feat: LOD mesh generation + incremental BVH

2026-07-24 16:14:09 +00:00
parent 5a2f01f597
commit e02c5980b4
7 changed files with 455 additions and 0 deletions
@@ -0,0 +1,79 @@
+#pragma once
+#include "vde/mesh/halfedge_mesh.h"
+#include <vector>
+#include <string>
+
+namespace vde::brep { class BrepModel; }
+
+namespace vde::mesh {
+
+/**
+ * @brief Level-of-detail mesh with multiple detail levels
+ *
+ * Stores a sequence of simplified meshes from highest detail (index 0)
+ * to lowest. Screen-space error thresholds determine which level to
+ * use for rendering.
+ *
+ * @ingroup mesh
+ */
+struct LODMesh {
+    std::string name;
+    /// Meshes from highest detail (index 0) to lowest
+    std::vector<HalfedgeMesh> levels;
+    /// Screen-space error thresholds for each level (in pixels)
+    std::vector<double> thresholds;
+
+    /**
+     * @brief Get the appropriate LOD level for a given screen-space error
+     *
+     * Selects the lowest-detail level whose threshold is ≤ error.
+     * Walks thresholds from coarsest to finest.
+     *
+     * @param error Screen-space error in pixels
+     * @return LOD level index (0 = highest detail)
+     */
+    [[nodiscard]] int level_for_error(double error) const;
+
+    /**
+     * @brief Get the mesh at a specific LOD level (clamped)
+     *
+     * @param level Desired LOD level
+     * @return Reference to the mesh at that level
+     */
+    [[nodiscard]] const HalfedgeMesh& mesh_at(int level) const;
+};
+
+/**
+ * @brief Generate LOD meshes from a high-detail mesh
+ *
+ * Iteratively applies QEM simplification, reducing face count
+ * by `reduction_ratio` at each level.
+ *
+ * @param mesh High-detail input mesh
+ * @param num_levels Number of LOD levels (including base)
+ * @param reduction_ratio Ratio of faces to keep at each level (0.5 = half)
+ * @return LOD meshes with thresholds proportional to level index
+ *
+ * @code{.cpp}
+ * auto lod = generate_lod(high_res, 4, 0.5);
+ * int level = lod.level_for_error(screen_error);
+ * render(lod.mesh_at(level));
+ * @endcode
+ */
+[[nodiscard]] LODMesh generate_lod(const HalfedgeMesh& mesh,
+    int num_levels = 3, double reduction_ratio = 0.5);
+
+/**
+ * @brief Generate LOD from B-Rep body (tessellate + simplify)
+ *
+ * Tessellates the B-Rep body with default deflection, then
+ * generates LOD levels via QEM simplification.
+ *
+ * @param body B-Rep model
+ * @param num_levels Number of LOD levels
+ * @return LOD meshes
+ */
+[[nodiscard]] LODMesh generate_brep_lod(const brep::BrepModel& body,
+    int num_levels = 3);
+
+} // namespace vde::mesh