examples/opengl_example/main.cpp

// ImGui - standalone example application for OpenGL 2, using fixed pipeline

#ifdef _MSC_VER
#pragma warning (disable: 4996)         // 'This function or variable may be unsafe': strcpy, strdup, sprintf, vsnprintf, sscanf, fopen
#endif

#include "../../imgui.h"
#define STB_IMAGE_IMPLEMENTATION
#include "../shared/stb_image.h"        // stb_image.h for PNG loading

// Glfw/Glew
#define GLEW_STATIC
#include <GL/glew.h>
#include <GLFW/glfw3.h>
#define OFFSETOF(TYPE, ELEMENT) ((size_t)&(((TYPE *)0)->ELEMENT))

static GLFWwindow* window;
static GLuint fontTex;
static bool mousePressed[2] = { false, false };

// This is the main rendering function that you have to implement and provide to ImGui (via setting up 'RenderDrawListsFn' in the ImGuiIO structure)
// If text or lines are blurry when integrating ImGui in your engine:
// - in your Render function, try translating your projection matrix by (0.5f,0.5f) or (0.375f,0.375f)
// - try adjusting ImGui::GetIO().PixelCenterOffset to 0.5f or 0.375f
static void ImImpl_RenderDrawLists(ImDrawList** const cmd_lists, int cmd_lists_count)
{
    if (cmd_lists_count == 0)
        return;

    // We are using the OpenGL fixed pipeline to make the example code simpler to read!
    // A probable faster way to render would be to collate all vertices from all cmd_lists into a single vertex buffer.
    // Setup render state: alpha-blending enabled, no face culling, no depth testing, scissor enabled, vertex/texcoord/color pointers.
    glPushAttrib(GL_ENABLE_BIT | GL_COLOR_BUFFER_BIT | GL_TRANSFORM_BIT);
    glEnable(GL_BLEND);
    glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
    glDisable(GL_CULL_FACE);
    glDisable(GL_DEPTH_TEST);
    glEnable(GL_SCISSOR_TEST);
    glEnableClientState(GL_VERTEX_ARRAY);
    glEnableClientState(GL_TEXTURE_COORD_ARRAY);
    glEnableClientState(GL_COLOR_ARRAY);

    // Setup texture
    glBindTexture(GL_TEXTURE_2D, fontTex);
    glEnable(GL_TEXTURE_2D);

    // Setup orthographic projection matrix
    const float width = ImGui::GetIO().DisplaySize.x;
    const float height = ImGui::GetIO().DisplaySize.y;
    glMatrixMode(GL_PROJECTION);
    glPushMatrix();
    glLoadIdentity();
    glOrtho(0.0f, width, height, 0.0f, -1.0f, +1.0f);
    glMatrixMode(GL_MODELVIEW);
    glPushMatrix();
    glLoadIdentity();

    // Render command lists
    for (int n = 0; n < cmd_lists_count; n++)
    {
        const ImDrawList* cmd_list = cmd_lists[n];
        const unsigned char* vtx_buffer = (const unsigned char*)&cmd_list->vtx_buffer.front();
        glVertexPointer(2, GL_FLOAT, sizeof(ImDrawVert), (void*)(vtx_buffer + OFFSETOF(ImDrawVert, pos)));
        glTexCoordPointer(2, GL_FLOAT, sizeof(ImDrawVert), (void*)(vtx_buffer + OFFSETOF(ImDrawVert, uv)));
        glColorPointer(4, GL_UNSIGNED_BYTE, sizeof(ImDrawVert), (void*)(vtx_buffer + OFFSETOF(ImDrawVert, col)));

        int vtx_offset = 0;
        for (size_t cmd_i = 0; cmd_i < cmd_list->commands.size(); cmd_i++)
        {
            const ImDrawCmd* pcmd = &cmd_list->commands[cmd_i];
            glScissor((int)pcmd->clip_rect.x, (int)(height - pcmd->clip_rect.w), (int)(pcmd->clip_rect.z - pcmd->clip_rect.x), (int)(pcmd->clip_rect.w - pcmd->clip_rect.y));
            glDrawArrays(GL_TRIANGLES, vtx_offset, pcmd->vtx_count);
            vtx_offset += pcmd->vtx_count;
        }
    }

    // Restore modified state
    glDisableClientState(GL_COLOR_ARRAY);
    glDisableClientState(GL_TEXTURE_COORD_ARRAY);
    glDisableClientState(GL_VERTEX_ARRAY);
    glMatrixMode(GL_MODELVIEW);
    glPopMatrix();
    glMatrixMode(GL_PROJECTION);
    glPopMatrix();
    glPopAttrib();
}

// NB: ImGui already provide OS clipboard support for Windows so this isn't needed if you are using Windows only.
static const char* ImImpl_GetClipboardTextFn()
{
    return glfwGetClipboardString(window);
}

static void ImImpl_SetClipboardTextFn(const char* text)
{
    glfwSetClipboardString(window, text);
}

// GLFW callbacks to get events
static void glfw_error_callback(int error, const char* description)
{
    fputs(description, stderr);
}

static void glfw_mouse_button_callback(GLFWwindow* window, int button, int action, int mods)
{
    if (action == GLFW_PRESS && button >= 0 && button < 2)
        mousePressed[button] = true;
}

static void glfw_scroll_callback(GLFWwindow* window, double xoffset, double yoffset)
{
    ImGuiIO& io = ImGui::GetIO();
    io.MouseWheel += (float)yoffset; // Use fractional mouse wheel, 1.0 unit 5 lines.
}

static void glfw_key_callback(GLFWwindow* window, int key, int scancode, int action, int mods)
{
    ImGuiIO& io = ImGui::GetIO();
    if (action == GLFW_PRESS)
        io.KeysDown[key] = true;
    if (action == GLFW_RELEASE)
        io.KeysDown[key] = false;
    io.KeyCtrl = (mods & GLFW_MOD_CONTROL) != 0;
    io.KeyShift = (mods & GLFW_MOD_SHIFT) != 0;
}

static void glfw_char_callback(GLFWwindow* window, unsigned int c)
{
    if (c > 0 && c < 0x10000)
        ImGui::GetIO().AddInputCharacter((unsigned short)c);
}

// OpenGL code based on http://open.gl tutorials
void InitGL()
{
    glfwSetErrorCallback(glfw_error_callback);

    if (!glfwInit())
        exit(1);

    window = glfwCreateWindow(1280, 720, "ImGui OpenGL example", NULL, NULL);
    glfwMakeContextCurrent(window);
    glfwSetKeyCallback(window, glfw_key_callback);
    glfwSetMouseButtonCallback(window, glfw_mouse_button_callback);
    glfwSetScrollCallback(window, glfw_scroll_callback);
    glfwSetCharCallback(window, glfw_char_callback);

    glewInit();
}

void InitImGui()
{
    ImGuiIO& io = ImGui::GetIO();
    io.DeltaTime = 1.0f/60.0f;                                    // Time elapsed since last frame, in seconds (in this sample app we'll override this every frame because our time step is variable)
    io.PixelCenterOffset = 0.0f;                                  // Align OpenGL texels
    io.KeyMap[ImGuiKey_Tab] = GLFW_KEY_TAB;                       // Keyboard mapping. ImGui will use those indices to peek into the io.KeyDown[] array.
    io.KeyMap[ImGuiKey_LeftArrow] = GLFW_KEY_LEFT;
    io.KeyMap[ImGuiKey_RightArrow] = GLFW_KEY_RIGHT;
    io.KeyMap[ImGuiKey_UpArrow] = GLFW_KEY_UP;
    io.KeyMap[ImGuiKey_DownArrow] = GLFW_KEY_DOWN;
    io.KeyMap[ImGuiKey_Home] = GLFW_KEY_HOME;
    io.KeyMap[ImGuiKey_End] = GLFW_KEY_END;
    io.KeyMap[ImGuiKey_Delete] = GLFW_KEY_DELETE;
    io.KeyMap[ImGuiKey_Backspace] = GLFW_KEY_BACKSPACE;
    io.KeyMap[ImGuiKey_Enter] = GLFW_KEY_ENTER;
    io.KeyMap[ImGuiKey_Escape] = GLFW_KEY_ESCAPE;
    io.KeyMap[ImGuiKey_A] = GLFW_KEY_A;
    io.KeyMap[ImGuiKey_C] = GLFW_KEY_C;
    io.KeyMap[ImGuiKey_V] = GLFW_KEY_V;
    io.KeyMap[ImGuiKey_X] = GLFW_KEY_X;
    io.KeyMap[ImGuiKey_Y] = GLFW_KEY_Y;
    io.KeyMap[ImGuiKey_Z] = GLFW_KEY_Z;

    io.RenderDrawListsFn = ImImpl_RenderDrawLists;
    io.SetClipboardTextFn = ImImpl_SetClipboardTextFn;
    io.GetClipboardTextFn = ImImpl_GetClipboardTextFn;

    // Load font texture
    glGenTextures(1, &fontTex);
    glBindTexture(GL_TEXTURE_2D, fontTex);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);

#if 1
    // Default font (embedded in code)
    const void* png_data;
    unsigned int png_size;
    ImGui::GetDefaultFontData(NULL, NULL, &png_data, &png_size);
    int tex_x, tex_y, tex_comp;
    void* tex_data = stbi_load_from_memory((const unsigned char*)png_data, (int)png_size, &tex_x, &tex_y, &tex_comp, 0);
    IM_ASSERT(tex_data != NULL);
#else
    // Custom font from filesystem
    io.Font = new ImFont();
    io.Font->LoadFromFile("../../extra_fonts/mplus-2m-medium_18.fnt");
    IM_ASSERT(io.Font->IsLoaded());

    int tex_x, tex_y, tex_comp;
    void* tex_data = stbi_load("../../extra_fonts/mplus-2m-medium_18.png", &tex_x, &tex_y, &tex_comp, 0);
    IM_ASSERT(tex_data != NULL);
    
    // Automatically find white pixel from the texture we just loaded
    // (io.Font->TexUvForWhite needs to contains UV coordinates pointing to a white pixel in order to render solid objects)
    for (int tex_data_off = 0; tex_data_off < tex_x*tex_y; tex_data_off++)
        if (((unsigned int*)tex_data)[tex_data_off] == 0xffffffff)
        {
            io.Font->TexUvForWhite = ImVec2((float)(tex_data_off % tex_x)/(tex_x), (float)(tex_data_off / tex_x)/(tex_y));
            break;
        }
#endif

    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, tex_x, tex_y, 0, GL_RGBA, GL_UNSIGNED_BYTE, tex_data);
    stbi_image_free(tex_data);
}

void UpdateImGui()
{
    ImGuiIO& io = ImGui::GetIO();

    // Setup resolution (every frame to accommodate for window resizing)
    int w, h;
    int display_w, display_h;
    glfwGetWindowSize(window, &w, &h);
    glfwGetFramebufferSize(window, &display_w, &display_h);
    io.DisplaySize = ImVec2((float)display_w, (float)display_h);                                   // Display size, in pixels. For clamping windows positions.

    // Setup time step
    static double time = 0.0f;
    const double current_time =  glfwGetTime();
    io.DeltaTime = (float)(current_time - time);
    time = current_time;

    // Setup inputs
    // (we already got mouse wheel, keyboard keys & characters from glfw callbacks polled in glfwPollEvents())
    double mouse_x, mouse_y;
    glfwGetCursorPos(window, &mouse_x, &mouse_y);
    mouse_x *= (float)display_w / w;                                                               // Convert mouse coordinates to pixels
    mouse_y *= (float)display_h / h;
    io.MousePos = ImVec2((float)mouse_x, (float)mouse_y);                                          // Mouse position, in pixels (set to -1,-1 if no mouse / on another screen, etc.)
    io.MouseDown[0] = mousePressed[0] || glfwGetMouseButton(window, GLFW_MOUSE_BUTTON_LEFT) != 0;  // If a mouse press event came, always pass it as "mouse held this frame", so we don't miss click-release events that are shorter than 1 frame.
    io.MouseDown[1] = mousePressed[1] || glfwGetMouseButton(window, GLFW_MOUSE_BUTTON_RIGHT) != 0;

    // Start the frame
    ImGui::NewFrame();
}

// Application code
int main(int argc, char** argv)
{
    InitGL();
    InitImGui();

    while (!glfwWindowShouldClose(window))
    {
        ImGuiIO& io = ImGui::GetIO();
        mousePressed[0] = mousePressed[1] = false;
        glfwPollEvents();
        UpdateImGui();

        static bool show_test_window = true;
        static bool show_another_window = false;

        // 1. Show a simple window
        // Tip: if we don't call ImGui::Begin()/ImGui::End() the widgets appears in a window automatically called "Debug"
        {
            static float f;
            ImGui::Text("Hello, world!");
            ImGui::SliderFloat("float", &f, 0.0f, 1.0f);
            show_test_window ^= ImGui::Button("Test Window");
            show_another_window ^= ImGui::Button("Another Window");

            // Calculate and show frame rate
            static float ms_per_frame[120] = { 0 };
            static int ms_per_frame_idx = 0;
            static float ms_per_frame_accum = 0.0f;
            ms_per_frame_accum -= ms_per_frame[ms_per_frame_idx];
            ms_per_frame[ms_per_frame_idx] = ImGui::GetIO().DeltaTime * 1000.0f;
            ms_per_frame_accum += ms_per_frame[ms_per_frame_idx];
            ms_per_frame_idx = (ms_per_frame_idx + 1) % 120;
            const float ms_per_frame_avg = ms_per_frame_accum / 120;
            ImGui::Text("Application average %.3f ms/frame (%.1f FPS)", ms_per_frame_avg, 1000.0f / ms_per_frame_avg);
        }

        // 2. Show another simple window, this time using an explicit Begin/End pair
        if (show_another_window)
        {
            ImGui::Begin("Another Window", &show_another_window, ImVec2(200,100));
            ImGui::Text("Hello");
            ImGui::End();
        }

        // 3. Show the ImGui test window. Most of the sample code is in ImGui::ShowTestWindow()
        if (show_test_window)
        {
            ImGui::SetNextWindowPos(ImVec2(650, 20), ImGuiSetCondition_FirstUseEver);
            ImGui::ShowTestWindow(&show_test_window);
        }

        // Rendering
        glViewport(0, 0, (int)io.DisplaySize.x, (int)io.DisplaySize.y);
        glClearColor(0.8f, 0.6f, 0.6f, 1.0f);
        glClear(GL_COLOR_BUFFER_BIT);
        ImGui::Render();
        glfwSwapBuffers(window);
    }

    // Cleanup
    ImGui::Shutdown();
    glfwTerminate();

    return 0;
}