imgui/examples/sdl_opengl_example/imgui_impl_sdl.cpp

// ImGui SDL2 binding with OpenGL
// https://github.com/ocornut/imgui

#include <SDL.h>
#include <SDL_syswm.h>
#include <SDL_opengl.h>
#include <imgui.h>
#include "imgui_impl_sdl.h"

// Data
static double       g_Time = 0.0f;
static bool         g_MousePressed[3] = { false, false, false };
static float        g_MouseWheel = 0.0f;
static GLuint       g_FontTexture = 0;

// 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_ImplSdl_RenderDrawLists(ImDrawData* draw_data)
{
    // 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);
    //glUseProgram(0); // You may want this if using this code in an OpenGL 3+ context

    // 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 < draw_data->CmdListsCount; n++)
    {
        const ImDrawList* cmd_list = draw_data->CmdLists[n];
        const unsigned char* vtx_buffer = (const unsigned char*)&cmd_list->VtxBuffer.front();
        const ImDrawIdx* idx_buffer = &cmd_list->IdxBuffer.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)));

        for (int cmd_i = 0; cmd_i < cmd_list->CmdBuffer.size(); cmd_i++)
        {
            const ImDrawCmd* pcmd = &cmd_list->CmdBuffer[cmd_i];
            if (pcmd->UserCallback)
            {
                pcmd->UserCallback(cmd_list, pcmd);
            }
            else
            {
                glBindTexture(GL_TEXTURE_2D, (GLuint)(intptr_t)pcmd->TextureId);
                glScissor((int)pcmd->ClipRect.x, (int)(height - pcmd->ClipRect.w), (int)(pcmd->ClipRect.z - pcmd->ClipRect.x), (int)(pcmd->ClipRect.w - pcmd->ClipRect.y));
                glDrawElements(GL_TRIANGLES, (GLsizei)pcmd->ElemCount, GL_UNSIGNED_SHORT, idx_buffer);
            }
            idx_buffer += pcmd->ElemCount;
        }
    }
    #undef OFFSETOF

    // Restore modified state
    glDisableClientState(GL_COLOR_ARRAY);
    glDisableClientState(GL_TEXTURE_COORD_ARRAY);
    glDisableClientState(GL_VERTEX_ARRAY);
    glBindTexture(GL_TEXTURE_2D, 0);
    glMatrixMode(GL_MODELVIEW);
    glPopMatrix();
    glMatrixMode(GL_PROJECTION);
    glPopMatrix();
    glPopAttrib();
}

static const char* ImGui_ImplSdl_GetClipboardText()
{
	return SDL_GetClipboardText();
}

static void ImGui_ImplSdl_SetClipboardText(const char* text)
{
    SDL_SetClipboardText(text);
}

bool ImGui_ImplSdl_ProcessEvent(SDL_Event* event)
{
    ImGuiIO& io = ImGui::GetIO();
    switch (event->type)
    {
    case SDL_MOUSEWHEEL:
        {
            if (event->wheel.y > 0)
                g_MouseWheel = 1;
            if (event->wheel.y < 0)
                g_MouseWheel = -1;
            return true;
        }
    case SDL_MOUSEBUTTONDOWN:
        {
            if (event->button.button == SDL_BUTTON_LEFT) g_MousePressed[0] = true;
            if (event->button.button == SDL_BUTTON_RIGHT) g_MousePressed[1] = true;
            if (event->button.button == SDL_BUTTON_MIDDLE) g_MousePressed[2] = true;
            return true;
        }
    case SDL_TEXTINPUT:
        {
            ImGuiIO& io = ImGui::GetIO();
            unsigned int c = event->text.text[0];
            if (c > 0 && c < 0x10000)
                io.AddInputCharacter((unsigned short)c);
            return true;
        }
    case SDL_KEYDOWN:
    case SDL_KEYUP:
        {
            int key = event->key.keysym.sym & ~SDLK_SCANCODE_MASK;
            io.KeysDown[key] = (event->type == SDL_KEYDOWN);
            io.KeyShift = ((SDL_GetModState() & KMOD_SHIFT) != 0);
            io.KeyCtrl = ((SDL_GetModState() & KMOD_CTRL) != 0);
            io.KeyAlt = ((SDL_GetModState() & KMOD_ALT) != 0);
            return true;
        }
    }
    return false;
}

bool ImGui_ImplSdl_CreateDeviceObjects()
{
    ImGuiIO& io = ImGui::GetIO();

    // Build texture
    unsigned char* pixels;
    int width, height;
    io.Fonts->GetTexDataAsAlpha8(&pixels, &width, &height);

    // Create texture
    glGenTextures(1, &g_FontTexture);
    glBindTexture(GL_TEXTURE_2D, g_FontTexture);
    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)g_FontTexture;

    // Cleanup (don't clear the input data if you want to append new fonts later)
	io.Fonts->ClearInputData();
	io.Fonts->ClearTexData();

    return true;
}

void    ImGui_ImplSdl_InvalidateDeviceObjects()
{
    if (g_FontTexture)
    {
        glDeleteTextures(1, &g_FontTexture);
        ImGui::GetIO().Fonts->TexID = 0;
        g_FontTexture = 0;
    }
}

bool    ImGui_ImplSdl_Init(SDL_Window *window)
{
    ImGuiIO& io = ImGui::GetIO();
    io.KeyMap[ImGuiKey_Tab] = SDLK_TAB;                 // Keyboard mapping. ImGui will use those indices to peek into the io.KeyDown[] array.
    io.KeyMap[ImGuiKey_LeftArrow] = SDL_SCANCODE_LEFT;
    io.KeyMap[ImGuiKey_RightArrow] = SDL_SCANCODE_RIGHT;
    io.KeyMap[ImGuiKey_UpArrow] = SDL_SCANCODE_UP;
    io.KeyMap[ImGuiKey_DownArrow] = SDL_SCANCODE_DOWN;
    io.KeyMap[ImGuiKey_PageUp] = SDL_SCANCODE_PAGEUP;
    io.KeyMap[ImGuiKey_PageDown] = SDL_SCANCODE_PAGEDOWN;
    io.KeyMap[ImGuiKey_Home] = SDL_SCANCODE_HOME;
    io.KeyMap[ImGuiKey_End] = SDL_SCANCODE_END;
    io.KeyMap[ImGuiKey_Delete] = SDLK_DELETE;
    io.KeyMap[ImGuiKey_Backspace] = SDLK_BACKSPACE;
    io.KeyMap[ImGuiKey_Enter] = SDLK_RETURN;
    io.KeyMap[ImGuiKey_Escape] = SDLK_ESCAPE;
    io.KeyMap[ImGuiKey_A] = SDLK_a;
    io.KeyMap[ImGuiKey_C] = SDLK_c;
    io.KeyMap[ImGuiKey_V] = SDLK_v;
    io.KeyMap[ImGuiKey_X] = SDLK_x;
    io.KeyMap[ImGuiKey_Y] = SDLK_y;
    io.KeyMap[ImGuiKey_Z] = SDLK_z;
	
    io.RenderDrawListsFn = ImGui_ImplSdl_RenderDrawLists;
    io.SetClipboardTextFn = ImGui_ImplSdl_SetClipboardText;
    io.GetClipboardTextFn = ImGui_ImplSdl_GetClipboardText;
	
#ifdef _MSC_VER
	SDL_SysWMinfo wmInfo;
	SDL_VERSION(&wmInfo.version);
	SDL_GetWindowWMInfo(window, &wmInfo);
    io.ImeWindowHandle = wmInfo.info.win.window;
#endif

    return true;
}

void ImGui_ImplSdl_Shutdown()
{
    ImGui_ImplSdl_InvalidateDeviceObjects();
    ImGui::Shutdown();
}

void ImGui_ImplSdl_NewFrame(SDL_Window *window)
{
    if (!g_FontTexture)
        ImGui_ImplSdl_CreateDeviceObjects();

    ImGuiIO& io = ImGui::GetIO();

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

    // Setup time step
	Uint32	time = SDL_GetTicks();
	double current_time = time / 1000.0;
    io.DeltaTime = g_Time > 0.0 ? (float)(current_time - g_Time) : (float)(1.0f/60.0f);
    g_Time = current_time;

    // Setup inputs
    // (we already got mouse wheel, keyboard keys & characters from glfw callbacks polled in glfwPollEvents())
    int mx, my;
    Uint32 mouseMask = SDL_GetMouseState(&mx, &my);
    if (SDL_GetWindowFlags(window) & SDL_WINDOW_MOUSE_FOCUS)
    	io.MousePos = ImVec2((float)mx, (float)my);   // Mouse position, in pixels (set to -1,-1 if no mouse / on another screen, etc.)
    else
    	io.MousePos = ImVec2(-1,-1);
   
	io.MouseDown[0] = g_MousePressed[0] || (mouseMask & SDL_BUTTON(SDL_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] = g_MousePressed[1] || (mouseMask & SDL_BUTTON(SDL_BUTTON_RIGHT)) != 0;
	io.MouseDown[2] = g_MousePressed[2] || (mouseMask & SDL_BUTTON(SDL_BUTTON_MIDDLE)) != 0;
    g_MousePressed[0] = g_MousePressed[1] = g_MousePressed[2] = false;

    io.MouseWheel = g_MouseWheel;
    g_MouseWheel = 0.0f;

    // Hide OS mouse cursor if ImGui is drawing it
    SDL_ShowCursor(io.MouseDrawCursor ? 0 : 1);

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