imgui/examples/example_emscripten_glfw_opengl3/main.cpp

// Dear ImGui: standalone example application for Emscripten, using GLFW + OpenGL3
// (Emscripten is a C++-to-javascript compiler, used to publish executables for the web. See https://emscripten.org/)
// If you are new to Dear ImGui, read documentation from the docs/ folder + read the top of imgui.cpp.
// Read online: https://github.com/ocornut/imgui/tree/master/docs

// This is mostly the same code as the GLFW + OpenGL3 example, simply with the modifications needed to run on Emscripten.
// It is possible to combine both code into a single source file that will compile properly on Desktop and using Emscripten.
// See https://github.com/ocornut/imgui/pull/2492 as an example on how to do just that.

#include "imgui.h"
#include "imgui_impl_glfw.h"
#include "imgui_impl_opengl3.h"
#include <stdio.h>
#include <emscripten.h>
#define GL_SILENCE_DEPRECATION
#if defined(IMGUI_IMPL_OPENGL_ES2)
#include <GLES2/gl2.h>
#endif
#include <GLFW/glfw3.h> // Will drag system OpenGL headers

// Emscripten requires to have full control over the main loop. We're going to store our GLFW book-keeping variables globally.
// Having a single function that acts as a loop prevents us to store state in the stack of said function. So we need some location for this.
GLFWwindow*     g_Window = NULL;

static void glfw_error_callback(int error, const char* description)
{
    fprintf(stderr, "Glfw Error %d: %s\n", error, description);
}

// For clarity, our main loop code is declared at the end.
static void main_loop(void*);

int main(int, char**)
{
    // Setup window
    glfwSetErrorCallback(glfw_error_callback);
    if (!glfwInit())
        return 1;

    // For the browser using Emscripten, we are going to use WebGL1 with GL ES2. See the Makefile. for requirement details.
    // It is very likely the generated file won't work in many browsers. Firefox is the only sure bet, but I have successfully
    // run this code on Chrome for Android for example.
    const char* glsl_version = "#version 100";
    glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 2);
    glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 0);
    glfwWindowHint(GLFW_CLIENT_API, GLFW_OPENGL_ES_API);

    // Create window with graphics context
    GLFWwindow* window = glfwCreateWindow(1280, 720, "Dear ImGui GLFW+Emscripten example", NULL, NULL);
    if (window == NULL)
        return 1;
    glfwMakeContextCurrent(window);
    glfwSwapInterval(1); // Enable vsync
    g_Window = window;

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

    // For an Emscripten build we are disabling file-system access, so let's not attempt to do a fopen() of the imgui.ini file.
    // You may manually call LoadIniSettingsFromMemory() to load settings from your own storage.
    io.IniFilename = NULL;

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

    // Setup Platform/Renderer backends
    ImGui_ImplGlfw_InitForOpenGL(window, true);
    ImGui_ImplOpenGL3_Init(glsl_version);

    // 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.
    // - Use '#define IMGUI_ENABLE_FREETYPE' in your imconfig file to use Freetype for higher quality font rendering.
    // - 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 \\ !
    // - Emscripten allows preloading a file or folder to be accessible at runtime. See Makefile for details.
    //io.Fonts->AddFontDefault();
#ifndef IMGUI_DISABLE_FILE_FUNCTIONS
    //io.Fonts->AddFontFromFileTTF("fonts/segoeui.ttf", 18.0f);
    io.Fonts->AddFontFromFileTTF("fonts/DroidSans.ttf", 16.0f);
    //io.Fonts->AddFontFromFileTTF("fonts/Roboto-Medium.ttf", 16.0f);
    //io.Fonts->AddFontFromFileTTF("fonts/Cousine-Regular.ttf", 15.0f);
    //io.Fonts->AddFontFromFileTTF("fonts/ProggyTiny.ttf", 10.0f);
    //ImFont* font = io.Fonts->AddFontFromFileTTF("fonts/ArialUni.ttf", 18.0f, NULL, io.Fonts->GetGlyphRangesJapanese());
    //IM_ASSERT(font != NULL);
#endif

    // This function call won't return, and will engage in an infinite loop, processing events from the browser, and dispatching them.
    emscripten_set_main_loop_arg(main_loop, NULL, 0, true);
}

static void main_loop(void* arg)
{
    IM_UNUSED(arg); // We can pass this argument as the second parameter of emscripten_set_main_loop_arg(), but we don't use that.

    // Our state (make them static = more or less global) as a convenience to keep the example terse.
    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);

    // Poll and handle events (inputs, window resize, etc.)
    // 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, or clear/overwrite your copy of the mouse data.
    // - When io.WantCaptureKeyboard is true, do not dispatch keyboard input data to your main application, or clear/overwrite your copy of the keyboard data.
    // Generally you may always pass all inputs to dear imgui, and hide them from your application based on those two flags.
    glfwPollEvents();

    // Start the Dear ImGui frame
    ImGui_ImplOpenGL3_NewFrame();
    ImGui_ImplGlfw_NewFrame();
    ImGui::NewFrame();

    // 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 create 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();
    }

    // Rendering
    ImGui::Render();
    int display_w, display_h;
    glfwGetFramebufferSize(g_Window, &display_w, &display_h);
    glViewport(0, 0, display_w, display_h);
    glClearColor(clear_color.x * clear_color.w, clear_color.y * clear_color.w, clear_color.z * clear_color.w, clear_color.w);
    glClear(GL_COLOR_BUFFER_BIT);
    ImGui_ImplOpenGL3_RenderDrawData(ImGui::GetDrawData());

    glfwSwapBuffers(g_Window);
}