Boss Spawner v4

//ZoriaRPG
//Spawn an npc that never returns after death.
//Set 'Run on Screen Init to TRUE.
//v4 -6th March, 2018

const int NPC_MISC_BOSS_SPAWN_BIT_INDEX = 15; //The Misc[ index to use for this script.
const int BOSS_SPAWN_SCREEN_D_BIT = 1;
const int BOSS_SPAWN_SCREEN_D_REG = 1;
ffc script spawn_boss {
    void run( int enem_id, int reg, int bit )
    //D0: THe ID of the enemy
    //D1: A Screen->D register. Should be unique for this screen. Valid range is 0 to 7.
    //D2: THe bit of the register. Should be unque per instance of this FFC on the screen.
    //  This is a bit value, in decimal, so use powers of two.
    //  The first instance of the ffc is 1, then 2, then 4, 8, 16.
    {
    if ( reg < 1 || reg > 7 ) reg = BOSS_SPAWN_SCREEN_D_REG;
    if ( bit < 1 || bit > 16 ) bit = BOSS_SPAWN_SCREEN_D_BIT;
        int q; npc n;
        if ( GetScreenDBit(reg,bit) )
        {
            this->Data = 0; Quit();
        }

    //close the shutters
    for ( q = 0; q < 4; q++ )
    {
        if ( Screen->Door[q] == D_OPEN )
        {
            //play shutter sound
            Game->PlaySound(9);
            //close shutter
            Screen->Door[q] = D_SHUTTER;


        }
    }
        //Waitframes(5); //not here!

        n = Screen->CreateNPC(enem_id);
        n->X = this->X; n->Y = this->Y; //Spawn the npc at the ffc coordinates.

    Waitframes(5); //here!

        while(NPCsAlive())
        {
            //While this npc is alive, loop.
            Waitframe();
        }
        //this boss is dead.
        SetScreenDBit(reg,bit,true); //Set the bit so that it never respawns.
    //open the shutters
    //close the shutters
    for ( q = 0; q < 4; q++ )
    {
        if ( Screen->Door[q] == D_SHUTTER )
        {
            //play shutter sound
            Game->PlaySound(9);
            //close shutter
            Screen->Door[q] = D_OPEN;
        }
    }
        this->Data = 0; Quit(); //Clean up the ffc and free it.
    }
}

bool NPCsAlive()
{
    bool alive = false;
    for ( int q = Screen->NumNPCs(); q > 0; --q )
    {
        npc n = Screen->LoadNPC(q);
        if ( n->Type != NPCT_PROJECTILE )
        {
            if ( !(n->MiscFlags&NPCMF_NOT_BEATABLE) )
            {
                if ( n->Type != NPCT_FAIRY )
                {
                    if ( n->Type != NPCT_GUY )
                    {
                        alive = true;
                    }
                }
            }
        }
    }
    return alive;
}