imgui/examples/imgui_impl_opengl3.h

// dear imgui: Renderer for OpenGL3 / OpenGL ES2 / OpenGL ES3 (modern OpenGL with shaders / programmatic pipeline)
// This needs to be used along with a Platform Binding (e.g. GLFW, SDL, Win32, custom..)
// (Note: We are using GL3W as a helper library to access OpenGL functions since there is no standard header to access modern OpenGL functions easily. Alternatives are GLEW, Glad, etc..)

// Implemented features:
//  [X] Renderer: User texture binding. Use 'GLuint' OpenGL texture identifier as void*/ImTextureID. Read the FAQ about ImTextureID in imgui.cpp.

// You can copy and use unmodified imgui_impl_* files in your project. See main.cpp for an example of using this.
// If you are new to dear imgui, read examples/README.txt and read the documentation at the top of imgui.cpp.
// https://github.com/ocornut/imgui

// About OpenGL function loaders: 
// About OpenGL function loaders: modern OpenGL doesn't have a standard header file and requires individual function pointers to be loaded manually. 
// Helper libraries are often used for this purpose! Here we are supporting a few common ones: gl3w, glew, glad. 
// You may use another loader/header of your choice (glext, glLoadGen, etc.), or chose to manually implement your own.

// About GLSL version:
// The 'glsl_version' initialization parameter should be NULL (default) or a "#version XXX" string.
// On computer platform the GLSL version default to "#version 130". On OpenGL ES 3 platform it defaults to "#version 300 es"
// Only override if your GL version doesn't handle this GLSL version. See GLSL version table at the top of imgui_impl_opengl3.cpp.

// Set default OpenGL loader to be gl3w
#if !defined(IMGUI_IMPL_OPENGL_LOADER_GL3W)     \
 && !defined(IMGUI_IMPL_OPENGL_LOADER_GLEW)     \
 && !defined(IMGUI_IMPL_OPENGL_LOADER_GLAD)     \
 && !defined(IMGUI_IMPL_OPENGL_LOADER_CUSTOM)
#define IMGUI_IMPL_OPENGL_LOADER_GL3W
#endif

IMGUI_IMPL_API bool     ImGui_ImplOpenGL3_Init(const char* glsl_version = NULL);
IMGUI_IMPL_API void     ImGui_ImplOpenGL3_Shutdown();
IMGUI_IMPL_API void     ImGui_ImplOpenGL3_NewFrame();
IMGUI_IMPL_API void     ImGui_ImplOpenGL3_RenderDrawData(ImDrawData* draw_data);

// Called by Init/NewFrame/Shutdown
IMGUI_IMPL_API bool     ImGui_ImplOpenGL3_CreateFontsTexture();
IMGUI_IMPL_API void     ImGui_ImplOpenGL3_DestroyFontsTexture();
IMGUI_IMPL_API bool     ImGui_ImplOpenGL3_CreateDeviceObjects();
IMGUI_IMPL_API void     ImGui_ImplOpenGL3_DestroyDeviceObjects();