Add imgui

.gitmodules

@@ -0,0 +1,9 @@
+[submodule "vendor/imgui/imgui"]
+	path = vendor/imgui/imgui
+	url = https://github.com/ocornut/imgui.git
+[submodule "vendor/glfw"]
+	path = vendor/glfw
+	url = https://github.com/glfw/glfw.git
+[submodule "vendor/glew-cmake"]
+	path = vendor/glew-cmake
+	url = https://github.com/Aviii06/glew-cmake.git

vendor/CMakeLists.txt

@@ -0,0 +1,8 @@
+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(glew-cmake)
+add_subdirectory(glfw)
+add_subdirectory(imgui)

vendor/imgui/CMakeLists.txt

@@ -0,0 +1,53 @@
+cmake_minimum_required(VERSION 3.5)
+
+# Maybe stop from CMAKEing in the wrong place
+if (CMAKE_BINARY_DIR STREQUAL CMAKE_SOURCE_DIR)
+    message(FATAL_ERROR "Source and build directories cannot be the same. Go use the /build directory.")
+endif ()
+
+
+# Append Wno-error to avoid compiling imgui with Werror; imgui seems to trigger lots of warnings
+if ("${CMAKE_CXX_COMPILER_ID}" MATCHES "Clang" OR "${CMAKE_CXX_COMPILER_ID}" STREQUAL "GNU")
+    SET(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wno-error")
+
+    # apparently, this stronger command is needed to accomplish the same in Clang
+    if ("${CMAKE_CXX_COMPILER_ID}" MATCHES "Clang")
+        SET(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wno-everything")
+    endif ()
+endif ()
+
+set(SRCS imgui/imgui.cpp imgui/imgui_draw.cpp imgui/imgui_tables.cpp imgui/imgui_widgets.cpp imgui/imgui_demo.cpp imgui/backends/imgui_impl_glfw.cpp imgui/backends/imgui_impl_opengl3.cpp)
+
+add_library(
+        imgui
+        ${SRCS}
+)
+
+target_include_directories(imgui PUBLIC "${CMAKE_CURRENT_SOURCE_DIR}/imgui")
+target_include_directories(imgui PRIVATE "${CMAKE_CURRENT_SOURCE_DIR}/../glfw/include/")
+target_include_directories(imgui PRIVATE "${CMAKE_CURRENT_SOURCE_DIR}/../glad/include/")
+
+target_link_libraries(imgui PRIVATE glfw)
+
+if (APPLE)
+    # On macOS, get openGL & friends from Frameworks; do not use GLAD at all
+
+    add_definitions(-DGLFW_INCLUDE_GLCOREARB)
+
+    # NOTE: This code is essentially duplicated here and in polyscope/src/CMakeLists.txt
+
+    # Apple is playing hardball and deprecating openGL... we'll cross that bridge when we come to it
+    # Silence warnings about openGL deprecation
+    add_definitions(-DGL_SILENCE_DEPRECATION)
+    find_library(opengl_library OpenGL)
+    target_link_libraries(imgui PRIVATE ${opengl_library})
+else ()
+    # On Windows/Linux, use the glad openGL loader
+
+    add_definitions(-DIMGUI_IMPL_OPENGL_LOADER_GLAD)
+    target_link_libraries(imgui PRIVATE glad)
+endif ()
+
+
+set_target_properties(imgui PROPERTIES POSITION_INDEPENDENT_CODE TRUE)
+