (QEM)
+    int triCount = static_cast<int>(obj.m_TriFaceIndices.size());
+    int desiredTriCount = triCount;
+
     VertexBufferLayout layout;
     layout.Push<float>(3); // 3d coordinates
     layout.Push<float>(3); // normals
@@ -366,17 +370,17 @@ int main()
                 obj = Lo.Loop();
                 ModifyModel = true;
             }
-            //if (ImGui::Button("Garland Heckbert Simplication Surface"))
-            //{
-            //    Surface GH(obj);
-            //    obj = GH.QEM();
-            //    mesh.Rebuild(obj); // rebuild mesh based on object info
-            //    numFaces = static_cast<unsigned int>(mesh.m_Object.m_FaceIndices.size()); // update number of faces
-
-            //    objectVA.Bind();
-            //    objectVB.AssignData(mesh.m_OutVertices, mesh.m_OutNumVert * sizeof(float), DRAW_MODE::STATIC);
-            //    objectIB.AssignData(mesh.m_OutIndices, mesh.m_OutNumIdx, DRAW_MODE::STATIC);
-            //}
+            if (ImGui::Button("Garland Heckbert Simplification Surface"))
+            {
+                obj.MakeTriangleMesh(); // Triangulate first
+                Surface GH(obj);
+                obj = GH.QEM(desiredTriCount);
+                ModifyModel = true;
+            }
+            ImGui::Indent();
+            ImGui::SliderInt("Desired count", &desiredTriCount, triCount/5, triCount);
+            ImGui::Unindent();
+
             ImGui::Unindent();
         }
 
@@ -626,6 +630,7 @@ int main()
             currObject = nextObject;
 
             obj = objects.findObj(currObject); // search for the object requested
+            triCount = static_cast<int>(obj.m_TriFaceIndices.size()); desiredTriCount = triCount;
 
             ModifyModel = true;
         }
@@ -635,6 +640,7 @@ int main()
         {
             mesh.Rebuild(obj); // rebuild mesh based on object info
             numFaces = static_cast<unsigned int>(mesh.m_Object.m_FaceIndices.size()); // update number of faces
+            triCount = static_cast<int>(obj.m_TriFaceIndices.size()); desiredTriCount = triCount;
 
             objectVA.Bind();
             objectVB.AssignData(mesh.m_OutVertices, mesh.m_OutNumVert * sizeof(float), DRAW_MODE::STATIC);

Model-Modifier/src/main.cpp

@@ -137,21 +137,3 @@ glm::vec3 Surface::ComputeFaceNormal(glm::vec3 pos0, glm::vec3 pos1, glm::vec3 p
 {
     return glm::normalize(glm::cross(pos1 - pos0, pos2 - pos0));
 }
-
-// computer quadric matrix by summing all K_p matrices of a vertice v0
-glm::mat4 Surface::ComputeQuadric(VertexRecord v0)
-{
-    glm::mat4 quadric{ 0.0f };
-    // for each neighbouring face, compute K_p
-    glm::vec3 position = v0.position;
-    for (unsigned int faceIdx : v0.adjFacesIdx)
-    {
-        FaceRecord face = m_Faces[faceIdx];
-        glm::vec3 faceNormal = ComputeFaceNormal(face);
-        glm::vec4 plane{ faceNormal, -glm::dot(faceNormal, position) }; // plane equation ax+by+cz+d = 0
-
-        quadric += glm::outerProduct(plane, plane); // K_p
-    }
-
-    return quadric;
-}

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

@@ -3,6 +3,7 @@
 #include <set>
 #include <vector>
 #include <unordered_map>
+#include <queue>
 
 #include "../../external/glm/ext/vector_float3.hpp"
 #include "../../external/glm/ext/vector_uint2.hpp"
@@ -37,6 +38,24 @@ struct FaceRecord
 	std::vector<unsigned int> edgesIdx; // each face can have n edges
 };
 
+// QEM
+struct ValidPair
+{
+	unsigned int vertOne;
+	unsigned int vertTwo;
+	bool edge;
+	float error;
+	glm::vec3 newVert;
+};
+
+struct CompareValidPairs
+{
+	bool operator()(const ValidPair& a, const ValidPair& b) const
+	{
+		return a.error > b.error; // min heap
+	}
+};
+
 class Surface
 {
 public:
@@ -62,14 +81,18 @@ class Surface
 	);
 	Object LoOutputOBJ(std::vector<glm::vec3> edgePoints);
 	glm::mat4 ComputeQuadric(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();
 
 	// Modification algorithms
 	Object Beehive();
 	Object Snowflake();
 	Object CatmullClark();
 	Object DooSabin();
 	Object Loop();
-	Object QEM();
+	Object QEM(unsigned int desiredCount);
 
 public:
 	std::vector<VertexRecord> m_Vertices;
@@ -80,4 +103,6 @@ class Surface
 	glm::vec3 m_Max;
 
 	std::unordered_map<unsigned int, std::unordered_map<unsigned int, unsigned int>> m_EdgeIdxLookup;
+private:
+	std::priority_queue<ValidPair, std::vector<ValidPair>, CompareValidPairs> m_QuadricErrorHeap;
 };