/* $Id$ */

/*
 * 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/>.
 */

/** @file sdl2_v.cpp Implementation of the SDL2 video driver. */

#ifdef WITH_SDL2

#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 "../window_func.h"
#include "../window_gui.h"
#include "sdl2_v.h"
#include <SDL.h>
#include <mutex>
#include <condition_variable>
#include <algorithm>
#if defined(__MINGW32__)
#include "../3rdparty/mingw-std-threads/mingw.mutex.h"
#include "../3rdparty/mingw-std-threads/mingw.condition_variable.h"
#endif

#include "../safeguards.h"

static FVideoDriver_SDL iFVideoDriver_SDL;

static SDL_Window *_sdl_window;
static SDL_Surface *_sdl_surface;
static SDL_Surface *_sdl_realscreen;

/** Whether the drawing is/may be done in a separate thread. */
static bool _draw_threaded;
/** Mutex to keep the access to the shared memory controlled. */
static std::recursive_mutex *_draw_mutex = nullptr;
/** Signal to draw the next frame. */
static std::condition_variable_any *_draw_signal = nullptr;
/** Should we keep continue drawing? */
static volatile bool _draw_continue;
static Palette _local_palette;
static SDL_Palette *_sdl_palette;

#define MAX_DIRTY_RECTS 100
static SDL_Rect _dirty_rects[MAX_DIRTY_RECTS];
static int _num_dirty_rects;

/* Size of window */
static int _window_size_w;
static int _window_size_h;

static std::string _editing_text;

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].a = 0;
	}

	SDL_SetPaletteColors(_sdl_palette, pal, _local_palette.first_dirty, _local_palette.count_dirty);
	SDL_SetSurfacePalette(_sdl_surface, _sdl_palette);

	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_SetSurfacePalette(_sdl_realscreen, _sdl_palette);
	}

	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_UpdateWindowSurface(_sdl_window);
	}
}

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_UpdateWindowSurface(_sdl_window);
	} 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_UpdateWindowSurfaceRects(_sdl_window, _dirty_rects, n);
	}
}

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 void GetVideoModes()
{
	int modes = SDL_GetNumDisplayModes(0);
	if (modes == 0) usererror("sdl: no modes available");

	_resolutions.clear();

	SDL_DisplayMode mode;
	for (int i = 0; i < modes; i++) {
		SDL_GetDisplayMode(0, i, &mode);

		uint w = mode.w;
		uint h = mode.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 (!_fullscreen || _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, bool resize)
{
	SDL_Surface *newscreen;
	char caption[50];
	int bpp = BlitterFactory::GetCurrentBlitter()->GetScreenDepth();

	GetAvailableVideoMode(&w, &h);

	DEBUG(driver, 1, "SDL2: using mode %ux%ux%d", w, h, bpp);

	if (bpp == 0) usererror("Can't use a blitter that blits 0 bpp for normal visuals");

	/* Free any previously allocated shadow surface */
	if (_sdl_surface != nullptr && _sdl_surface != _sdl_realscreen) SDL_FreeSurface(_sdl_surface);

	seprintf(caption, lastof(caption), "OpenTTD %s", _openttd_revision);

	if (_sdl_window == nullptr) {
		Uint32 flags = SDL_WINDOW_SHOWN;

		if (_fullscreen) {
			flags |= SDL_WINDOW_FULLSCREEN;
		} else {
			flags |= SDL_WINDOW_RESIZABLE;
		}

		_sdl_window = SDL_CreateWindow(
			caption,
			SDL_WINDOWPOS_UNDEFINED,
			SDL_WINDOWPOS_UNDEFINED,
			w, h,
			flags);

		if (_sdl_window == nullptr) {
			DEBUG(driver, 0, "SDL2: Couldn't allocate a window to draw on");
			return false;
		}

		char icon_path[MAX_PATH];
		if (FioFindFullPath(icon_path, lastof(icon_path), BASESET_DIR, "openttd.32.bmp") != nullptr) {
			/* Give the application an icon */
			SDL_Surface *icon = SDL_LoadBMP(icon_path);
			if (icon != nullptr) {
				/* Get the colourkey, which will be magenta */
				uint32 rgbmap = SDL_MapRGB(icon->format, 255, 0, 255);

				SDL_SetColorKey(icon, SDL_TRUE, rgbmap);
				SDL_SetWindowIcon(_sdl_window, icon);
				SDL_FreeSurface(icon);
			}
		}
	}

	if (resize) SDL_SetWindowSize(_sdl_window, w, h);

	newscreen = SDL_GetWindowSurface(_sdl_window);
	if (newscreen == NULL) {
		DEBUG(driver, 0, "SDL2: Couldn't get window surface: %s", SDL_GetError());
		return false;
	}

	_sdl_realscreen = newscreen;

	if (bpp == 8) {
		newscreen = SDL_CreateRGBSurfaceWithFormat(0, w, h, 8, SDL_PIXELFORMAT_INDEX8);

		if (newscreen == nullptr) {
			DEBUG(driver, 0, "SDL2: Couldn't allocate shadow surface: %s", SDL_GetError());
			return false;
		}
	}

	if (_sdl_palette == nullptr) {
		_sdl_palette = SDL_AllocPalette(256);
	}

	if (_sdl_palette == nullptr) {
		DEBUG(driver, 0, "SDL_AllocPalette() failed: %s", SDL_GetError());
		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();

	GameSizeChanged();

	return true;
}

bool VideoDriver_SDL::ClaimMousePointer()
{
	SDL_ShowCursor(0);
	return true;
}

static void SetTextInputRect()
{
	SDL_Rect winrect;
	Point pt = _focused_window->GetCaretPosition();
	winrect.x = _focused_window->left + pt.x;
	winrect.y = _focused_window->top  + pt.y;
	winrect.w = 1;
	winrect.h = FONT_HEIGHT_NORMAL;
	SDL_SetTextInputRect(&winrect);
}

void VideoDriver_SDL::EditBoxGainedFocus()
{
	if (!this->edit_box_focused) {
		SDL_StartTextInput();
		this->edit_box_focused = true;
	}
	SetTextInputRect();
}

void VideoDriver_SDL::EditBoxLostFocus()
{
	if (this->edit_box_focused) {
		SDL_StopTextInput();
		this->edit_box_focused = false;
	}
	/* Clear any marked string from the current edit box. */
	HandleTextInput(nullptr, true);
}

struct VkMapping {
	SDL_Keycode vk_from;
	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_KP_0, SDLK_KP_9, '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_GUI)   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;

	/* The mod keys have no character. Prevent '?' */
	if (sym->mod & KMOD_GUI ||
		sym->mod & KMOD_SHIFT ||
		sym->mod & KMOD_CTRL ||
		sym->mod & KMOD_ALT) {
		*character = WKC_NONE;
	} else {
		*character = sym->sym;
	}

	return key;
}

/**
 * Like ConvertSdlKeyIntoMy(), but takes an SDL_Keycode as input
 * instead of an SDL_Keysym.
 */
static uint ConvertSdlKeycodeIntoMy(SDL_Keycode kc)
{
	const VkMapping *map;
	uint key = 0;

	for (map = _vk_mapping; map != endof(_vk_mapping); ++map) {
		if ((uint)(kc - map->vk_from) <= map->vk_count) {
			key = kc - 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) */
	SDL_Scancode sc = SDL_GetScancodeFromKey(kc);
	if (sc == SDL_SCANCODE_GRAVE) key = WKC_BACKQUOTE;

	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_WarpMouseInWindow(_sdl_window, _cursor.pos.x, _cursor.pos.y);
			}
			HandleMouseEvents();
			break;

		case SDL_MOUSEWHEEL:
			if (ev.wheel.y > 0) {
				_cursor.wheel--;
			} else if (ev.wheel.y < 0) {
				_cursor.wheel++;
			}
			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;

				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_QUIT:
			HandleExitGameRequest();
			break;

		case SDL_KEYDOWN: // Toggle full-screen on ALT + ENTER/F
			if ((ev.key.keysym.mod & (KMOD_ALT | KMOD_GUI)) &&
					(ev.key.keysym.sym == SDLK_RETURN || ev.key.keysym.sym == SDLK_f)) {
				if (ev.key.repeat == 0) ToggleFullScreen(!_fullscreen);
			} else {
				WChar character;

				uint keycode = ConvertSdlKeyIntoMy(&ev.key.keysym, &character);
				// Only handle non-text keys here. Text is handled in
				// SDL_TEXTINPUT below.
				if (keycode == WKC_DELETE ||
					keycode == WKC_NUM_ENTER ||
					keycode == WKC_LEFT ||
					keycode == WKC_RIGHT ||
					keycode & WKC_META ||
					keycode & WKC_SHIFT ||
					keycode & WKC_CTRL ||
					keycode & WKC_ALT ||
					(keycode >= WKC_F1 && keycode <= WKC_F12) ||
					!IsValidChar(character, CS_ALPHANUMERAL)) {
					HandleKeypress(keycode, character);
				}
			}
			break;

		case SDL_TEXTINPUT: {
			if (EditBoxInGlobalFocus()) {
				HandleTextInput(nullptr, true);
				HandleTextInput(ev.text.text);
				SetTextInputRect();
				break;
			}
			WChar character;
			SDL_Keycode kc = SDL_GetKeyFromName(ev.text.text);
			uint keycode = ConvertSdlKeycodeIntoMy(kc);

			Utf8Decode(&character, ev.text.text);
			HandleKeypress(keycode, character);
			break;
		}

		case SDL_TEXTEDITING: {
			if (!EditBoxInGlobalFocus()) break;
			if (ev.edit.start == 0) {
				_editing_text = ev.edit.text;
			} else {
				_editing_text += ev.edit.text;
			}
			HandleTextInput(_editing_text.c_str(), true, _editing_text.c_str() + _editing_text.size());
			break;
		}

		case SDL_WINDOWEVENT: {
			if (ev.window.event == SDL_WINDOWEVENT_EXPOSED) {
				// Force a redraw of the entire screen.
				_num_dirty_rects = MAX_DIRTY_RECTS + 1;
			} else if (ev.window.event == SDL_WINDOWEVENT_SIZE_CHANGED) {
				int w = max(ev.window.data1, 64);
				int h = max(ev.window.data2, 64);
				CreateMainSurface(w, h, w != ev.window.data1 || h != ev.window.data2);
			} else if (ev.window.event == SDL_WINDOWEVENT_ENTER) {
				// mouse entered the window, enable cursor
				_cursor.in_window = true;
			} else if (ev.window.event == SDL_WINDOWEVENT_LEAVE) {
				// mouse left the window, undraw cursor
				UndrawMouseCursor();
				_cursor.in_window = false;
			}
			break;
		}
	}
	return -1;
}

const char *VideoDriver_SDL::Start(const char * const *parm)
{
	/* Explicitly disable hardware acceleration. Enabling this causes
	 * UpdateWindowSurface() to update the window's texture instead of
	 * its surface. */
	SDL_SetHint(SDL_HINT_FRAMEBUFFER_ACCELERATION , "0");

	/* 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_VIDEO) == 0) {
		ret_code = SDL_InitSubSystem(SDL_INIT_VIDEO);
	}
	if (ret_code < 0) return SDL_GetError();

	GetVideoModes();
	if (!CreateMainSurface(_cur_resolution.width, _cur_resolution.height, false)) {
		return SDL_GetError();
	}

	const char *dname = SDL_GetVideoDriver(0);
	DEBUG(driver, 1, "SDL2: using driver '%s'", dname);

	MarkWholeScreenDirty();

	_draw_threaded = GetDriverParam(parm, "no_threads") == nullptr && GetDriverParam(parm, "no_thread") == nullptr;

	return nullptr;
}

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;
	const 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, "SDL2: 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();
		keys = SDL_GetKeyboardState(&numkeys);

#if defined(_DEBUG)
		if (_shift_pressed)
#else
		/* Speedup when pressing tab, except when using ALT+TAB
		 * to switch to another application */
		if (keys[SDL_SCANCODE_TAB] && (mod & KMOD_ALT) == 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 (SDL_TICKS_PASSED(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;
			bool old_shift_pressed = _shift_pressed;

			_ctrl_pressed  = !!(mod & KMOD_CTRL) != _invert_ctrl;
			_shift_pressed = !!(mod & KMOD_SHIFT) != _invert_shift;

			/* determine which directional keys are down */
			_dirkeys =
				(keys[SDL_SCANCODE_LEFT]  ? 1 : 0) |
				(keys[SDL_SCANCODE_UP]    ? 2 : 0) |
				(keys[SDL_SCANCODE_RIGHT] ? 4 : 0) |
				(keys[SDL_SCANCODE_DOWN]  ? 8 : 0);
			if (old_ctrl_pressed != _ctrl_pressed) HandleCtrlChanged();
			if (old_shift_pressed != _shift_pressed) HandleShiftChanged();

			/* 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, true);
}

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);

	/* Remember current window size */
	if (fullscreen) {
		SDL_GetWindowSize(_sdl_window, &_window_size_w, &_window_size_h);

		/* Find fullscreen window size */
		SDL_DisplayMode dm;
		if (SDL_GetCurrentDisplayMode(0, &dm) < 0) {
			DEBUG(driver, 0, "SDL_GetCurrentDisplayMode() failed: %s", SDL_GetError());
		} else {
			SDL_SetWindowSize(_sdl_window, dm.w, dm.h);
		}
	}

	DEBUG(driver, 1, "SDL2: Setting %s", fullscreen ? "fullscreen" : "windowed");
	int ret = SDL_SetWindowFullscreen(_sdl_window, fullscreen ? SDL_WINDOW_FULLSCREEN : 0);
	if (ret == 0) {
		/* Switching resolution succeeded, set fullscreen value of window. */
		_fullscreen = fullscreen;
		if (!fullscreen) SDL_SetWindowSize(_sdl_window, _window_size_w, _window_size_h);
	} else {
		DEBUG(driver, 0, "SDL_SetWindowFullscreen() failed: %s", SDL_GetError());
	}

	return ret == 0;
}

bool VideoDriver_SDL::AfterBlitterChange()
{
	int w, h;
	SDL_GetWindowSize(_sdl_window, &w, &h);
	return CreateMainSurface(w, h, false);
}

void VideoDriver_SDL::AcquireBlitterLock()
{
	if (_draw_mutex != nullptr) _draw_mutex->lock();
}

void VideoDriver_SDL::ReleaseBlitterLock()
{
	if (_draw_mutex != nullptr) _draw_mutex->unlock();
}

#endif /* WITH_SDL2 */