imgui/examples/opengl3_example/main.cpp

// ImGui - standalone example application for OpenGL 3, using programmable pipeline

#ifdef _MSC_VER
#pragma warning (disable: 4996)                        // 'This function or variable may be unsafe': strcpy, strdup, sprintf, vsnprintf, sscanf, fopen
#endif
#ifdef __clang__
#pragma clang diagnostic ignored "-Wunused-function"   // warning: unused function
#endif

#include "../../imgui.h"
#include <stdio.h>

// 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 bool mousePressed[2] = { false, false };

// Shader variables
static int shader_handle, vert_handle, frag_handle;
static int texture_location, proj_mtx_location;
static int position_location, uv_location, colour_location;
static size_t vbo_max_size = 20000;
static unsigned int vbo_handle, vao_handle;

// 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:
// - try adjusting ImGui::GetIO().PixelCenterOffset to 0.0f or 0.5f
// - in your Render function, try translating your projection matrix by (0.5f,0.5f) or (0.375f,0.375f)
static void ImImpl_RenderDrawLists(ImDrawList** const cmd_lists, int cmd_lists_count)
{
    if (cmd_lists_count == 0)
        return;

    // Setup render state: alpha-blending enabled, no face culling, no depth testing, scissor enabled
    glEnable(GL_BLEND);
    glBlendEquation(GL_FUNC_ADD);
    glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
    glDisable(GL_CULL_FACE);
    glDisable(GL_DEPTH_TEST);
    glEnable(GL_SCISSOR_TEST);
    glActiveTexture(GL_TEXTURE0);

    // Setup orthographic projection matrix
    const float width = ImGui::GetIO().DisplaySize.x;
    const float height = ImGui::GetIO().DisplaySize.y;
    const float ortho_projection[4][4] =
    {
        { 2.0f/width,	0.0f,			0.0f,		0.0f },
        { 0.0f,			2.0f/-height,	0.0f,		0.0f },
        { 0.0f,			0.0f,			-1.0f,		0.0f },
        { -1.0f,		1.0f,			0.0f,		1.0f },
    };
    glUseProgram(shader_handle);
    glUniform1i(texture_location, 0);
    glUniformMatrix4fv(proj_mtx_location, 1, GL_FALSE, &ortho_projection[0][0]);

    // Grow our buffer according to what we need
    size_t total_vtx_count = 0;
    for (int n = 0; n < cmd_lists_count; n++)
        total_vtx_count += cmd_lists[n]->vtx_buffer.size();
    glBindBuffer(GL_ARRAY_BUFFER, vbo_handle);
    size_t neededBufferSize = total_vtx_count * sizeof(ImDrawVert);
    if (neededBufferSize > vbo_max_size)
    {
        vbo_max_size = neededBufferSize + 5000;  // Grow buffer
        glBufferData(GL_ARRAY_BUFFER, vbo_max_size, NULL, GL_STREAM_DRAW);
    }

    // Copy and convert all vertices into a single contiguous buffer
    unsigned char* buffer_data = (unsigned char*)glMapBuffer(GL_ARRAY_BUFFER, GL_WRITE_ONLY);
    if (!buffer_data)
        return;
    for (int n = 0; n < cmd_lists_count; n++)
    {
        const ImDrawList* cmd_list = cmd_lists[n];
        memcpy(buffer_data, &cmd_list->vtx_buffer[0], cmd_list->vtx_buffer.size() * sizeof(ImDrawVert));
        buffer_data += cmd_list->vtx_buffer.size() * sizeof(ImDrawVert);
    }
    glUnmapBuffer(GL_ARRAY_BUFFER);
    glBindBuffer(GL_ARRAY_BUFFER, 0);
    glBindVertexArray(vao_handle);

    int cmd_offset = 0;
    for (int n = 0; n < cmd_lists_count; n++)
    {
        const ImDrawList* cmd_list = cmd_lists[n];
        int vtx_offset = cmd_offset;
        const ImDrawCmd* pcmd_end = cmd_list->commands.end();
        for (const ImDrawCmd* pcmd = cmd_list->commands.begin(); pcmd != pcmd_end; pcmd++)
        {
            glBindTexture(GL_TEXTURE_2D, (GLuint)(intptr_t)pcmd->texture_id);
            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;
        }
        cmd_offset = vtx_offset;
    }

    // Restore modified state
    glBindVertexArray(0);
    glUseProgram(0);
    glDisable(GL_SCISSOR_TEST);
    glBindTexture(GL_TEXTURE_2D, 0);
}

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);
}

void InitGL()
{
    glfwSetErrorCallback(glfw_error_callback);
    if (!glfwInit())
        exit(1);

    glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
    glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
    glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);

    window = glfwCreateWindow(1280, 720, "ImGui OpenGL3 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);

    glewExperimental = GL_TRUE;

    GLenum err = glewInit();
    if (GLEW_OK != err)
        fprintf(stderr, "Error: %s\n", glewGetErrorString(err));

    const GLchar *vertex_shader =
        "#version 330\n"
        "uniform mat4 ProjMtx;\n"
        "in vec2 Position;\n"
        "in vec2 UV;\n"
        "in vec4 Color;\n"
        "out vec2 Frag_UV;\n"
        "out vec4 Frag_Color;\n"
        "void main()\n"
        "{\n"
        "	Frag_UV = UV;\n"
        "	Frag_Color = Color;\n"
        "	gl_Position = ProjMtx * vec4(Position.xy,0,1);\n"
        "}\n";

    const GLchar* fragment_shader =
        "#version 330\n"
        "uniform sampler2D Texture;\n"
        "in vec2 Frag_UV;\n"
        "in vec4 Frag_Color;\n"
        "out vec4 Out_Color;\n"
        "void main()\n"
        "{\n"
        "	Out_Color = Frag_Color * texture( Texture, Frag_UV.st);\n"
        "}\n";

    shader_handle = glCreateProgram();
    vert_handle = glCreateShader(GL_VERTEX_SHADER);
    frag_handle = glCreateShader(GL_FRAGMENT_SHADER);
    glShaderSource(vert_handle, 1, &vertex_shader, 0);
    glShaderSource(frag_handle, 1, &fragment_shader, 0);
    glCompileShader(vert_handle);
    glCompileShader(frag_handle);
    glAttachShader(shader_handle, vert_handle);
    glAttachShader(shader_handle, frag_handle);
    glLinkProgram(shader_handle);

    texture_location = glGetUniformLocation(shader_handle, "Texture");
    proj_mtx_location = glGetUniformLocation(shader_handle, "ProjMtx");
    position_location = glGetAttribLocation(shader_handle, "Position");
    uv_location = glGetAttribLocation(shader_handle, "UV");
    colour_location = glGetAttribLocation(shader_handle, "Color");

    glGenBuffers(1, &vbo_handle);
    glBindBuffer(GL_ARRAY_BUFFER, vbo_handle);
    glBufferData(GL_ARRAY_BUFFER, vbo_max_size, NULL, GL_DYNAMIC_DRAW);

    glGenVertexArrays(1, &vao_handle);
    glBindVertexArray(vao_handle);
    glBindBuffer(GL_ARRAY_BUFFER, vbo_handle);
    glEnableVertexAttribArray(position_location);
    glEnableVertexAttribArray(uv_location);
    glEnableVertexAttribArray(colour_location);

    glVertexAttribPointer(position_location, 2, GL_FLOAT, GL_FALSE, sizeof(ImDrawVert), (GLvoid*)OFFSETOF(ImDrawVert, pos));
    glVertexAttribPointer(uv_location, 2, GL_FLOAT, GL_FALSE, sizeof(ImDrawVert), (GLvoid*)OFFSETOF(ImDrawVert, uv));
    glVertexAttribPointer(colour_location, 4, GL_UNSIGNED_BYTE, GL_TRUE, sizeof(ImDrawVert), (GLvoid*)OFFSETOF(ImDrawVert, col));
    glBindVertexArray(0);
    glBindBuffer(GL_ARRAY_BUFFER, 0);
}

void LoadFontTexture(ImFont* font)
{
    unsigned char* pixels;
    int width, height;
    font->GetTextureDataRGBA32(&pixels, &width, &height);

    GLuint tex_id;
    glGenTextures(1, &tex_id);
    glBindTexture(GL_TEXTURE_2D, tex_id);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, width, height, 0, GL_RGBA, GL_UNSIGNED_BYTE, pixels);

    font->TexID = (void *)(intptr_t)tex_id;
}

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 timestep is variable)
    io.PixelCenterOffset = 0.5f;                                  // 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 (optionally load a custom TTF font)
    //io.Font->LoadFromFileTTF("myfont.ttf", font_size_px, ImFont::GetGlyphRangesDefault());
    //io.Font->DisplayOffset.y += 1.0f;
    LoadFontTexture(io.Font);
}

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();

    bool show_test_window = true;
    bool show_another_window = false;
    ImVec4 clear_col(0.8f, 0.6f, 0.6f, 1.0f);

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

        // 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);
            ImGui::ColorEdit3("clear color", (float*)&clear_col);
            if (ImGui::Button("Test Window")) show_test_window ^= 1;
            if (ImGui::Button("Another Window")) show_another_window ^= 1;

            // 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(clear_col.x, clear_col.y, clear_col.z, clear_col.w);
        glClear(GL_COLOR_BUFFER_BIT);
        ImGui::Render();
        glfwSwapBuffers(window);
    }

    // Cleanup
    if (vao_handle) glDeleteVertexArrays(1, &vao_handle);
    if (vbo_handle) glDeleteBuffers(1, &vbo_handle);
    glDetachShader(shader_handle, vert_handle);
    glDetachShader(shader_handle, frag_handle);
    glDeleteShader(vert_handle);
    glDeleteShader(frag_handle);
    glDeleteProgram(shader_handle);

    ImGui::Shutdown();
    glfwTerminate();

    return 0;
}