Trigger Map Scripts By Flag

Triggering Map Scripts With Flags

In vanilla emerald, mapscripts are conditionally triggered based on the value of a provided variable. This small change allows mapscripts to be triggered based on the value of a flag instead. This is useful if you have an event/cutscene that you need to activate only once. This also works just fine with poryscript.

To add this feature, you will modify the function MapHeaderCheckScriptTable in the file src\script.c. Simply replace that entire function with the following:

u8 *MapHeaderCheckScriptTable(u8 tag)
{
    u8 *ptr = MapHeaderGetScriptTable(tag);

    if (!ptr)
        return NULL;

    while (1)
    {
        u16 varIndex1;
        u16 varIndex2;
        bool8 isFlag;
        bool8 flagSet;

        // Read first var (or .2byte terminal value)
        varIndex1 = T1_READ_16(ptr);
        if (!varIndex1)
            return NULL; // Reached end of table
        ptr += 2;

        // Read second var
        varIndex2 = T1_READ_16(ptr);
        ptr += 2;

        isFlag = varIndex1 < VARS_START;
        flagSet = isFlag && FlagGet(varIndex1);

        // Run map script if vars are equal
        if (isFlag
         && ((VarGet(varIndex2) != 0 && flagSet)
          || (VarGet(varIndex2) == 0 && !flagSet))) {
            return T2_READ_PTR(ptr);
        }
        else if (VarGet(varIndex1) == VarGet(varIndex2)) {
            return T2_READ_PTR(ptr);
        }
        ptr += 4;
    }
}

To make use of this, write any mapscript as you normally would but substituting a flag in place of the var. If the value provided is zero, the mapscript will trigger when the flag is not set. If the value is not zero, the mapscript will trigger if the flag is set.

For example, the following will trigger a script when the flag FLAG_DO_A_THING is set.

MyMap_MapScripts::
	map_script MAP_SCRIPT_ON_FRAME_TABLE, NeoBay_MapScripts_MAP_SCRIPT_ON_FRAME_TABLE
	.byte 0

MyMap_MapScripts_MAP_SCRIPT_ON_FRAME_TABLE:
	map_script_2 FLAG_DO_A_THING, 1, MyMap_EventScript_DoSomething
	.2byte 0

It's that easy!

Caveats

Due to the values associated with them, this will NOT work for "Special" flags, i.e. those beginning at SPECIAL_FLAGS_START. Those overlap with the VAR indices, and thus will be read as though they are VARs instead of flags.