Object properties: Add 'glow', disables light's effect if negative

The 'glow' value is added to the ambient light value.
Negative 'glow' disables light's effect on object colour, for faking
self-lighting, UI-style entities, or programmatic colouring in mods.

doc/lua_api.txt

@@ -4131,6 +4131,10 @@ Definition tables
     --  ^ Limit automatic rotation to this value in degrees per second,
     --    value < 0 no limit.
         backface_culling = true, -- false to disable backface_culling for model
+        glow = 0,
+    --  ^ Add this much extra lighting when calculating texture color.
+          value < 0 disables light's effect on texture color.
+          For faking self-lighting, UI style entities, or programmatic coloring in mods.
         nametag = "", -- by default empty, for players their name is shown if empty
         nametag_color = <color>, -- sets color of nametag as ColorSpec
         infotext = "", -- by default empty, text to be shown when pointed at object

src/content_cao.cpp

@@ -659,7 +659,10 @@ void GenericCAO::updateLight(u8 light_at_pos)
 
 void GenericCAO::updateLightNoCheck(u8 light_at_pos)
 {
-	u8 li = decode_light(light_at_pos);
+	if (m_glow < 0)
+		return;
+
+	u8 li = decode_light(light_at_pos + m_glow);
 	if (li != m_last_light)	{
 		m_last_light = li;
 		video::SColor color(255,li,li,li);
@@ -978,6 +981,7 @@ void GenericCAO::updateTextures(std::string mod)
 
 	m_previous_texture_modifier = m_current_texture_modifier;
 	m_current_texture_modifier = mod;
+	m_glow = m_prop.glow;
 
 	if (m_spritenode) {
 		if (m_prop.visual == "sprite") {

src/content_cao.h

@@ -106,6 +106,7 @@ private:
 	float m_step_distance_counter = 0.0f;
 	u8 m_last_light = 255;
 	bool m_is_visible = false;
+	s8 m_glow = 0;
 
 	std::vector<u16> m_children;
 

src/network/networkprotocol.h

@@ -179,6 +179,7 @@ with this program; if not, write to the Free Software Foundation, Inc.,
 	PROTOCOL VERSION 36:
 		Backwards compatibility drop
 		Add 'can_zoom' to player object properties
+		Add glow to object properties
 */
 
 #define LATEST_PROTOCOL_VERSION 36

src/object_properties.cpp

@@ -58,6 +58,7 @@ std::string ObjectProperties::dump()
 	os << ", makes_footstep_sound=" << makes_footstep_sound;
 	os << ", automatic_rotate="<< automatic_rotate;
 	os << ", backface_culling="<< backface_culling;
+	os << ", glow=" << glow;
 	os << ", nametag=" << nametag;
 	os << ", nametag_color=" << "\"" << nametag_color.getAlpha() << "," << nametag_color.getRed()
 			<< "," << nametag_color.getGreen() << "," << nametag_color.getBlue() << "\" ";
@@ -106,6 +107,7 @@ void ObjectProperties::serialize(std::ostream &os) const
 	os << serializeString(infotext);
 	os << serializeString(wield_item);
 	writeU8(os, can_zoom);
+	writeS8(os, glow);
 
 	// Add stuff only at the bottom.
 	// Never remove anything, because we don't want new versions of this
@@ -153,4 +155,5 @@ void ObjectProperties::deSerialize(std::istream &is)
 	infotext = deSerializeString(is);
 	wield_item = deSerializeString(is);
 	can_zoom = readU8(is);
+	glow = readS8(is);
 }

src/object_properties.h

@@ -50,6 +50,7 @@ struct ObjectProperties
 	bool automatic_face_movement_dir = false;
 	f32 automatic_face_movement_dir_offset = 0.0f;
 	bool backface_culling = true;
+	s8 glow = 0;
 	std::string nametag = "";
 	video::SColor nametag_color = video::SColor(255, 255, 255, 255);
 	f32 automatic_face_movement_max_rotation_per_sec = -1.0f;

src/script/common/c_content.cpp

@@ -277,6 +277,7 @@ void read_object_properties(lua_State *L, int index,
 	}
 	lua_pop(L, 1);
 	getboolfield(L, -1, "backface_culling", prop->backface_culling);
+	getintfield(L, -1, "glow", prop->glow);
 
 	getstringfield(L, -1, "nametag", prop->nametag);
 	lua_getfield(L, -1, "nametag_color");
@@ -362,6 +363,8 @@ void push_object_properties(lua_State *L, ObjectProperties *prop)
 	lua_setfield(L, -2, "automatic_face_movement_dir");
 	lua_pushboolean(L, prop->backface_culling);
 	lua_setfield(L, -2, "backface_culling");
+	lua_pushnumber(L, prop->glow);
+	lua_setfield(L, -2, "glow");
 	lua_pushlstring(L, prop->nametag.c_str(), prop->nametag.size());
 	lua_setfield(L, -2, "nametag");
 	push_ARGB8(L, prop->nametag_color);

src/script/common/c_converter.cpp

@@ -426,6 +426,19 @@ bool getintfield(lua_State *L, int table,
 	return got;
 }
 
+bool getintfield(lua_State *L, int table,
+		const char *fieldname, s8 &result)
+{
+	lua_getfield(L, table, fieldname);
+	bool got = false;
+	if (lua_isnumber(L, -1)) {
+		result = lua_tointeger(L, -1);
+		got = true;
+	}
+	lua_pop(L, 1);
+	return got;
+}
+
 bool getintfield(lua_State *L, int table,
 		const char *fieldname, u16 &result)
 {

src/script/common/c_converter.h

@@ -54,6 +54,8 @@ bool               getintfield(lua_State *L, int table,
                              const char *fieldname, int &result);
 bool               getintfield(lua_State *L, int table,
                              const char *fieldname, u8 &result);
+bool               getintfield(lua_State *L, int table,
+                             const char *fieldname, s8 &result);
 bool               getintfield(lua_State *L, int table,
                              const char *fieldname, u16 &result);
 bool               getintfield(lua_State *L, int table,