Update CMake dependencies to rely on proper targets

.gitmodules

@@ -9,3 +9,6 @@
 [submodule "deps/happly"]
 	path = deps/happly
 	url = https://github.com/nmwsharp/happly.git
+[submodule "deps/glm"]
+	path = deps/glm
+	url = https://github.com/g-truc/glm.git

deps/CMakeLists.txt

@@ -1,23 +1,41 @@
 if("${POLYSCOPE_BACKEND_OPENGL3_GLFW}")
 
   ## Glad
-  add_subdirectory(glad)
+  if(NOT TARGET glad)
+    add_subdirectory(glad)
+  endif()
 
   ## GLFW
-  set(GLFW_BUILD_DOCS OFF CACHE BOOL "" FORCE)
-  set(GLFW_BUILD_TESTS OFF CACHE BOOL "" FORCE)
-  set(GLFW_BUILD_EXAMPLES OFF CACHE BOOL "" FORCE)
-  set(GLFW_INSTALL OFF CACHE BOOL "" FORCE)
-  add_subdirectory(glfw)
+  if(NOT TARGET glfw)
+    set(GLFW_BUILD_DOCS OFF CACHE BOOL "" FORCE)
+    set(GLFW_BUILD_TESTS OFF CACHE BOOL "" FORCE)
+    set(GLFW_BUILD_EXAMPLES OFF CACHE BOOL "" FORCE)
+    set(GLFW_INSTALL OFF CACHE BOOL "" FORCE)
+    add_subdirectory(glfw)
+  endif()
 endif()
 
-if("${POLYSCOPE_BACKEND_OPENGL_MOCK}")
+## glm
+if(NOT TARGET glm::glm)
+  add_subdirectory(glm)
 endif()
 
 ## Imgui
-add_subdirectory(imgui)
+if(NOT TARGET imgui)
+  add_subdirectory(imgui)
+endif()
 
-## Argparse
+## Json
+if(NOT TARGET nlohmann_json::nlohmann_json)
+  add_subdirectory(json)
+endif()
 
-## Other dependencies
-add_subdirectory(stb)
+## MarchingCube
+if(NOT TARGET MarchingCube::MarchingCube)
+  add_subdirectory(MarchingCubeCpp)
+endif()
+
+## stb
+if(NOT TARGET stb)
+  add_subdirectory(stb)
+endif()

deps/MarchingCubeCpp/CMakeLists.txt

@@ -0,0 +1,4 @@
+add_library(MarchingCube INTERFACE)
+add_library(MarchingCube::MarchingCube ALIAS MarchingCube)
+
+target_include_directories(MarchingCube INTERFACE include)

deps/glad/src/CMakeLists.txt

@@ -13,6 +13,6 @@ if (library_type STREQUAL SHARED_LIBRARY)
   target_compile_definitions(glad PUBLIC GLAD_GLAPI_EXPORT PRIVATE GLAD_GLAPI_EXPORT_BUILD)
 endif()
 
-target_include_directories(glad PRIVATE "../include")    
+target_include_directories(glad PUBLIC "../include")
 
 set_target_properties(glad PROPERTIES POSITION_INDEPENDENT_CODE TRUE)