examples/example_glut_opengl2/main.cpp - external/github.com/ocornut/imgui - Git at Google

 // dear imgui: standalone example application for GLUT/FreeGLUT + OpenGL2, using legacy fixed pipeline
 // If you are new to dear imgui, see examples/README.txt and documentation at the top of imgui.cpp.

 // !!! GLUT/FreeGLUT IS OBSOLETE SOFTWARE. Using GLUT is not recommended unless you really miss the 90's. !!!
 // !!! If someone or something is teaching you GLUT in 2020, you are being abused. Please show some resistance. !!!
 // !!! Nowadays, prefer using GLFW or SDL instead!

 #include "imgui.h"
 #include "imgui_impl_glut.h"
 #include "imgui_impl_opengl2.h"
 #ifdef __APPLE__
     #include <GLUT/glut.h>
 #else
     #include <GL/freeglut.h>
 #endif

 #ifdef _MSC_VER
 #pragma warning (disable: 4505) // unreferenced local function has been removed
 #endif

 // Our state
 static bool show_demo_window = true;
 static bool show_another_window = false;
 static ImVec4 clear_color = ImVec4(0.45f, 0.55f, 0.60f, 1.00f);

 void my_display_code()
 {
     // 1. Show the big demo window (Most of the sample code is in ImGui::ShowDemoWindow()! You can browse its code to learn more about Dear ImGui!).
     if (show_demo_window)
         ImGui::ShowDemoWindow(&show_demo_window);

     // 2. Show a simple window that we create ourselves. We use a Begin/End pair to created a named window.
     {
         static float f = 0.0f;
         static int counter = 0;

         ImGui::Begin("Hello, world!");                          // Create a window called "Hello, world!" and append into it.

         ImGui::Text("This is some useful text.");               // Display some text (you can use a format strings too)
         ImGui::Checkbox("Demo Window", &show_demo_window);      // Edit bools storing our window open/close state
         ImGui::Checkbox("Another Window", &show_another_window);

         ImGui::SliderFloat("float", &f, 0.0f, 1.0f);            // Edit 1 float using a slider from 0.0f to 1.0f
         ImGui::ColorEdit3("clear color", (float*)&clear_color); // Edit 3 floats representing a color

         if (ImGui::Button("Button"))                            // Buttons return true when clicked (most widgets return true when edited/activated)
             counter++;
         ImGui::SameLine();
         ImGui::Text("counter = %d", counter);

         ImGui::Text("Application average %.3f ms/frame (%.1f FPS)", 1000.0f / ImGui::GetIO().Framerate, ImGui::GetIO().Framerate);
         ImGui::End();
     }

     // 3. Show another simple window.
     if (show_another_window)
     {
         ImGui::Begin("Another Window", &show_another_window);   // Pass a pointer to our bool variable (the window will have a closing button that will clear the bool when clicked)
         ImGui::Text("Hello from another window!");
         if (ImGui::Button("Close Me"))
             show_another_window = false;
         ImGui::End();
     }
 }

 void glut_display_func()
 {
     // Start the Dear ImGui frame
     ImGui_ImplOpenGL2_NewFrame();
     ImGui_ImplGLUT_NewFrame();

     my_display_code();

     // Rendering
     ImGui::Render();
     ImGuiIO& io = ImGui::GetIO();
     glViewport(0, 0, (GLsizei)io.DisplaySize.x, (GLsizei)io.DisplaySize.y);
     glClearColor(clear_color.x, clear_color.y, clear_color.z, clear_color.w);
     glClear(GL_COLOR_BUFFER_BIT);
     //glUseProgram(0); // You may want this if using this code in an OpenGL 3+ context where shaders may be bound, but prefer using the GL3+ code.
     ImGui_ImplOpenGL2_RenderDrawData(ImGui::GetDrawData());

     glutSwapBuffers();
     glutPostRedisplay();
 }

 // You can read the io.WantCaptureMouse, io.WantCaptureKeyboard flags to tell if dear imgui wants to use your inputs.
 // - When io.WantCaptureMouse is true, do not dispatch mouse input data to your main application.
 // - When io.WantCaptureKeyboard is true, do not dispatch keyboard input data to your main application.
 // Generally you may always pass all inputs to dear imgui, and hide them from your application based on those two flags.

 int main(int argc, char** argv)
 {
     // Create GLUT window
     glutInit(&argc, argv);
 #ifdef __FREEGLUT_EXT_H__
     glutSetOption(GLUT_ACTION_ON_WINDOW_CLOSE, GLUT_ACTION_GLUTMAINLOOP_RETURNS);
 #endif
     glutInitDisplayMode(GLUT_RGBA | GLUT_DOUBLE | GLUT_MULTISAMPLE);
     glutInitWindowSize(1280, 720);
     glutCreateWindow("Dear ImGui GLUT+OpenGL2 Example");

     // Setup GLUT display function
     // We will also call ImGui_ImplGLUT_InstallFuncs() to get all the other functions installed for us,
     // otherwise it is possible to install our own functions and call the imgui_impl_glut.h functions ourselves.
     glutDisplayFunc(glut_display_func);

     // Setup Dear ImGui context
     IMGUI_CHECKVERSION();
     ImGui::CreateContext();
     ImGuiIO& io = ImGui::GetIO(); (void)io;
     //io.ConfigFlags |= ImGuiConfigFlags_NavEnableKeyboard;     // Enable Keyboard Controls

     // Setup Dear ImGui style
     ImGui::StyleColorsDark();
     //ImGui::StyleColorsClassic();

     // Setup Platform/Renderer bindings
     ImGui_ImplGLUT_Init();
     ImGui_ImplGLUT_InstallFuncs();
     ImGui_ImplOpenGL2_Init();

     // Load Fonts
     // - If no fonts are loaded, dear imgui will use the default font. You can also load multiple fonts and use ImGui::PushFont()/PopFont() to select them.
     // - AddFontFromFileTTF() will return the ImFont* so you can store it if you need to select the font among multiple.
     // - If the file cannot be loaded, the function will return NULL. Please handle those errors in your application (e.g. use an assertion, or display an error and quit).
     // - The fonts will be rasterized at a given size (w/ oversampling) and stored into a texture when calling ImFontAtlas::Build()/GetTexDataAsXXXX(), which ImGui_ImplXXXX_NewFrame below will call.
     // - Read 'docs/FONTS.md' for more instructions and details.
     // - Remember that in C/C++ if you want to include a backslash \ in a string literal you need to write a double backslash \\ !
     //io.Fonts->AddFontDefault();
     //io.Fonts->AddFontFromFileTTF("../../misc/fonts/Roboto-Medium.ttf", 16.0f);
     //io.Fonts->AddFontFromFileTTF("../../misc/fonts/Cousine-Regular.ttf", 15.0f);
     //io.Fonts->AddFontFromFileTTF("../../misc/fonts/DroidSans.ttf", 16.0f);
     //io.Fonts->AddFontFromFileTTF("../../misc/fonts/ProggyTiny.ttf", 10.0f);
     //ImFont* font = io.Fonts->AddFontFromFileTTF("c:\\Windows\\Fonts\\ArialUni.ttf", 18.0f, NULL, io.Fonts->GetGlyphRangesJapanese());
     //IM_ASSERT(font != NULL);

     glutMainLoop();

     // Cleanup
     ImGui_ImplOpenGL2_Shutdown();
     ImGui_ImplGLUT_Shutdown();
     ImGui::DestroyContext();

     return 0;
 }
	// dear imgui: standalone example application for GLUT/FreeGLUT + OpenGL2, using legacy fixed pipeline
	// If you are new to dear imgui, see examples/README.txt and documentation at the top of imgui.cpp.

	// !!! GLUT/FreeGLUT IS OBSOLETE SOFTWARE. Using GLUT is not recommended unless you really miss the 90's. !!!
	// !!! If someone or something is teaching you GLUT in 2020, you are being abused. Please show some resistance. !!!
	// !!! Nowadays, prefer using GLFW or SDL instead!

	#include "imgui.h"
	#include "imgui_impl_glut.h"
	#include "imgui_impl_opengl2.h"
	#ifdef __APPLE__
	#include <GLUT/glut.h>
	#else
	#include <GL/freeglut.h>
	#endif

	#ifdef _MSC_VER
	#pragma warning (disable: 4505) // unreferenced local function has been removed
	#endif

	// Our state
	static bool show_demo_window = true;
	static bool show_another_window = false;
	static ImVec4 clear_color = ImVec4(0.45f, 0.55f, 0.60f, 1.00f);

	void my_display_code()
	{
	// 1. Show the big demo window (Most of the sample code is in ImGui::ShowDemoWindow()! You can browse its code to learn more about Dear ImGui!).
	if (show_demo_window)
	ImGui::ShowDemoWindow(&show_demo_window);

	// 2. Show a simple window that we create ourselves. We use a Begin/End pair to created a named window.
	{
	static float f = 0.0f;
	static int counter = 0;

	ImGui::Begin("Hello, world!"); // Create a window called "Hello, world!" and append into it.

	ImGui::Text("This is some useful text."); // Display some text (you can use a format strings too)
	ImGui::Checkbox("Demo Window", &show_demo_window); // Edit bools storing our window open/close state
	ImGui::Checkbox("Another Window", &show_another_window);

	ImGui::SliderFloat("float", &f, 0.0f, 1.0f); // Edit 1 float using a slider from 0.0f to 1.0f
	ImGui::ColorEdit3("clear color", (float*)&clear_color); // Edit 3 floats representing a color

	if (ImGui::Button("Button")) // Buttons return true when clicked (most widgets return true when edited/activated)
	counter++;
	ImGui::SameLine();
	ImGui::Text("counter = %d", counter);

	ImGui::Text("Application average %.3f ms/frame (%.1f FPS)", 1000.0f / ImGui::GetIO().Framerate, ImGui::GetIO().Framerate);
	ImGui::End();
	}

	// 3. Show another simple window.
	if (show_another_window)
	{
	ImGui::Begin("Another Window", &show_another_window); // Pass a pointer to our bool variable (the window will have a closing button that will clear the bool when clicked)
	ImGui::Text("Hello from another window!");
	if (ImGui::Button("Close Me"))
	show_another_window = false;
	ImGui::End();
	}
	}

	void glut_display_func()
	{
	// Start the Dear ImGui frame
	ImGui_ImplOpenGL2_NewFrame();
	ImGui_ImplGLUT_NewFrame();

	my_display_code();

	// Rendering
	ImGui::Render();
	ImGuiIO& io = ImGui::GetIO();
	glViewport(0, 0, (GLsizei)io.DisplaySize.x, (GLsizei)io.DisplaySize.y);
	glClearColor(clear_color.x, clear_color.y, clear_color.z, clear_color.w);
	glClear(GL_COLOR_BUFFER_BIT);
	//glUseProgram(0); // You may want this if using this code in an OpenGL 3+ context where shaders may be bound, but prefer using the GL3+ code.
	ImGui_ImplOpenGL2_RenderDrawData(ImGui::GetDrawData());

	glutSwapBuffers();
	glutPostRedisplay();
	}

	// You can read the io.WantCaptureMouse, io.WantCaptureKeyboard flags to tell if dear imgui wants to use your inputs.
	// - When io.WantCaptureMouse is true, do not dispatch mouse input data to your main application.
	// - When io.WantCaptureKeyboard is true, do not dispatch keyboard input data to your main application.
	// Generally you may always pass all inputs to dear imgui, and hide them from your application based on those two flags.

	int main(int argc, char** argv)
	{
	// Create GLUT window
	glutInit(&argc, argv);
	#ifdef __FREEGLUT_EXT_H__
	glutSetOption(GLUT_ACTION_ON_WINDOW_CLOSE, GLUT_ACTION_GLUTMAINLOOP_RETURNS);
	#endif
	glutInitDisplayMode(GLUT_RGBA \| GLUT_DOUBLE \| GLUT_MULTISAMPLE);
	glutInitWindowSize(1280, 720);
	glutCreateWindow("Dear ImGui GLUT+OpenGL2 Example");

	// Setup GLUT display function
	// We will also call ImGui_ImplGLUT_InstallFuncs() to get all the other functions installed for us,
	// otherwise it is possible to install our own functions and call the imgui_impl_glut.h functions ourselves.
	glutDisplayFunc(glut_display_func);

	// Setup Dear ImGui context
	IMGUI_CHECKVERSION();
	ImGui::CreateContext();
	ImGuiIO& io = ImGui::GetIO(); (void)io;
	//io.ConfigFlags \|= ImGuiConfigFlags_NavEnableKeyboard; // Enable Keyboard Controls

	// Setup Dear ImGui style
	ImGui::StyleColorsDark();
	//ImGui::StyleColorsClassic();

	// Setup Platform/Renderer bindings
	ImGui_ImplGLUT_Init();
	ImGui_ImplGLUT_InstallFuncs();
	ImGui_ImplOpenGL2_Init();

	// Load Fonts
	// - If no fonts are loaded, dear imgui will use the default font. You can also load multiple fonts and use ImGui::PushFont()/PopFont() to select them.
	// - AddFontFromFileTTF() will return the ImFont* so you can store it if you need to select the font among multiple.
	// - If the file cannot be loaded, the function will return NULL. Please handle those errors in your application (e.g. use an assertion, or display an error and quit).
	// - The fonts will be rasterized at a given size (w/ oversampling) and stored into a texture when calling ImFontAtlas::Build()/GetTexDataAsXXXX(), which ImGui_ImplXXXX_NewFrame below will call.
	// - Read 'docs/FONTS.md' for more instructions and details.
	// - Remember that in C/C++ if you want to include a backslash \ in a string literal you need to write a double backslash \\ !
	//io.Fonts->AddFontDefault();
	//io.Fonts->AddFontFromFileTTF("../../misc/fonts/Roboto-Medium.ttf", 16.0f);
	//io.Fonts->AddFontFromFileTTF("../../misc/fonts/Cousine-Regular.ttf", 15.0f);
	//io.Fonts->AddFontFromFileTTF("../../misc/fonts/DroidSans.ttf", 16.0f);
	//io.Fonts->AddFontFromFileTTF("../../misc/fonts/ProggyTiny.ttf", 10.0f);
	//ImFont* font = io.Fonts->AddFontFromFileTTF("c:\\Windows\\Fonts\\ArialUni.ttf", 18.0f, NULL, io.Fonts->GetGlyphRangesJapanese());
	//IM_ASSERT(font != NULL);

	glutMainLoop();

	// Cleanup
	ImGui_ImplOpenGL2_Shutdown();
	ImGui_ImplGLUT_Shutdown();
	ImGui::DestroyContext();

	return 0;
	}