imgui/examples/opengl_example/imgui_impl_glfw.cpp

// ImGui GLFW bindings
// https://github.com/ocornut/imgui

#include <imgui.h>
#include "imgui_impl_glfw.h"

// GLFW
#include <GLFW/glfw3.h>
#ifdef _MSC_VER
#undef APIENTRY
#define GLFW_EXPOSE_NATIVE_WIN32
#define GLFW_EXPOSE_NATIVE_WGL
#include <GLFW/glfw3native.h>
#endif

static GLFWwindow*  GWindow = NULL;
static bool         GMousePressed[3] = { false, false, false };
static double       GTime = 0.0f;
static bool         GFontTextureLoaded;

// 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)
static void ImGui_ImplGlfw_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);
    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
    #define OFFSETOF(TYPE, ELEMENT) ((size_t)&(((TYPE *)0)->ELEMENT))
    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];
            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;
        }
    }
    #undef OFFSETOF

    // 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();
}

static const char* ImGui_ImplGlfw_GetClipboardText()
{
    return glfwGetClipboardString(GWindow);
}

static void ImGui_ImplGlfw_SetClipboardText(const char* text)
{
    glfwSetClipboardString(GWindow, text);
}

void ImGui_ImplGlfw_MouseButtonCallback(GLFWwindow* window, int button, int action, int mods)
{
    if (action == GLFW_PRESS && button >= 0 && button < 3)
        GMousePressed[button] = true;
}

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

void ImGui_ImplGlFw_KeyCallback(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;
}

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

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

    unsigned char* pixels;
    int width, height;
    io.Fonts->GetTexDataAsAlpha8(&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_LINEAR);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
    glTexImage2D(GL_TEXTURE_2D, 0, GL_ALPHA, width, height, 0, GL_ALPHA, GL_UNSIGNED_BYTE, pixels);

    // Store our identifier
    io.Fonts->TexID = (void *)(intptr_t)tex_id;

    GFontTextureLoaded = true;
}

bool    ImGui_ImplGlfw_Init(GLFWwindow* window, bool install_callbacks)
{
    GWindow = window;

    ImGuiIO& io = ImGui::GetIO();
    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 = ImGui_ImplGlfw_RenderDrawLists;
    io.SetClipboardTextFn = ImGui_ImplGlfw_SetClipboardText;
    io.GetClipboardTextFn = ImGui_ImplGlfw_GetClipboardText;
#ifdef _MSC_VER
    io.ImeWindowHandle = glfwGetWin32Window(GWindow);
#endif

    if (install_callbacks)
    {
        glfwSetMouseButtonCallback(window, ImGui_ImplGlfw_MouseButtonCallback);
        glfwSetScrollCallback(window, ImGui_ImplGlfw_ScrollCallback);
        glfwSetKeyCallback(window, ImGui_ImplGlFw_KeyCallback);
        glfwSetCharCallback(window, ImGui_ImplGlfw_CharCallback);
    }

    return true;
}

void ImGui_ImplGlfw_Shutdown()
{
    GLuint tex_id = (GLuint)ImGui::GetIO().Fonts->TexID;
    if (tex_id)
    {
        glDeleteTextures(1, &tex_id);
        ImGui::GetIO().Fonts->TexID = 0;
    }
    ImGui::Shutdown();
}

void ImGui_ImplGlfw_NewFrame()
{
    if (!GFontTextureLoaded)
        ImGui_ImplGlfw_LoadFontsTexture();

    ImGuiIO& io = ImGui::GetIO();

    // Setup display size (every frame to accommodate for window resizing)
    int w, h;
    int display_w, display_h;
    glfwGetWindowSize(GWindow, &w, &h);
    glfwGetFramebufferSize(GWindow, &display_w, &display_h);
    io.DisplaySize = ImVec2((float)display_w, (float)display_h);

    // Setup time step
    double current_time =  glfwGetTime();
    io.DeltaTime = GTime > 0.0 ? (float)(current_time - GTime) : (float)(1.0f/60.0f);
    GTime = current_time;

    // Setup inputs
    // (we already got mouse wheel, keyboard keys & characters from glfw callbacks polled in glfwPollEvents())
    double mouse_x, mouse_y;
    glfwGetCursorPos(GWindow, &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] = GMousePressed[0] || glfwGetMouseButton(GWindow, 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] = GMousePressed[1] || glfwGetMouseButton(GWindow, GLFW_MOUSE_BUTTON_RIGHT) != 0;
    io.MouseDown[2] = GMousePressed[2] || glfwGetMouseButton(GWindow, GLFW_MOUSE_BUTTON_MIDDLE) != 0;
    GMousePressed[0] = false;
    GMousePressed[1] = false;
    GMousePressed[2] = false;

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