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// Dear ImGui: standalone example application for Emscripten, using SDL2 + OpenGL3
// (Emscripten is a C++-to-javascript compiler, used to publish executables for the web. See
// If you are new to Dear ImGui, read documentation from the docs/ folder + read the top of imgui.cpp.
// Read online:
// This is mostly the same code as the SDL2 + 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 as an example on how to do just that.
#include "imgui.h"
#include "imgui_impl_sdl.h"
#include "imgui_impl_opengl3.h"
#include <stdio.h>
#include <emscripten.h>
#include <SDL.h>
#include <SDL_opengles2.h>
// Emscripten requires to have full control over the main loop. We're going to store our SDL 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.
SDL_Window* g_Window = NULL;
SDL_GLContext g_GLContext = NULL;
// For clarity, our main loop code is declared at the end.
void main_loop(void*);
int main(int, char**)
// Setup SDL
printf("Error: %s\n", SDL_GetError());
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";
//const char* glsl_version = "#version 300 es";
// Create window with graphics context
SDL_GL_SetAttribute(SDL_GL_DEPTH_SIZE, 24);
SDL_DisplayMode current;
SDL_GetCurrentDisplayMode(0, &current);
g_Window = SDL_CreateWindow("Dear ImGui Emscripten example", SDL_WINDOWPOS_CENTERED, SDL_WINDOWPOS_CENTERED, 1280, 720, window_flags);
g_GLContext = SDL_GL_CreateContext(g_Window);
if (!g_GLContext)
fprintf(stderr, "Failed to initialize WebGL context!\n");
return 1;
SDL_GL_SetSwapInterval(1); // Enable vsync
// Setup Dear ImGui context
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
// Setup Platform/Renderer backends
ImGui_ImplSDL2_InitForOpenGL(g_Window, g_GLContext);
// 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/' 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->AddFontFromFileTTF("fonts/Roboto-Medium.ttf", 16.0f);
//io.Fonts->AddFontFromFileTTF("fonts/Cousine-Regular.ttf", 15.0f);
//io.Fonts->AddFontFromFileTTF("fonts/DroidSans.ttf", 16.0f);
//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);
// 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);
void main_loop(void* arg)
ImGuiIO& io = ImGui::GetIO();
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.
// - 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.
SDL_Event event;
while (SDL_PollEvent(&event))
// Capture events here, based on io.WantCaptureMouse and io.WantCaptureKeyboard
// Start the Dear ImGui frame
// 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)
// 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)
ImGui::Text("counter = %d", counter);
ImGui::Text("Application average %.3f ms/frame (%.1f FPS)", 1000.0f / ImGui::GetIO().Framerate, ImGui::GetIO().Framerate);
// 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;
// Rendering
SDL_GL_MakeCurrent(g_Window, g_GLContext);
glViewport(0, 0, (int)io.DisplaySize.x, (int)io.DisplaySize.y);
glClearColor(clear_color.x, clear_color.y, clear_color.z, clear_color.w);