Option to make sky stars deterministic (#16529)

The star constellations are now based on a seed passed in StarParams.

doc/lua_api.md

@@ -9039,6 +9039,7 @@ child will follow movement and rotation of that bone.
             alpha channel is used to set overall star brightness.
             (default: `#ebebff69`)
         * `scale`: Float controlling the overall size of the stars (default: `1`)
+        * `star_seed`: Integer number which decides how to generate the sky stars. If set to zero, client picks a random number. (default: `0`)
 * `get_stars()`: returns a table with the current stars parameters as in
     `set_stars`.
 * `set_clouds(cloud_parameters)`: set cloud parameters

src/client/game.cpp

@@ -2488,7 +2488,7 @@ void Game::handleClientEvent_SetSky(ClientEvent *event, CameraOrientation *cam)
 		);
 	} else if (event->set_sky->type == "skybox" &&
 			event->set_sky->textures.size() == 6) {
-		// Disable the dyanmic mesh skybox:
+		// Disable the dynamic mesh skybox:
 		sky->setVisible(false);
 		// Set fog colors:
 		sky->setFallbackBgColor(event->set_sky->bgcolor);
@@ -2564,6 +2564,7 @@ void Game::handleClientEvent_SetStars(ClientEvent *event, CameraOrientation *cam
 	sky->setStarColor(event->star_params->starcolor);
 	sky->setStarScale(event->star_params->scale);
 	sky->setStarDayOpacity(event->star_params->day_opacity);
+	sky->setStarSeed(event->star_params->star_seed);
 	delete event->star_params;
 }
 

src/client/sky.cpp

@@ -807,6 +807,15 @@ void Sky::setStarCount(u16 star_count)
 	}
 }
 
+void Sky::setStarSeed(u64 star_seed)
+{
+	// Allow force updating star seed at game init.
+	if (m_star_params.star_seed != star_seed || m_first_update) {
+		m_star_params.star_seed = star_seed;
+		updateStars();
+	}
+}
+
 void Sky::updateStars()
 {
 	m_stars.reset(new scene::SMeshBuffer());
@@ -823,7 +832,8 @@ void Sky::updateStars()
 	vertices.reserve(4 * m_star_params.count);
 	indices.reserve(6 * m_star_params.count);
 
-	PcgRandom rgen(m_seed);
+	u64 star_seed = m_star_params.star_seed == 0 ? m_seed : m_star_params.star_seed;
+	PcgRandom rgen(star_seed);
 	float d = (0.006 / 2) * m_star_params.scale;
 	for (u16 i = 0; i < m_star_params.count; i++) {
 		v3f r = v3f(

src/client/sky.h

@@ -77,6 +77,7 @@ public:
 	void setStarColor(video::SColor star_color) { m_star_params.starcolor = star_color; }
 	void setStarScale(f32 star_scale) { m_star_params.scale = star_scale; updateStars(); }
 	void setStarDayOpacity(f32 day_opacity) { m_star_params.day_opacity = day_opacity; }
+	void setStarSeed(u64 star_seed);
 
 	bool getCloudsVisible() const { return m_clouds_visible && m_clouds_enabled; }
 	const video::SColorf &getCloudColor() const { return m_cloudcolor_f; }

src/network/clientpackethandler.cpp

@@ -1445,6 +1445,7 @@ void Client::handleCommand_HudSetStars(NetworkPacket *pkt)
 		>> stars.starcolor >> stars.scale;
 	try {
 		*pkt >> stars.day_opacity;
+		*pkt >> stars.star_seed;
 	} catch (PacketError &e) {};
 
 	ClientEvent *event = new ClientEvent();

src/script/lua_api/l_object.cpp

@@ -2452,6 +2452,7 @@ int ObjectRef::l_set_stars(lua_State *L)
 			"scale", star_params.scale);
 		star_params.day_opacity = getfloatfield_default(L, 2,
 			"day_opacity", star_params.day_opacity);
+		star_params.star_seed = getintfield_default(L, 2, "star_seed", star_params.star_seed);
 	}
 
 	getServer(L)->setStars(player, star_params);
@@ -2480,6 +2481,8 @@ int ObjectRef::l_get_stars(lua_State *L)
 	lua_setfield(L, -2, "scale");
 	lua_pushnumber(L, star_params.day_opacity);
 	lua_setfield(L, -2, "day_opacity");
+	lua_pushnumber(L, star_params.star_seed);
+	lua_setfield(L, -2, "star_seed");
 	return 1;
 }
 

src/server.cpp

@@ -1959,7 +1959,7 @@ void Server::SendSetStars(session_t peer_id, const StarParams &params)
 
 	pkt << params.visible << params.count
 		<< params.starcolor << params.scale
-		<< params.day_opacity;
+		<< params.day_opacity << params.star_seed;
 
 	Send(&pkt);
 }

src/skyparams.h

@@ -64,6 +64,7 @@ struct StarParams
 	video::SColor starcolor;
 	f32 scale;
 	f32 day_opacity;
+	u64 star_seed;
 };
 
 struct CloudParams
@@ -142,6 +143,7 @@ public:
 		stars.starcolor = video::SColor(105, 235, 235, 255);
 		stars.scale = 1;
 		stars.day_opacity = 0;
+		stars.star_seed = 0;
 		return stars;
 	}