Simplify re-enabling M3D build support (#5835)

* Use CMake options to control M3D source compilation

* Revert .cpp file changes (better to treat them as external 3rd party code)

* Improve documentation

---------

Co-authored-by: Steve M <[email protected]>

CMakeLists.txt

@@ -56,9 +56,19 @@ if(ASSIMP_BUILD_USE_CCACHE)
   endif()
 endif()
 
-# Disabled importers: m3d for 5.1 or later
-ADD_DEFINITIONS( -DASSIMP_BUILD_NO_M3D_IMPORTER)
-ADD_DEFINITIONS( -DASSIMP_BUILD_NO_M3D_EXPORTER)
+# User may override these in their CMake script to provide M3D import/export support
+# (M3D importer/exporter was disabled for assimp release 5.1 or later)
+option(ASSIMP_BUILD_M3D_IMPORTER "Enable M3D file import" off)
+option(ASSIMP_BUILD_M3D_EXPORTER "Enable M3D file export" off)
+
+# Internal/private M3D logic
+if (NOT ASSIMP_BUILD_M3D_IMPORTER)
+    ADD_DEFINITIONS( -DASSIMP_BUILD_NO_M3D_IMPORTER)
+endif () # if (not ASSIMP_BUILD_M3D_IMPORTER)
+if (NOT ASSIMP_BUILD_M3D_EXPORTER)
+    ADD_DEFINITIONS( -DASSIMP_BUILD_NO_M3D_EXPORTER)
+endif () # if (not ASSIMP_BUILD_M3D_EXPORTER)
+
 # Toggles the use of the hunter package manager
 option(ASSIMP_HUNTER_ENABLED "Enable Hunter package manager support" OFF)
 

code/CMakeLists.txt

@@ -416,14 +416,12 @@ ADD_ASSIMP_IMPORTER( LWS
   AssetLib/LWS/LWSLoader.h
 )
 
-ADD_ASSIMP_IMPORTER( M3D
-  AssetLib/M3D/M3DMaterials.h
-  AssetLib/M3D/M3DImporter.h
-  AssetLib/M3D/M3DImporter.cpp
-  AssetLib/M3D/M3DWrapper.h
-  AssetLib/M3D/M3DWrapper.cpp
-  AssetLib/M3D/m3d.h
-)
+if (ASSIMP_BUILD_M3D_IMPORTER)
+    ADD_ASSIMP_IMPORTER( M3D
+            AssetLib/M3D/M3DImporter.cpp
+            AssetLib/M3D/M3DWrapper.cpp
+    )
+endif () # if (ASSIMP_BUILD_M3D_IMPORTER)
 
 ADD_ASSIMP_IMPORTER( MD2
   AssetLib/MD2/MD2FileData.h
@@ -663,9 +661,10 @@ if (NOT ASSIMP_NO_EXPORT)
     AssetLib/Assxml/AssxmlFileWriter.h
     AssetLib/Assxml/AssxmlFileWriter.cpp)
 
-  ADD_ASSIMP_EXPORTER(M3D
-    AssetLib/M3D/M3DExporter.h
-    AssetLib/M3D/M3DExporter.cpp)
+  if ((NOT ASSIMP_NO_EXPORT) AND ASSIMP_BUILD_M3D_EXPORTER)
+      ADD_ASSIMP_EXPORTER(M3D
+              AssetLib/M3D/M3DExporter.cpp)
+  endif () # if (ASSIMP_BUILD_M3D_EXPORTER)
 
   ADD_ASSIMP_EXPORTER(COLLADA
     AssetLib/Collada/ColladaExporter.h