From 93eb0794d6f7366df5fb375855b2e5e5888304c6 Mon Sep 17 00:00:00 2001
From: you <ovvv@web.de>
Date: Sat, 31 Mar 2018 14:48:38 +0200
Subject: [PATCH] ObjectRef: Add add_velocity() (#3208)

Allow changing the velocity of objects relatively to their current velocity
---
 builtin/game/falling.lua        |  2 +-
 doc/lua_api.txt                 |  4 ++++
 src/content_sao.h               |  4 ++++
 src/script/lua_api/l_object.cpp | 15 +++++++++++++++
 src/script/lua_api/l_object.h   |  3 +++
 5 files changed, 27 insertions(+), 1 deletion(-)

diff --git a/builtin/game/falling.lua b/builtin/game/falling.lua
index 974ba395..4ebe39f5 100644
--- a/builtin/game/falling.lua
+++ b/builtin/game/falling.lua
@@ -39,7 +39,7 @@ core.register_entity(":__builtin:falling_node", {
 
 	on_activate = function(self, staticdata)
 		self.object:set_armor_groups({immortal = 1})
-		
+
 		local ds = core.deserialize(staticdata)
 		if ds and ds.node then
 			self:set_node(ds.node, ds.meta)
diff --git a/doc/lua_api.txt b/doc/lua_api.txt
index 69c4b326..00f5e3f7 100644
--- a/doc/lua_api.txt
+++ b/doc/lua_api.txt
@@ -4029,6 +4029,10 @@ This is basically a reference to a C++ `ServerActiveObject`
 ##### LuaEntitySAO-only (no-op for other objects)
 * `set_velocity(vel)`
     * `vel` is a vector, e.g. `{x=0.0, y=2.3, z=1.0}`
+* `add_velocity(vel)`
+    * `vel` is a vector, e.g. `{x=0.0, y=2.3, z=1.0}`
+    * In comparison to using get_velocity, adding the velocity and then using
+      set_velocity, add_velocity is supposed to avoid synchronization problems.
 * `get_velocity()`: returns the velocity, a vector
 * `set_acceleration(acc)`
     * `acc` is a vector
diff --git a/src/content_sao.h b/src/content_sao.h
index 509f477d..3f75a789 100644
--- a/src/content_sao.h
+++ b/src/content_sao.h
@@ -121,6 +121,10 @@ public:
 	s16 getHP() const;
 	/* LuaEntitySAO-specific */
 	void setVelocity(v3f velocity);
+	void addVelocity(v3f velocity)
+	{
+		m_velocity += velocity;
+	}
 	v3f getVelocity();
 	void setAcceleration(v3f acceleration);
 	v3f getAcceleration();
diff --git a/src/script/lua_api/l_object.cpp b/src/script/lua_api/l_object.cpp
index e4c478df..b3c3bdf6 100644
--- a/src/script/lua_api/l_object.cpp
+++ b/src/script/lua_api/l_object.cpp
@@ -850,6 +850,20 @@ int ObjectRef::l_set_velocity(lua_State *L)
 	return 0;
 }
 
+// add_velocity(self, {x=num, y=num, z=num})
+int ObjectRef::l_add_velocity(lua_State *L)
+{
+	NO_MAP_LOCK_REQUIRED;
+	ObjectRef *ref = checkobject(L, 1);
+	LuaEntitySAO *co = getluaobject(ref);
+	if (!co)
+		return 0;
+	v3f pos = checkFloatPos(L, 2);
+	// Do it
+	co->addVelocity(pos);
+	return 0;
+}
+
 // get_velocity(self)
 int ObjectRef::l_get_velocity(lua_State *L)
 {
@@ -1840,6 +1854,7 @@ const luaL_Reg ObjectRef::methods[] = {
 	luamethod(ObjectRef, get_nametag_attributes),
 	// LuaEntitySAO-only
 	luamethod_aliased(ObjectRef, set_velocity, setvelocity),
+	luamethod(ObjectRef, add_velocity),
 	luamethod_aliased(ObjectRef, get_velocity, getvelocity),
 	luamethod_aliased(ObjectRef, set_acceleration, setacceleration),
 	luamethod_aliased(ObjectRef, get_acceleration, getacceleration),
diff --git a/src/script/lua_api/l_object.h b/src/script/lua_api/l_object.h
index 58cfe714..21c215c3 100644
--- a/src/script/lua_api/l_object.h
+++ b/src/script/lua_api/l_object.h
@@ -161,6 +161,9 @@ private:
 	// set_velocity(self, {x=num, y=num, z=num})
 	static int l_set_velocity(lua_State *L);
 
+	// add_velocity(self, {x=num, y=num, z=num})
+	static int l_add_velocity(lua_State *L);
+
 	// get_velocity(self)
 	static int l_get_velocity(lua_State *L);