Calling a script function

From CryWiki

Jump to: navigation, search


About
Author ins
Skill Level Beginner
Compatibility 1.2+
Requirements Compiler
Date Added 15/09/2008
Last Modified 15/09/2008

Calling a script function

This document explains how to call a script function from c++. A script function is a function written in lua. We will call a function in Singleplayer.lua for this example. (Located at Scripts/GameRules/SinglePlayer.lua)


There are 2 ways to call a lua function

  1. Using BeginCall, PushParam and EndCall
  2. Using static functions of the Script struct

For most cases, the second method will work just fine, and it takes fewer lines to write. If you need to pass a lot of arguments to the lua function, you'll have to use the first method.

Using BeginCall, PushParam and EndCall

  1. Call BeginCall
  2. Push all parameters with PushParam
  3. Call EndCall


C++
// Get the scriptsystem
IScriptSystem *pScriptSystem = gEnv->pScriptSystem;
 
// Get the ScriptTable object of the current gamerules.
IScriptTable *pScriptTable = g_pGame->GetGameRules()->GetEntity()->GetScriptTable();
 
// Get the object to pass on to the function, here the client actor.
IScriptTable *pClientActor = g_pGame->GetIGameFramework()->GetClientActor()->GetEntity()->GetScriptTable();
 
// This will store the return value
float returnValue;
 
// Make sure we don't have NULL pointers
if (pScriptSystem && pScriptTable && pClientActor)
{
	// Call the GetEnergyAbsorption function on the pScriptTable object (which is the script table of the gamerules)
	pScriptSystem->BeginCall(pScriptTable, "GetEnergyAbsorption");
 
	// ALWAYS pass on the ScriptTable as first parameter, even when calling a function without arguments
	pScriptSystem->PushFuncParam(pScriptTable);
 
	// Push our actual parameter
	pScriptSystem->PushFuncParam(pClientActor);
 
	// End the call, and store the result in returnValue
	pScriptSystem->EndCall(returnValue);
 
	CryLogAlways("The function returned %f", returnValue);
 
 
} else { // (pScriptTable or pScriptSystem or pClientActor) == NULL 
	CryLogAlways("Failed execute the function.");
}


Note
When calling a function without arguments, you still have to pass on the ScriptTable of the entity as an argument.

Using static functions of the Script struct

These functions can be found at Code/CryEngine/CryCommon/ScriptHelpers.h, inside the Script struct. All the functions are static so you don't need to create an instance of the Script struct.


C++
// Get the ScriptTable object of the current gamerules.
IScriptTable *pScriptTable = g_pGame->GetGameRules()->GetEntity()->GetScriptTable();
 
// This will store the return value
float returnValue;
 
// Check if the function exists
HSCRIPTFUNCTION	getEnergyAbsorption = 0;
if (pScriptTable && pScriptTable->GetValue("GetEnergyAbsorption", getEnergyAbsorption))
{
	// Always pass on pScriptTable as the first argument, even when calling a function without arguments
	Script::CallReturn(gEnv->pScriptSystem, getEnergyAbsorption, pScriptTable, returnValue);
 
	CryLogAlways("The function returned %f", returnValue);
} else { // function does not exist
	CryLogAlways("The function does not exist.");
}


Aside from CallReturn, there's also:

  • Script::Call - For a function that doesn't return a value, or you don't need it.
  • Script::CallMethod - Automaticly passes on the ScriptTable, you can also use a string for the function here


C++
IScriptTable *pScriptTable = g_pGame->GetGameRules()->GetEntity()->GetScriptTable();
Script::CallMethod(pScriptTable, "EndLevel");


Retrieved from "http://wiki.crymod.com/index.php/Calling_a_script_function"
Personal tools