From f4bd55991f68bed06e88f1daee21917aae9cc395 Mon Sep 17 00:00:00 2001
From: Hleb Valoshka <375gnu@gmail.com>
Date: Thu, 17 Feb 2022 23:01:11 +0200
Subject: [PATCH] Optimize meshes with meshoptimizer library if available

---
 CMakeLists.txt              |  8 ++++++++
 config.h.in                 |  1 +
 src/celestia/CMakeLists.txt |  4 ++++
 src/celmodel/mesh.cpp       | 20 ++++++++++++++++++++
 src/celmodel/mesh.h         |  1 +
 src/celmodel/model.cpp      |  4 +++-
 6 files changed, 37 insertions(+), 1 deletion(-)

diff --git a/CMakeLists.txt b/CMakeLists.txt
index dcbbfaddd..12d5feb08 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -245,6 +245,14 @@ endif()
 find_package(Freetype REQUIRED)
 link_libraries(Freetype::Freetype)
 
+find_package(meshoptimizer CONFIG QUIET)
+if(meshoptimizer_FOUND)
+  message(STATUS "Found meshoptimizer library")
+  set(HAVE_MESHOPTIMIZER 1)
+else()
+  message(STATUS "meshoptimizer library is missing")
+endif()
+
 #[[
 get_cmake_property(_variableNames VARIABLES)
 list (SORT _variableNames)
diff --git a/config.h.in b/config.h.in
index ddc068989..6675c4a0d 100644
--- a/config.h.in
+++ b/config.h.in
@@ -3,4 +3,5 @@
 #cmakedefine HAVE_FLOAT_CHARCONV
 #cmakedefine HAVE_STD_FILESYSTEM
 #cmakedefine HAVE_WORDEXP
+#cmakedefine HAVE_MESHOPTIMIZER
 #cmakedefine WORDS_BIGENDIAN
diff --git a/src/celestia/CMakeLists.txt b/src/celestia/CMakeLists.txt
index 405ece35a..ddf9884d0 100644
--- a/src/celestia/CMakeLists.txt
+++ b/src/celestia/CMakeLists.txt
@@ -80,6 +80,10 @@ if(ENABLE_FFMPEG)
   target_link_libraries(celestia ${FFMPEG_LIBRARIES})
 endif()
 
+if (HAVE_MESHOPTIMIZER)
+  target_link_libraries(celestia PRIVATE meshoptimizer::meshoptimizer)
+endif()
+
 install(TARGETS celestia LIBRARY DESTINATION ${CMAKE_INSTALL_LIBDIR} NAMELINK_SKIP)
 
 add_subdirectory(glut)
diff --git a/src/celmodel/mesh.cpp b/src/celmodel/mesh.cpp
index 579f7cc00..809ebabc6 100644
--- a/src/celmodel/mesh.cpp
+++ b/src/celmodel/mesh.cpp
@@ -16,6 +16,10 @@
 #include <utility>
 #include <celutil/logger.h>
 
+#ifdef HAVE_MESHOPTIMIZER
+#include <meshoptimizer.h>
+#endif
+
 #include "mesh.h"
 
 using celestia::util::GetLogger;
@@ -455,6 +459,21 @@ Mesh::mergePrimitiveGroups()
     groups = std::move(newGroups);
 }
 
+void
+Mesh::optimize()
+{
+#ifdef HAVE_MESHOPTIMIZER
+    if (groups.size() > 1)
+        return;
+
+    auto &g = groups.front();
+
+    meshopt_optimizeVertexCache(g.indices.data(), g.indices.data(), g.indices.size(), nVertices);
+    meshopt_optimizeOverdraw(g.indices.data(), g.indices.data(), g.indices.size(), reinterpret_cast<float*>(vertices.data()), nVertices, vertexDesc.strideBytes, 1.05f);
+    meshopt_optimizeVertexFetch(vertices.data(), g.indices.data(), g.indices.size(), vertices.data(), nVertices, vertexDesc.strideBytes);
+#endif
+}
+
 bool
 Mesh::pick(const Eigen::Vector3d& rayOrigin, const Eigen::Vector3d& rayDirection, PickResult* result) const
 {
@@ -769,4 +788,5 @@ Mesh::canMerge(const Mesh &other, const std::vector<Material> &materials) const
 
     return true;
 }
+
 } // end namespace cmod
diff --git a/src/celmodel/mesh.h b/src/celmodel/mesh.h
index 68dbb2945..be3cd2bfa 100644
--- a/src/celmodel/mesh.h
+++ b/src/celmodel/mesh.h
@@ -239,6 +239,7 @@ class Mesh
 
     void merge(const Mesh&);
     bool canMerge(const Mesh&, const std::vector<Material> &materials) const;
+    void optimize();
 
  private:
     PrimitiveGroup createLinePrimitiveGroup(bool lineStrip, const std::vector<Index32>& indices);
diff --git a/src/celmodel/model.cpp b/src/celmodel/model.cpp
index def26e852..81ca1c23c 100644
--- a/src/celmodel/model.cpp
+++ b/src/celmodel/model.cpp
@@ -318,7 +318,6 @@ Model::usesTextureType(TextureSemantic t) const
 }
 
 
-
 bool
 Model::OpacityComparator::operator()(const Mesh& a, const Mesh& b) const
 {
@@ -353,6 +352,9 @@ Model::sortMeshes(const MeshComparator& comparator)
         p.merge(meshes[i]);
     }
     GetLogger()->info("Merged similar meshes: {} -> {}.\n", meshes.size(), newMeshes.size());
+
+    for (auto &mesh : newMeshes)
+        mesh.optimize();
     meshes = std::move(newMeshes);
 }