Add: support for emscripten (play-OpenTTD-in-the-browser)

Emscripten compiles to WASM, which can be loaded via
HTML / JavaScript. This allows you to play OpenTTD inside a
browser.

Co-authored-by: milek7 <me@milek7.pl>

12 files changed, 155 insertions, 11 deletions

diff --git a/src/fontcache.cpp b/src/fontcache.cpp
index 051c4ee1d..79683d193 100644
--- a/src/fontcache.cpp
+++ b/src/fontcache.cpp
@@ -26,7 +26,6 @@
 #include "safeguards.h"
 
 static const int ASCII_LETTERSTART = 32; ///< First printable ASCII letter.
-static const int MAX_FONT_SIZE     = 72; ///< Maximum font size.
 
 /** Default heights for the different sizes of fonts. */
 static const int _default_font_height[FS_END]   = {10, 6, 18, 10};
@@ -202,6 +201,8 @@ bool SpriteFontCache::GetDrawGlyphShadow()
 
 FreeTypeSettings _freetype;
 
+static const int MAX_FONT_SIZE = 72; ///< Maximum font size.
+
 static const byte FACE_COLOUR = 1;
 static const byte SHADOW_COLOUR = 2;
 
diff --git a/src/gfx_type.h b/src/gfx_type.h
index 6fca2228d..452bc2c7e 100644
--- a/src/gfx_type.h
+++ b/src/gfx_type.h
@@ -162,7 +162,9 @@ struct DrawPixelInfo {
 union Colour {
 	uint32 data; ///< Conversion of the channel information to a 32 bit number.
 	struct {
-#if TTD_ENDIAN == TTD_BIG_ENDIAN
+#if defined(__EMSCRIPTEN__)
+		uint8 r, g, b, a;  ///< colour channels as used in browsers
+#elif TTD_ENDIAN == TTD_BIG_ENDIAN
 		uint8 a, r, g, b; ///< colour channels in BE order
 #else
 		uint8 b, g, r, a; ///< colour channels in LE order
@@ -177,7 +179,9 @@ union Colour {
 	 * @param a The channel for the alpha/transparency.
 	 */
 	Colour(uint8 r, uint8 g, uint8 b, uint8 a = 0xFF) :
-#if TTD_ENDIAN == TTD_BIG_ENDIAN
+#if defined(__EMSCRIPTEN__)
+		r(r), g(g), b(b), a(a)
+#elif TTD_ENDIAN == TTD_BIG_ENDIAN
 		a(a), r(r), g(g), b(b)
 #else
 		b(b), g(g), r(r), a(a)
diff --git a/src/ini.cpp b/src/ini.cpp
index 6948bc1ea..fc9b1e8fd 100644
--- a/src/ini.cpp
+++ b/src/ini.cpp
@@ -13,6 +13,9 @@
 #include "string_func.h"
 #include "fileio_func.h"
 #include <fstream>
+#ifdef __EMSCRIPTEN__
+#	include <emscripten.h>
+#endif
 
 #if (defined(_POSIX_C_SOURCE) && _POSIX_C_SOURCE >= 199309L) || (defined(_XOPEN_SOURCE) && _XOPEN_SOURCE >= 500)
 # include <unistd.h>
@@ -115,6 +118,10 @@ bool IniFile::SaveToDisk(const char *filename)
 	}
 #endif
 
+#ifdef __EMSCRIPTEN__
+	EM_ASM(if (window["openttd_syncfs"]) openttd_syncfs());
+#endif
+
 	return true;
 }
 
diff --git a/src/network/core/address.cpp b/src/network/core/address.cpp
index c2fecc7ff..1aaa0b5fb 100644
--- a/src/network/core/address.cpp
+++ b/src/network/core/address.cpp
@@ -299,7 +299,15 @@ static SOCKET ConnectLoopProc(addrinfo *runp)
 
 	if (!SetNoDelay(sock)) DEBUG(net, 1, "[%s] setting TCP_NODELAY failed", type);
 
-	if (connect(sock, runp->ai_addr, (int)runp->ai_addrlen) != 0) {
+	int err = connect(sock, runp->ai_addr, (int)runp->ai_addrlen);
+#ifdef __EMSCRIPTEN__
+	/* Emscripten is asynchronous, and as such a connect() is still in
+	 * progress by the time the call returns. */
+	if (err != 0 && errno != EINPROGRESS)
+#else
+	if (err != 0)
+#endif
+	{
 		DEBUG(net, 1, "[%s] could not connect %s socket: %s", type, family, strerror(errno));
 		closesocket(sock);
 		return INVALID_SOCKET;
diff --git a/src/network/core/os_abstraction.h b/src/network/core/os_abstraction.h
index 01ab68b27..be8b8f919 100644
--- a/src/network/core/os_abstraction.h
+++ b/src/network/core/os_abstraction.h
@@ -83,6 +83,16 @@ typedef unsigned long in_addr_t;
 #	include <errno.h>
 #	include <sys/time.h>
 #	include <netdb.h>
+
+#   if defined(__EMSCRIPTEN__)
+/* Emscripten doesn't support AI_ADDRCONFIG and errors out on it. */
+#		undef AI_ADDRCONFIG
+#		define AI_ADDRCONFIG 0
+/* Emscripten says it supports FD_SETSIZE fds, but it really only supports 64.
+ * https://github.com/emscripten-core/emscripten/issues/1711 */
+#		undef FD_SETSIZE
+#		define FD_SETSIZE 64
+#   endif
 #endif /* UNIX */
 
 /* OS/2 stuff */
@@ -148,12 +158,16 @@ typedef unsigned long in_addr_t;
  */
 static inline bool SetNonBlocking(SOCKET d)
 {
-#ifdef _WIN32
-	u_long nonblocking = 1;
+#ifdef __EMSCRIPTEN__
+	return true;
 #else
+#	ifdef _WIN32
+	u_long nonblocking = 1;
+#	else
 	int nonblocking = 1;
-#endif
+#	endif
 	return ioctlsocket(d, FIONBIO, &nonblocking) == 0;
+#endif
 }
 
 /**
@@ -163,10 +177,14 @@ static inline bool SetNonBlocking(SOCKET d)
  */
 static inline bool SetNoDelay(SOCKET d)
 {
+#ifdef __EMSCRIPTEN__
+	return true;
+#else
 	/* XXX should this be done at all? */
 	int b = 1;
 	/* The (const char*) cast is needed for windows */
 	return setsockopt(d, IPPROTO_TCP, TCP_NODELAY, (const char*)&b, sizeof(b)) == 0;
+#endif
 }
 
 /* Make sure these structures have the size we expect them to be */
diff --git a/src/network/network.cpp b/src/network/network.cpp
index 0e3d08630..a100b6b95 100644
--- a/src/network/network.cpp
+++ b/src/network/network.cpp
@@ -1154,3 +1154,14 @@ bool IsNetworkCompatibleVersion(const char *other)
 	const char *hash2 = ExtractNetworkRevisionHash(other);
 	return hash1 && hash2 && (strncmp(hash1, hash2, GITHASH_SUFFIX_LEN) == 0);
 }
+
+#ifdef __EMSCRIPTEN__
+extern "C" {
+
+void CDECL em_openttd_add_server(const char *host, int port)
+{
+	NetworkUDPQueryServer(NetworkAddress(host, port), true);
+}
+
+}
+#endif
diff --git a/src/network/network_content.cpp b/src/network/network_content.cpp
index 5e401d3e9..0140d3ef2 100644
--- a/src/network/network_content.cpp
+++ b/src/network/network_content.cpp
@@ -23,6 +23,10 @@
 #include <zlib.h>
 #endif
 
+#ifdef __EMSCRIPTEN__
+#	include <emscripten.h>
+#endif
+
 #include "../safeguards.h"
 
 extern bool HasScenario(const ContentInfo *ci, bool md5sum);
@@ -289,6 +293,13 @@ void ClientNetworkContentSocketHandler::DownloadSelectedContent(uint &files, uin
 {
 	bytes = 0;
 
+#ifdef __EMSCRIPTEN__
+	/* Emscripten is loaded via an HTTPS connection. As such, it is very
+	 * difficult to make HTTP connections. So always use the TCP method of
+	 * downloading content. */
+	fallback = true;
+#endif
+
 	ContentIDList content;
 	for (const ContentInfo *ci : this->infos) {
 		if (!ci->IsSelected() || ci->state == ContentInfo::ALREADY_HERE) continue;
@@ -535,6 +546,10 @@ void ClientNetworkContentSocketHandler::AfterDownload()
 			unlink(GetFullFilename(this->curInfo, false));
 		}
 
+#ifdef __EMSCRIPTEN__
+		EM_ASM(if (window["openttd_syncfs"]) openttd_syncfs());
+#endif
+
 		this->OnDownloadComplete(this->curInfo->id);
 	} else {
 		ShowErrorMessage(STR_CONTENT_ERROR_COULD_NOT_EXTRACT, INVALID_STRING_ID, WL_ERROR);
diff --git a/src/network/network_gui.cpp b/src/network/network_gui.cpp
index c430c47e5..47bf8fb69 100644
--- a/src/network/network_gui.cpp
+++ b/src/network/network_gui.cpp
@@ -39,6 +39,9 @@
 
 #include "../safeguards.h"
 
+#ifdef __EMSCRIPTEN__
+#	include <emscripten.h>
+#endif
 
 static void ShowNetworkStartServerWindow();
 static void ShowNetworkLobbyWindow(NetworkGameList *ngl);
@@ -475,6 +478,14 @@ public:
 		this->filter_editbox.cancel_button = QueryString::ACTION_CLEAR;
 		this->SetFocusedWidget(WID_NG_FILTER);
 
+		/* As the master-server doesn't support "websocket" servers yet, we
+		 * let "os/emscripten/pre.js" hardcode a list of servers people can
+		 * join. This means the serverlist is curated for now, but it is the
+		 * best we can offer. */
+#ifdef __EMSCRIPTEN__
+		EM_ASM(if (window["openttd_server_list"]) openttd_server_list());
+#endif
+
 		this->last_joined = NetworkGameListAddItem(NetworkAddress(_settings_client.network.last_host, _settings_client.network.last_port));
 		this->server = this->last_joined;
 		if (this->last_joined != nullptr) NetworkUDPQueryServer(this->last_joined->address);
@@ -615,6 +626,12 @@ public:
 		this->GetWidget<NWidgetStacked>(WID_NG_NEWGRF_SEL)->SetDisplayedPlane(sel == nullptr || !sel->online || sel->info.grfconfig == nullptr);
 		this->GetWidget<NWidgetStacked>(WID_NG_NEWGRF_MISSING_SEL)->SetDisplayedPlane(sel == nullptr || !sel->online || sel->info.grfconfig == nullptr || !sel->info.version_compatible || sel->info.compatible);
 
+#ifdef __EMSCRIPTEN__
+		this->SetWidgetDisabledState(WID_NG_FIND, true);
+		this->SetWidgetDisabledState(WID_NG_ADD, true);
+		this->SetWidgetDisabledState(WID_NG_START, true);
+#endif
+
 		this->DrawWidgets();
 	}
 
diff --git a/src/openttd.cpp b/src/openttd.cpp
index 4aeed3928..9cc5d2f20 100644
--- a/src/openttd.cpp
+++ b/src/openttd.cpp
@@ -73,6 +73,11 @@
 
 #include "safeguards.h"
 
+#ifdef __EMSCRIPTEN__
+#	include <emscripten.h>
+#	include <emscripten/html5.h>
+#endif
+
 void CallLandscapeTick();
 void IncreaseDate();
 void DoPaletteAnimations();
@@ -104,6 +109,15 @@ void CDECL usererror(const char *s, ...)
 	ShowOSErrorBox(buf, false);
 	if (VideoDriver::GetInstance() != nullptr) VideoDriver::GetInstance()->Stop();
 
+#ifdef __EMSCRIPTEN__
+	emscripten_exit_pointerlock();
+	/* In effect, the game ends here. As emscripten_set_main_loop() caused
+	 * the stack to be unwound, the code after MainLoop() in
+	 * openttd_main() is never executed. */
+	EM_ASM(if (window["openttd_syncfs"]) openttd_syncfs());
+	EM_ASM(if (window["openttd_abort"]) openttd_abort());
+#endif
+
 	exit(1);
 }
 
diff --git a/src/saveload/saveload.cpp b/src/saveload/saveload.cpp
index 999a381d7..5288f9047 100644
--- a/src/saveload/saveload.cpp
+++ b/src/saveload/saveload.cpp
@@ -45,6 +45,9 @@
 #include "../error.h"
 #include <atomic>
 #include <string>
+#ifdef __EMSCRIPTEN__
+#	include <emscripten.h>
+#endif
 
 #include "table/strings.h"
 
@@ -2495,6 +2498,10 @@ static void SaveFileDone()
 
 	InvalidateWindowData(WC_STATUS_BAR, 0, SBI_SAVELOAD_FINISH);
 	_sl.saveinprogress = false;
+
+#ifdef __EMSCRIPTEN__
+	EM_ASM(if (window["openttd_syncfs"]) openttd_syncfs());
+#endif
 }
 
 /** Set the error message from outside of the actual loading/saving of the game (AfterLoadGame and friends) */
diff --git a/src/video/sdl2_v.cpp b/src/video/sdl2_v.cpp
index 09d0e8a0b..68b0aa983 100644
--- a/src/video/sdl2_v.cpp
+++ b/src/video/sdl2_v.cpp
@@ -27,6 +27,10 @@
 #include <mutex>
 #include <condition_variable>
 #include <algorithm>
+#ifdef __EMSCRIPTEN__
+#	include <emscripten.h>
+#	include <emscripten/html5.h>
+#endif
 
 #include "../safeguards.h"
 
@@ -673,7 +677,19 @@ void VideoDriver_SDL::LoopOnce()
 	InteractiveRandom(); // randomness
 
 	while (PollEvent() == -1) {}
-	if (_exit_game) return;
+	if (_exit_game) {
+#ifdef __EMSCRIPTEN__
+		/* Emscripten is event-driven, and as such the main loop is inside
+		 * the browser. So if _exit_game goes true, the main loop ends (the
+		 * cancel call), but we still have to call the cleanup that is
+		 * normally done at the end of the main loop for non-Emscripten.
+		 * After that, Emscripten just halts, and the HTML shows a nice
+		 * "bye, see you next time" message. */
+		emscripten_cancel_main_loop();
+		MainLoopCleanup();
+#endif
+		return;
+	}
 
 	mod = SDL_GetModState();
 	keys = SDL_GetKeyboardState(&numkeys);
@@ -722,9 +738,17 @@ void VideoDriver_SDL::LoopOnce()
 		_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();
+		if (_draw_mutex != nullptr) {
+			draw_lock.unlock();
+			CSleep(1);
+			draw_lock.lock();
+		} else {
+/* Emscripten is running an event-based mainloop; there is already some
+ * downtime between each iteration, so no need to sleep. */
+#ifndef __EMSCRIPTEN__
+			CSleep(1);
+#endif
+		}
 
 		NetworkDrawChatMessage();
 		DrawMouseCursor();
@@ -778,6 +802,10 @@ void VideoDriver_SDL::MainLoop()
 
 	DEBUG(driver, 1, "SDL2: using %sthreads", _draw_threaded ? "" : "no ");
 
+#ifdef __EMSCRIPTEN__
+	/* Run the main loop event-driven, based on RequestAnimationFrame. */
+	emscripten_set_main_loop_arg(&this->EmscriptenLoop, this, 0, 1);
+#else
 	while (!_exit_game) {
 		LoopOnce();
 	}
@@ -803,6 +831,15 @@ void VideoDriver_SDL::MainLoopCleanup()
 		_draw_mutex = nullptr;
 		_draw_signal = nullptr;
 	}
+
+#ifdef __EMSCRIPTEN__
+	emscripten_exit_pointerlock();
+	/* In effect, the game ends here. As emscripten_set_main_loop() caused
+	 * the stack to be unwound, the code after MainLoop() in
+	 * openttd_main() is never executed. */
+	EM_ASM(if (window["openttd_syncfs"]) openttd_syncfs());
+	EM_ASM(if (window["openttd_exit"]) openttd_exit());
+#endif
 }
 
 bool VideoDriver_SDL::ChangeResolution(int w, int h)
diff --git a/src/video/sdl2_v.h b/src/video/sdl2_v.h
index 6318c403f..c2ac87a06 100644
--- a/src/video/sdl2_v.h
+++ b/src/video/sdl2_v.h
@@ -46,6 +46,11 @@ private:
 	void MainLoopCleanup();
 	bool CreateMainSurface(uint w, uint h, bool resize);
 
+#ifdef __EMSCRIPTEN__
+	/* Convert a constant pointer back to a non-constant pointer to a member function. */
+	static void EmscriptenLoop(void *self) { ((VideoDriver_SDL *)self)->LoopOnce(); }
+#endif
+
 	/**
 	 * This is true to indicate that keyboard input is in text input mode, and SDL_TEXTINPUT events are enabled.
 	 */