sdl_v.cpp

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/*
 * This file is part of OpenTTD.
 * OpenTTD is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, version 2.
 * OpenTTD is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
 * See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with OpenTTD. If not, see <http://www.gnu.org/licenses/>.
 */
 
#ifdef WITH_SDL
 
#include "../stdafx.h"
#include "../openttd.h"
#include "../gfx_func.h"
#include "../rev.h"
#include "../blitter/factory.hpp"
#include "../network/network.h"
#include "../thread.h"
#include "../progress.h"
#include "../core/random_func.hpp"
#include "../core/math_func.hpp"
#include "../fileio_func.h"
#include "../framerate_type.h"
#include "sdl_v.h"
#include <SDL.h>
#include <mutex>
#include <condition_variable>
 
#include "../safeguards.h"
 
static FVideoDriver_SDL iFVideoDriver_SDL;
 
static SDL_Surface *_sdl_surface;
static SDL_Surface *_sdl_realscreen;
static bool _all_modes;
 
static bool _draw_threaded;
static std::recursive_mutex *_draw_mutex = nullptr;
static std::condition_variable_any *_draw_signal = nullptr;
static volatile bool _draw_continue;
static Palette _local_palette;
 
#define MAX_DIRTY_RECTS 100
static SDL_Rect _dirty_rects[MAX_DIRTY_RECTS];
static int _num_dirty_rects;
static int _use_hwpalette;
static int _requested_hwpalette; /* Did we request a HWPALETTE for the current video mode? */
 
void VideoDriver_SDL::MakeDirty(int left, int top, int width, int height)
{
  if (_num_dirty_rects < MAX_DIRTY_RECTS) {
    _dirty_rects[_num_dirty_rects].x = left;
    _dirty_rects[_num_dirty_rects].y = top;
    _dirty_rects[_num_dirty_rects].w = width;
    _dirty_rects[_num_dirty_rects].h = height;
  }
  _num_dirty_rects++;
}
 
static void UpdatePalette(bool init = false)
{
  SDL_Color pal[256];
 
  for (int i = 0; i != _local_palette.count_dirty; i++) {
    pal[i].r = _local_palette.palette[_local_palette.first_dirty + i].r;
    pal[i].g = _local_palette.palette[_local_palette.first_dirty + i].g;
    pal[i].b = _local_palette.palette[_local_palette.first_dirty + i].b;
    pal[i].unused = 0;
  }
 
  SDL_SetColors(_sdl_surface, pal, _local_palette.first_dirty, _local_palette.count_dirty);
 
  if (_sdl_surface != _sdl_realscreen && init) {
    /* When using a shadow surface, also set our palette on the real screen. This lets SDL
     * allocate as many colors (or approximations) as
     * possible, instead of using only the default SDL
     * palette. This allows us to get more colors exactly
     * right and might allow using better approximations for
     * other colors.
     *
     * Note that colors allocations are tried in-order, so
     * this favors colors further up into the palette. Also
     * note that if two colors from the same animation
     * sequence are approximated using the same color, that
     * animation will stop working.
     *
     * Since changing the system palette causes the colours
     * to change right away, and allocations might
     * drastically change, we can't use this for animation,
     * since that could cause weird coloring between the
     * palette change and the blitting below, so we only set
     * the real palette during initialisation.
     */
    SDL_SetColors(_sdl_realscreen, pal, _local_palette.first_dirty, _local_palette.count_dirty);
  }
 
  if (_sdl_surface != _sdl_realscreen && !init) {
    /* We're not using real hardware palette, but are letting SDL
     * approximate the palette during shadow -> screen copy. To
     * change the palette, we need to recopy the entire screen.
     *
     * Note that this operation can slow down the rendering
     * considerably, especially since changing the shadow
     * palette will need the next blit to re-detect the
     * best mapping of shadow palette colors to real palette
     * colors from scratch.
     */
    SDL_BlitSurface(_sdl_surface, nullptr, _sdl_realscreen, nullptr);
    SDL_UpdateRect(_sdl_realscreen, 0, 0, 0, 0);
  }
}
 
static void InitPalette()
{
  _local_palette = _cur_palette;
  _local_palette.first_dirty = 0;
  _local_palette.count_dirty = 256;
  UpdatePalette(true);
}
 
static void CheckPaletteAnim()
{
  if (_cur_palette.count_dirty != 0) {
    Blitter *blitter = BlitterFactory::GetCurrentBlitter();
 
    switch (blitter->UsePaletteAnimation()) {
      case Blitter::PALETTE_ANIMATION_VIDEO_BACKEND:
        UpdatePalette();
        break;
 
      case Blitter::PALETTE_ANIMATION_BLITTER:
        blitter->PaletteAnimate(_local_palette);
        break;
 
      case Blitter::PALETTE_ANIMATION_NONE:
        break;
 
      default:
        NOT_REACHED();
    }
    _cur_palette.count_dirty = 0;
  }
}
 
static void DrawSurfaceToScreen()
{
  PerformanceMeasurer framerate(PFE_VIDEO);
 
  int n = _num_dirty_rects;
  if (n == 0) return;
 
  _num_dirty_rects = 0;
 
  if (n > MAX_DIRTY_RECTS) {
    if (_sdl_surface != _sdl_realscreen) {
      SDL_BlitSurface(_sdl_surface, nullptr, _sdl_realscreen, nullptr);
    }
 
    SDL_UpdateRect(_sdl_realscreen, 0, 0, 0, 0);
  } else {
    if (_sdl_surface != _sdl_realscreen) {
      for (int i = 0; i < n; i++) {
        SDL_BlitSurface(_sdl_surface, &_dirty_rects[i], _sdl_realscreen, &_dirty_rects[i]);
      }
    }
 
    SDL_UpdateRects(_sdl_realscreen, n, _dirty_rects);
  }
}
 
static void DrawSurfaceToScreenThread()
{
  /* First tell the main thread we're started */
  std::unique_lock<std::recursive_mutex> lock(*_draw_mutex);
  _draw_signal->notify_one();
 
  /* Now wait for the first thing to draw! */
  _draw_signal->wait(*_draw_mutex);
 
  while (_draw_continue) {
    CheckPaletteAnim();
    /* Then just draw and wait till we stop */
    DrawSurfaceToScreen();
    _draw_signal->wait(lock);
  }
}
 
static const Dimension _default_resolutions[] = {
  { 640,  480},
  { 800,  600},
  {1024,  768},
  {1152,  864},
  {1280,  800},
  {1280,  960},
  {1280, 1024},
  {1400, 1050},
  {1600, 1200},
  {1680, 1050},
  {1920, 1200}
};
 
static void GetVideoModes()
{
  SDL_Rect **modes = SDL_ListModes(nullptr, SDL_SWSURFACE | SDL_FULLSCREEN);
  if (modes == nullptr) usererror("sdl: no modes available");
 
  _resolutions.clear();
 
  _all_modes = (SDL_ListModes(nullptr, SDL_SWSURFACE | (_fullscreen ? SDL_FULLSCREEN : 0)) == (void*)-1);
  if (modes == (void*)-1) {
    for (uint i = 0; i < lengthof(_default_resolutions); i++) {
      if (SDL_VideoModeOK(_default_resolutions[i].width, _default_resolutions[i].height, 8, SDL_FULLSCREEN) != 0) {
        _resolutions.push_back(_default_resolutions[i]);
      }
    }
  } else {
    for (int i = 0; modes[i]; i++) {
      uint w = modes[i]->w;
      uint h = modes[i]->h;
      if (w < 640 || h < 480) continue; // reject too small resolutions
      if (std::find(_resolutions.begin(), _resolutions.end(), Dimension(w, h)) != _resolutions.end()) continue;
      _resolutions.emplace_back(w, h);
    }
    if (_resolutions.empty()) usererror("No usable screen resolutions found!\n");
    SortResolutions();
  }
}
 
static void GetAvailableVideoMode(uint *w, uint *h)
{
  /* All modes available? */
  if (_all_modes || _resolutions.empty()) return;
 
  /* Is the wanted mode among the available modes? */
  if (std::find(_resolutions.begin(), _resolutions.end(), Dimension(*w, *h)) != _resolutions.end()) return;
 
  /* Use the closest possible resolution */
  uint best = 0;
  uint delta = Delta(_resolutions[0].width, *w) * Delta(_resolutions[0].height, *h);
  for (uint i = 1; i != _resolutions.size(); ++i) {
    uint newdelta = Delta(_resolutions[i].width, *w) * Delta(_resolutions[i].height, *h);
    if (newdelta < delta) {
      best = i;
      delta = newdelta;
    }
  }
  *w = _resolutions[best].width;
  *h = _resolutions[best].height;
}
 
bool VideoDriver_SDL::CreateMainSurface(uint w, uint h)
{
  SDL_Surface *newscreen, *icon;
  char caption[50];
  int bpp = BlitterFactory::GetCurrentBlitter()->GetScreenDepth();
  bool want_hwpalette;
 
  GetAvailableVideoMode(&w, &h);
 
  DEBUG(driver, 1, "SDL: using mode %ux%ux%d", w, h, bpp);
 
  if (bpp == 0) usererror("Can't use a blitter that blits 0 bpp for normal visuals");
 
  std::string icon_path = FioFindFullPath(BASESET_DIR, "openttd.32.bmp");
  if (!icon_path.empty()) {
    /* Give the application an icon */
    icon = SDL_LoadBMP(icon_path.c_str());
    if (icon != nullptr) {
      /* Get the colourkey, which will be magenta */
      uint32 rgbmap = SDL_MapRGB(icon->format, 255, 0, 255);
 
      SDL_SetColorKey(icon, SDL_SRCCOLORKEY, rgbmap);
      SDL_WM_SetIcon(icon, nullptr);
      SDL_FreeSurface(icon);
    }
  }
 
  if (_use_hwpalette == 2) {
    /* Default is to autodetect when to use SDL_HWPALETTE.
     * In this case, SDL_HWPALETTE is only used for 8bpp
     * blitters in fullscreen.
     *
     * When using an 8bpp blitter on a 8bpp system in
     * windowed mode with SDL_HWPALETTE, OpenTTD will claim
     * the system palette, making all other applications
     * get the wrong colours. In this case, we're better of
     * trying to approximate the colors we need using system
     * colors, using a shadow surface (see below).
     *
     * On a 32bpp system, SDL_HWPALETTE is ignored, so it
     * doesn't matter what we do.
     *
     * When using a 32bpp blitter on a 8bpp system, setting
     * SDL_HWPALETTE messes up rendering (at least on X11),
     * so we don't do that. In this case, SDL takes care of
     * color approximation using its own shadow surface
     * (which we can't force in 8bpp on 8bpp mode,
     * unfortunately).
     */
    want_hwpalette = bpp == 8 && _fullscreen && _support8bpp == S8BPP_HARDWARE;
  } else {
    /* User specified a value manually */
    want_hwpalette = _use_hwpalette;
  }
 
  if (want_hwpalette) DEBUG(driver, 1, "SDL: requesting hardware palette");
 
  /* Free any previously allocated shadow surface */
  if (_sdl_surface != nullptr && _sdl_surface != _sdl_realscreen) SDL_FreeSurface(_sdl_surface);
 
  if (_sdl_realscreen != nullptr) {
    if (_requested_hwpalette != want_hwpalette) {
      /* SDL (at least the X11 driver), reuses the
       * same window and palette settings when the bpp
       * (and a few flags) are the same. Since we need
       * to hwpalette value to change (in particular
       * when switching between fullscreen and
       * windowed), we restart the entire video
       * subsystem to force creating a new window.
       */
      DEBUG(driver, 0, "SDL: Restarting SDL video subsystem, to force hwpalette change");
      SDL_QuitSubSystem(SDL_INIT_VIDEO);
      SDL_InitSubSystem(SDL_INIT_VIDEO);
      ClaimMousePointer();
      SetupKeyboard();
    }
  }
  /* Remember if we wanted a hwpalette. We can't reliably query
   * SDL for the SDL_HWPALETTE flag, since it might get set even
   * though we didn't ask for it (when SDL creates a shadow
   * surface, for example). */
  _requested_hwpalette = want_hwpalette;
 
  /* DO NOT CHANGE TO HWSURFACE, IT DOES NOT WORK */
  newscreen = SDL_SetVideoMode(w, h, bpp, SDL_SWSURFACE | (want_hwpalette ? SDL_HWPALETTE : 0) | (_fullscreen ? SDL_FULLSCREEN : SDL_RESIZABLE));
  if (newscreen == nullptr) {
    DEBUG(driver, 0, "SDL: Couldn't allocate a window to draw on");
    return false;
  }
  _sdl_realscreen = newscreen;
 
  if (bpp == 8 && (_sdl_realscreen->flags & SDL_HWPALETTE) != SDL_HWPALETTE) {
    /* Using an 8bpp blitter, if we didn't get a hardware
     * palette (most likely because we didn't request one,
     * see above), we'll have to set up a shadow surface to
     * render on.
     *
     * Our palette will be applied to this shadow surface,
     * while the real screen surface will use the shared
     * system palette (which will partly contain our colors,
     * but most likely will not have enough free color cells
     * for all of our colors). SDL can use these two
     * palettes at blit time to approximate colors used in
     * the shadow surface using system colors automatically.
     *
     * Note that when using an 8bpp blitter on a 32bpp
     * system, SDL will create an internal shadow surface.
     * This shadow surface will have SDL_HWPALLETE set, so
     * we won't create a second shadow surface in this case.
     */
    DEBUG(driver, 1, "SDL: using shadow surface");
    newscreen = SDL_CreateRGBSurface(SDL_SWSURFACE, w, h, bpp, 0, 0, 0, 0);
    if (newscreen == nullptr) {
      DEBUG(driver, 0, "SDL: Couldn't allocate a shadow surface to draw on");
      return false;
    }
  }
 
  /* Delay drawing for this cycle; the next cycle will redraw the whole screen */
  _num_dirty_rects = 0;
 
  _screen.width = newscreen->w;
  _screen.height = newscreen->h;
  _screen.pitch = newscreen->pitch / (bpp / 8);
  _screen.dst_ptr = newscreen->pixels;
  _sdl_surface = newscreen;
 
  /* When in full screen, we will always have the mouse cursor
   * within the window, even though SDL does not give us the
   * appropriate event to know this. */
  if (_fullscreen) _cursor.in_window = true;
 
  Blitter *blitter = BlitterFactory::GetCurrentBlitter();
  blitter->PostResize();
 
  InitPalette();
 
  seprintf(caption, lastof(caption), "OpenTTD %s", _openttd_revision);
  SDL_WM_SetCaption(caption, caption);
 
  GameSizeChanged();
 
  return true;
}
 
bool VideoDriver_SDL::ClaimMousePointer()
{
  SDL_ShowCursor(0);
  return true;
}
 
struct VkMapping {
#if SDL_VERSION_ATLEAST(1, 3, 0)
  SDL_Keycode vk_from;
#else
  uint16 vk_from;
#endif
  byte vk_count;
  byte map_to;
};
 
#define AS(x, z) {x, 0, z}
#define AM(x, y, z, w) {x, (byte)(y - x), z}
 
static const VkMapping _vk_mapping[] = {
  /* Pageup stuff + up/down */
  AM(SDLK_PAGEUP, SDLK_PAGEDOWN, WKC_PAGEUP, WKC_PAGEDOWN),
  AS(SDLK_UP,     WKC_UP),
  AS(SDLK_DOWN,   WKC_DOWN),
  AS(SDLK_LEFT,   WKC_LEFT),
  AS(SDLK_RIGHT,  WKC_RIGHT),
 
  AS(SDLK_HOME,   WKC_HOME),
  AS(SDLK_END,    WKC_END),
 
  AS(SDLK_INSERT, WKC_INSERT),
  AS(SDLK_DELETE, WKC_DELETE),
 
  /* Map letters & digits */
  AM(SDLK_a, SDLK_z, 'A', 'Z'),
  AM(SDLK_0, SDLK_9, '0', '9'),
 
  AS(SDLK_ESCAPE,    WKC_ESC),
  AS(SDLK_PAUSE,     WKC_PAUSE),
  AS(SDLK_BACKSPACE, WKC_BACKSPACE),
 
  AS(SDLK_SPACE,     WKC_SPACE),
  AS(SDLK_RETURN,    WKC_RETURN),
  AS(SDLK_TAB,       WKC_TAB),
 
  /* Function keys */
  AM(SDLK_F1, SDLK_F12, WKC_F1, WKC_F12),
 
  /* Numeric part. */
  AM(SDLK_KP0, SDLK_KP9, '0', '9'),
  AS(SDLK_KP_DIVIDE,   WKC_NUM_DIV),
  AS(SDLK_KP_MULTIPLY, WKC_NUM_MUL),
  AS(SDLK_KP_MINUS,    WKC_NUM_MINUS),
  AS(SDLK_KP_PLUS,     WKC_NUM_PLUS),
  AS(SDLK_KP_ENTER,    WKC_NUM_ENTER),
  AS(SDLK_KP_PERIOD,   WKC_NUM_DECIMAL),
 
  /* Other non-letter keys */
  AS(SDLK_SLASH,        WKC_SLASH),
  AS(SDLK_SEMICOLON,    WKC_SEMICOLON),
  AS(SDLK_EQUALS,       WKC_EQUALS),
  AS(SDLK_LEFTBRACKET,  WKC_L_BRACKET),
  AS(SDLK_BACKSLASH,    WKC_BACKSLASH),
  AS(SDLK_RIGHTBRACKET, WKC_R_BRACKET),
 
  AS(SDLK_QUOTE,   WKC_SINGLEQUOTE),
  AS(SDLK_COMMA,   WKC_COMMA),
  AS(SDLK_MINUS,   WKC_MINUS),
  AS(SDLK_PERIOD,  WKC_PERIOD)
};
 
static uint ConvertSdlKeyIntoMy(SDL_keysym *sym, WChar *character)
{
  const VkMapping *map;
  uint key = 0;
 
  for (map = _vk_mapping; map != endof(_vk_mapping); ++map) {
    if ((uint)(sym->sym - map->vk_from) <= map->vk_count) {
      key = sym->sym - map->vk_from + map->map_to;
      break;
    }
  }
 
  /* check scancode for BACKQUOTE key, because we want the key left of "1", not anything else (on non-US keyboards) */
#if defined(_WIN32) || defined(__OS2__)
  if (sym->scancode == 41) key = WKC_BACKQUOTE;
#elif defined(__APPLE__)
  if (sym->scancode == 10) key = WKC_BACKQUOTE;
#elif defined(__SVR4) && defined(__sun)
  if (sym->scancode == 60) key = WKC_BACKQUOTE;
  if (sym->scancode == 49) key = WKC_BACKSPACE;
#elif defined(__sgi__)
  if (sym->scancode == 22) key = WKC_BACKQUOTE;
#else
  if (sym->scancode == 49) key = WKC_BACKQUOTE;
#endif
 
  /* META are the command keys on mac */
  if (sym->mod & KMOD_META)  key |= WKC_META;
  if (sym->mod & KMOD_SHIFT) key |= WKC_SHIFT;
  if (sym->mod & KMOD_CTRL)  key |= WKC_CTRL;
  if (sym->mod & KMOD_ALT)   key |= WKC_ALT;
 
  *character = sym->unicode;
  return key;
}
 
int VideoDriver_SDL::PollEvent()
{
  SDL_Event ev;
 
  if (!SDL_PollEvent(&ev)) return -2;
 
  switch (ev.type) {
    case SDL_MOUSEMOTION:
      if (_cursor.UpdateCursorPosition(ev.motion.x, ev.motion.y, true)) {
        SDL_WarpMouse(_cursor.pos.x, _cursor.pos.y);
      }
      HandleMouseEvents();
      break;
 
    case SDL_MOUSEBUTTONDOWN:
      if (_rightclick_emulate && SDL_GetModState() & KMOD_CTRL) {
        ev.button.button = SDL_BUTTON_RIGHT;
      }
 
      switch (ev.button.button) {
        case SDL_BUTTON_LEFT:
          _left_button_down = true;
          break;
 
        case SDL_BUTTON_RIGHT:
          _right_button_down = true;
          _right_button_clicked = true;
          break;
 
        case SDL_BUTTON_WHEELUP:   _cursor.wheel--; break;
        case SDL_BUTTON_WHEELDOWN: _cursor.wheel++; break;
 
        default: break;
      }
      HandleMouseEvents();
      break;
 
    case SDL_MOUSEBUTTONUP:
      if (_rightclick_emulate) {
        _right_button_down = false;
        _left_button_down = false;
        _left_button_clicked = false;
      } else if (ev.button.button == SDL_BUTTON_LEFT) {
        _left_button_down = false;
        _left_button_clicked = false;
      } else if (ev.button.button == SDL_BUTTON_RIGHT) {
        _right_button_down = false;
      }
      HandleMouseEvents();
      break;
 
    case SDL_ACTIVEEVENT:
      if (!(ev.active.state & SDL_APPMOUSEFOCUS)) break;
 
      if (ev.active.gain) { // mouse entered the window, enable cursor
        _cursor.in_window = true;
      } else {
        UndrawMouseCursor(); // mouse left the window, undraw cursor
        _cursor.in_window = false;
      }
      break;
 
    case SDL_QUIT:
      HandleExitGameRequest();
      break;
 
    case SDL_KEYDOWN: // Toggle full-screen on ALT + ENTER/F
      if ((ev.key.keysym.mod & (KMOD_ALT | KMOD_META)) &&
          (ev.key.keysym.sym == SDLK_RETURN || ev.key.keysym.sym == SDLK_f)) {
        ToggleFullScreen(!_fullscreen);
      } else {
        WChar character;
        uint keycode = ConvertSdlKeyIntoMy(&ev.key.keysym, &character);
        HandleKeypress(keycode, character);
      }
      break;
 
    case SDL_VIDEORESIZE: {
      int w = std::max(ev.resize.w, 64);
      int h = std::max(ev.resize.h, 64);
      CreateMainSurface(w, h);
      break;
    }
    case SDL_VIDEOEXPOSE: {
      /* Force a redraw of the entire screen. Note
       * that SDL 1.2 seems to do this automatically
       * in most cases, but 1.3 / 2.0 does not. */
            _num_dirty_rects = MAX_DIRTY_RECTS + 1;
      break;
    }
  }
  return -1;
}
 
const char *VideoDriver_SDL::Start(const StringList &parm)
{
  char buf[30];
  _use_hwpalette = GetDriverParamInt(parm, "hw_palette", 2);
 
  /* Just on the offchance the audio subsystem started before the video system,
   * check whether any part of SDL has been initialised before getting here.
   * Slightly duplicated with sound/sdl_s.cpp */
  int ret_code = 0;
  if (SDL_WasInit(SDL_INIT_EVERYTHING) == 0) {
    ret_code = SDL_Init(SDL_INIT_VIDEO | SDL_INIT_NOPARACHUTE);
  } else if (SDL_WasInit(SDL_INIT_VIDEO) == 0) {
    ret_code = SDL_InitSubSystem(SDL_INIT_VIDEO);
  }
  if (ret_code < 0) return SDL_GetError();
 
  this->UpdateAutoResolution();
 
  GetVideoModes();
  if (!CreateMainSurface(_cur_resolution.width, _cur_resolution.height)) {
    return SDL_GetError();
  }
 
  SDL_VideoDriverName(buf, sizeof buf);
  DEBUG(driver, 1, "SDL: using driver '%s'", buf);
 
  MarkWholeScreenDirty();
  SetupKeyboard();
 
  _draw_threaded = !GetDriverParamBool(parm, "no_threads") && !GetDriverParamBool(parm, "no_thread");
 
  return nullptr;
}
 
void VideoDriver_SDL::SetupKeyboard()
{
  SDL_EnableKeyRepeat(SDL_DEFAULT_REPEAT_DELAY, SDL_DEFAULT_REPEAT_INTERVAL);
  SDL_EnableUNICODE(1);
}
 
void VideoDriver_SDL::Stop()
{
  SDL_QuitSubSystem(SDL_INIT_VIDEO);
  if (SDL_WasInit(SDL_INIT_EVERYTHING) == 0) {
    SDL_Quit(); // If there's nothing left, quit SDL
  }
}
 
void VideoDriver_SDL::MainLoop()
{
  uint32 cur_ticks = SDL_GetTicks();
  uint32 last_cur_ticks = cur_ticks;
  uint32 next_tick = cur_ticks + MILLISECONDS_PER_TICK;
  uint32 mod;
  int numkeys;
  Uint8 *keys;
 
  CheckPaletteAnim();
 
  std::thread draw_thread;
  std::unique_lock<std::recursive_mutex> draw_lock;
  if (_draw_threaded) {
    /* Initialise the mutex first, because that's the thing we *need*
     * directly in the newly created thread. */
    _draw_mutex = new std::recursive_mutex();
    if (_draw_mutex == nullptr) {
      _draw_threaded = false;
    } else {
      draw_lock = std::unique_lock<std::recursive_mutex>(*_draw_mutex);
      _draw_signal = new std::condition_variable_any();
      _draw_continue = true;
 
      _draw_threaded = StartNewThread(&draw_thread, "ottd:draw-sdl", &DrawSurfaceToScreenThread);
 
      /* Free the mutex if we won't be able to use it. */
      if (!_draw_threaded) {
        draw_lock.unlock();
        draw_lock.release();
        delete _draw_mutex;
        delete _draw_signal;
        _draw_mutex = nullptr;
        _draw_signal = nullptr;
      } else {
        /* Wait till the draw mutex has started itself. */
        _draw_signal->wait(*_draw_mutex);
      }
    }
  }
 
  DEBUG(driver, 1, "SDL: using %sthreads", _draw_threaded ? "" : "no ");
 
  for (;;) {
    uint32 prev_cur_ticks = cur_ticks; // to check for wrapping
    InteractiveRandom(); // randomness
 
    while (PollEvent() == -1) {}
    if (_exit_game) break;
 
    mod = SDL_GetModState();
#if SDL_VERSION_ATLEAST(1, 3, 0)
    keys = SDL_GetKeyboardState(&numkeys);
#else
    keys = SDL_GetKeyState(&numkeys);
#endif
#if defined(_DEBUG)
    if (_shift_pressed)
#else
    /* Speedup when pressing tab, except when using ALT+TAB
     * to switch to another application */
#if SDL_VERSION_ATLEAST(1, 3, 0)
    if (keys[SDL_SCANCODE_TAB] && (mod & KMOD_ALT) == 0)
#else
    if (keys[SDLK_TAB] && (mod & KMOD_ALT) == 0)
#endif /* SDL_VERSION_ATLEAST(1, 3, 0) */
#endif /* defined(_DEBUG) */
    {
      if (!_networking && _game_mode != GM_MENU) _fast_forward |= 2;
    } else if (_fast_forward & 2) {
      _fast_forward = 0;
    }
 
    cur_ticks = SDL_GetTicks();
    if (cur_ticks >= next_tick || (_fast_forward && !_pause_mode) || cur_ticks < prev_cur_ticks) {
      _realtime_tick += cur_ticks - last_cur_ticks;
      last_cur_ticks = cur_ticks;
      next_tick = cur_ticks + MILLISECONDS_PER_TICK;
 
      bool old_ctrl_pressed = _ctrl_pressed;
 
      _ctrl_pressed  = !!(mod & KMOD_CTRL);
      _shift_pressed = !!(mod & KMOD_SHIFT);
 
      /* determine which directional keys are down */
      _dirkeys =
#if SDL_VERSION_ATLEAST(1, 3, 0)
        (keys[SDL_SCANCODE_LEFT]  ? 1 : 0) |
        (keys[SDL_SCANCODE_UP]    ? 2 : 0) |
        (keys[SDL_SCANCODE_RIGHT] ? 4 : 0) |
        (keys[SDL_SCANCODE_DOWN]  ? 8 : 0);
#else
        (keys[SDLK_LEFT]  ? 1 : 0) |
        (keys[SDLK_UP]    ? 2 : 0) |
        (keys[SDLK_RIGHT] ? 4 : 0) |
        (keys[SDLK_DOWN]  ? 8 : 0);
#endif
      if (old_ctrl_pressed != _ctrl_pressed) HandleCtrlChanged();
 
      /* The gameloop is the part that can run asynchronously. The rest
       * except sleeping can't. */
      if (_draw_mutex != nullptr) draw_lock.unlock();
 
      GameLoop();
 
      if (_draw_mutex != nullptr) draw_lock.lock();
 
      UpdateWindows();
      _local_palette = _cur_palette;
    } else {
      /* Release the thread while sleeping */
      if (_draw_mutex != nullptr) draw_lock.unlock();
      CSleep(1);
      if (_draw_mutex != nullptr) draw_lock.lock();
 
      NetworkDrawChatMessage();
      DrawMouseCursor();
    }
 
    /* End of the critical part. */
    if (_draw_mutex != nullptr && !HasModalProgress()) {
      _draw_signal->notify_one();
    } else {
      /* Oh, we didn't have threads, then just draw unthreaded */
      CheckPaletteAnim();
      DrawSurfaceToScreen();
    }
  }
 
  if (_draw_mutex != nullptr) {
    _draw_continue = false;
    /* Sending signal if there is no thread blocked
     * is very valid and results in noop */
    _draw_signal->notify_one();
    if (draw_lock.owns_lock()) draw_lock.unlock();
    draw_lock.release();
    draw_thread.join();
 
    delete _draw_mutex;
    delete _draw_signal;
 
    _draw_mutex = nullptr;
    _draw_signal = nullptr;
  }
}
 
bool VideoDriver_SDL::ChangeResolution(int w, int h)
{
  std::unique_lock<std::recursive_mutex> lock;
  if (_draw_mutex != nullptr) lock = std::unique_lock<std::recursive_mutex>(*_draw_mutex);
 
  return CreateMainSurface(w, h);
}
 
bool VideoDriver_SDL::ToggleFullscreen(bool fullscreen)
{
  std::unique_lock<std::recursive_mutex> lock;
  if (_draw_mutex != nullptr) lock = std::unique_lock<std::recursive_mutex>(*_draw_mutex);
 
  _fullscreen = fullscreen;
  GetVideoModes(); // get the list of available video modes
  bool ret = !_resolutions.empty() && CreateMainSurface(_cur_resolution.width, _cur_resolution.height);
 
  if (!ret) {
    /* switching resolution failed, put back full_screen to original status */
    _fullscreen ^= true;
  }
 
  return ret;
}
 
bool VideoDriver_SDL::AfterBlitterChange()
{
  return CreateMainSurface(_screen.width, _screen.height);
}
 
void VideoDriver_SDL::AcquireBlitterLock()
{
  if (_draw_mutex != nullptr) _draw_mutex->lock();
}
 
void VideoDriver_SDL::ReleaseBlitterLock()
{
  if (_draw_mutex != nullptr) _draw_mutex->unlock();
}
 
#endif /* WITH_SDL */