Add AllowUnitTransport callin

cont/base/springcontent/LuaGadgets/callins.lua

@@ -99,6 +99,7 @@ CALLIN_LIST = {
 	"AllowUnitCreation",
 	"AllowUnitTransfer",
 	"AllowUnitBuildStep",
+	"AllowUnitTransport",
 	"AllowFeatureBuildStep",
 	"AllowFeatureCreation",
 	"AllowResourceLevel",

cont/base/springcontent/LuaGadgets/gadgets.lua

@@ -1137,6 +1137,18 @@ function gadgetHandler:AllowUnitBuildStep(builderID, builderTeam,
 end
 
 
+function gadgetHandler:AllowUnitTransport(transporterID, transporterUnitDefID, transporterTeam,
+                                          transporteeID, transporteeUnitDefID, transporteeTeam)
+  for _,g in r_ipairs(self.AllowUnitTransportList) do
+    if (not g:AllowUnitTransport(transporterID, transporterUnitDefID, transporterTeam,
+                                 transporteeID, transporteeUnitDefID, transporteeTeam)) then
+      return false
+    end
+  end
+  return true
+end
+
+
 function gadgetHandler:AllowFeatureBuildStep(builderID, builderTeam,
                                              featureID, featureDefID, part)
   for _,g in r_ipairs(self.AllowFeatureBuildStepList) do

doc/changelog.txt

@@ -61,6 +61,9 @@ Lua:
    them available in `Spring.MoveCtrl.SetMoveDef` but beware the perf cost.
  - new TextEditing(utf8, start, length) callin, which holds the IME editing composition (https://wiki.libsdl.org/Tutorials/TextInput)
  - new SDLSetTextInputRect(x, y, w, h), SDLStartTextInput() and SDLStopTextInput() functions for controlling IME input from Lua
+ - Add AllowUnitTransport callin. Called when the engine tests whether unit A can transport unit B. Returning true will let
+   the engine decide, returning false will force the engine to disallow transportation (for this specific call).
+
 
 AI:
  - reveal unit's captureProgress, buildProgress and paralyzeDamage params through

rts/Lua/LuaHandleSynced.cpp

@@ -588,6 +588,34 @@ bool CSyncedLuaHandle::AllowUnitBuildStep(const CUnit* builder,
 }
 
 
+bool CSyncedLuaHandle::AllowUnitTransport(const CUnit* transporter,
+                                          const CUnit* transportee)
+{
+	LUA_CALL_IN_CHECK(L, true);
+	luaL_checkstack(L, 8, __func__);
+
+	static const LuaHashString cmdStr(__func__);
+	if (!cmdStr.GetGlobalFunc(L))
+		return true; // the call is not defined
+
+	lua_pushnumber(L, transporter->id);
+	lua_pushnumber(L, transporter->unitDef->id);
+	lua_pushnumber(L, transporter->team);
+	lua_pushnumber(L, transportee->id);
+	lua_pushnumber(L, transportee->unitDef->id);
+	lua_pushnumber(L, transportee->team);
+
+	// call the function
+	if (!RunCallIn(L, cmdStr, 6, 1))
+		return true;
+
+	// get the results
+	const bool retval = luaL_optboolean(L, -1, true);
+	lua_pop(L, 1);
+	return retval;
+}
+
+
 bool CSyncedLuaHandle::AllowFeatureCreation(const FeatureDef* featureDef,
                                      int teamID, const float3& pos)
 {

rts/Lua/LuaHandleSynced.h

@@ -58,6 +58,7 @@ class CSyncedLuaHandle : public CLuaHandle
 		bool AllowUnitCreation(const UnitDef* unitDef, const CUnit* builder, const BuildInfo* buildInfo);
 		bool AllowUnitTransfer(const CUnit* unit, int newTeam, bool capture);
 		bool AllowUnitBuildStep(const CUnit* builder, const CUnit* unit, float part);
+		bool AllowUnitTransport(const CUnit* transporter, const CUnit* transportee);
 		bool AllowFeatureCreation(const FeatureDef* featureDef, int allyTeamID, const float3& pos);
 		bool AllowFeatureBuildStep(const CUnit* builder, const CFeature* feature, float part);
 		bool AllowResourceLevel(int teamID, const string& type, float level);

rts/Sim/Units/Unit.cpp

@@ -2489,6 +2489,10 @@ bool CUnit::CanTransport(const CUnit* unit) const
 		return false;
 	if (unit->GetTransporter() != NULL)
 		return false;
+
+	if (!eventHandler.AllowUnitTransport(this, unit))
+		return false;
+
 	if (!unit->unitDef->transportByEnemy && !teamHandler->AlliedTeams(unit->team, team))
 		return false;
 	if (transportCapacityUsed >= unitDef->transportCapacity)

rts/System/EventClient.cpp

@@ -50,6 +50,7 @@ bool CEventClient::AllowCommand(const CUnit* unit, const Command& cmd, bool from
 bool CEventClient::AllowUnitCreation(const UnitDef* unitDef, const CUnit* builder, const BuildInfo* buildInfo) { return true; }
 bool CEventClient::AllowUnitTransfer(const CUnit* unit, int newTeam, bool capture) { return true; }
 bool CEventClient::AllowUnitBuildStep(const CUnit* builder, const CUnit* unit, float part) { return true; }
+bool CEventClient::AllowUnitTransport(const CUnit* transporter, const CUnit* transportee) { return true; }
 bool CEventClient::AllowFeatureCreation(const FeatureDef* featureDef, int allyTeamID, const float3& pos) { return true; }
 bool CEventClient::AllowFeatureBuildStep(const CUnit* builder, const CFeature* feature, float part) { return true; }
 bool CEventClient::AllowResourceLevel(int teamID, const string& type, float level) { return true; }

rts/System/EventClient.h

@@ -198,6 +198,7 @@ class CEventClient
 		virtual bool AllowUnitCreation(const UnitDef* unitDef, const CUnit* builder, const BuildInfo* buildInfo);
 		virtual bool AllowUnitTransfer(const CUnit* unit, int newTeam, bool capture);
 		virtual bool AllowUnitBuildStep(const CUnit* builder, const CUnit* unit, float part);
+		virtual bool AllowUnitTransport(const CUnit* transporter, const CUnit* transportee);
 		virtual bool AllowFeatureCreation(const FeatureDef* featureDef, int allyTeamID, const float3& pos);
 		virtual bool AllowFeatureBuildStep(const CUnit* builder, const CFeature* feature, float part);
 		virtual bool AllowResourceLevel(int teamID, const string& type, float level);

rts/System/EventHandler.cpp

@@ -266,6 +266,12 @@ bool CEventHandler::AllowUnitBuildStep(const CUnit* builder, const CUnit* unit,
 }
 
 
+bool CEventHandler::AllowUnitTransport(const CUnit* transporter, const CUnit* transportee)
+{
+	return ControlIterateDefTrue(listAllowUnitTransport, &CEventClient::AllowUnitTransport, transporter, transportee);
+}
+
+
 bool CEventHandler::AllowFeatureCreation(const FeatureDef* featureDef, int allyTeamID, const float3& pos)
 {
 	return ControlIterateDefTrue(listAllowFeatureCreation, &CEventClient::AllowFeatureCreation, featureDef, allyTeamID, pos);

rts/System/EventHandler.h

@@ -139,6 +139,7 @@ class CEventHandler
 		bool AllowUnitCreation(const UnitDef* unitDef, const CUnit* builder, const BuildInfo* buildInfo);
 		bool AllowUnitTransfer(const CUnit* unit, int newTeam, bool capture);
 		bool AllowUnitBuildStep(const CUnit* builder, const CUnit* unit, float part);
+		bool AllowUnitTransport(const CUnit* transporter, const CUnit* transportee);
 		bool AllowFeatureCreation(const FeatureDef* featureDef, int allyTeamID, const float3& pos);
 		bool AllowFeatureBuildStep(const CUnit* builder, const CFeature* feature, float part);
 		bool AllowResourceLevel(int teamID, const string& type, float level);

rts/System/Events.def

@@ -164,6 +164,7 @@
 	SETUP_EVENT(AllowUnitCreation,      MANAGED_BIT | CONTROL_BIT)
 	SETUP_EVENT(AllowUnitTransfer,      MANAGED_BIT | CONTROL_BIT)
 	SETUP_EVENT(AllowUnitBuildStep,     MANAGED_BIT | CONTROL_BIT)
+	SETUP_EVENT(AllowUnitTransport,     MANAGED_BIT | CONTROL_BIT)
 	SETUP_EVENT(AllowFeatureCreation,   MANAGED_BIT | CONTROL_BIT)
 	SETUP_EVENT(AllowFeatureBuildStep,  MANAGED_BIT | CONTROL_BIT)
 	SETUP_EVENT(AllowResourceLevel,     MANAGED_BIT | CONTROL_BIT)