My BG

let bSpell = false;
let GCSD = GetCurrentScriptDirectory();
let bg1 = GCSD~"img/spell.png";//spell
LoadTexture(bg1);
let bg2 = GCSD~"img/non.png";//nonspell
LoadTexture(bg2);

@Initialize{
	TCallBg;
}

@MainLoop{
	let objScene=GetEnemyBossSceneObjectID();
	if(objScene!=ID_INVALID&&ObjEnemyBossScene_GetInfo(objScene,INFO_IS_SPELL)) {
		bSpell=true;
	}else {
		bSpell=false;
	}
	yield;
}

task TCallBg{
	while(!Obj_IsDeleted(GetEnemyBossSceneObjectID())){
		if(bSpell==false){
			TNormalBackground;
		}
		while(bSpell==false){ yield; }
			if(bSpell==true){
				TSpellBackground;
			}
		while(bSpell==true){ yield; }
    }
}

task TNormalBackground{
	let obj = ObjPrim_Create(OBJ_SPRITE_2D);
	ObjRender_SetBlendType(obj,BLEND_ALPHA);
	Obj_SetRenderPriority(obj,0.21);
	ObjPrim_SetTexture(obj,bg2);
	ObjSprite2D_SetSourceRect(obj,0,0,256,256);
	ObjSprite2D_SetDestCenter(obj);
	ObjRender_SetScaleXYZ(obj,512/256,512/256,1);
	ObjRender_SetX(obj,GetStgFrameWidth()/2);
	ObjRender_SetY(obj,GetStgFrameHeight()/2);
}

task TSpellBackground{
	let obj = ObjPrim_Create(OBJ_SPRITE_2D);
	ObjRender_SetBlendType(obj,BLEND_ALPHA);
	Obj_SetRenderPriority(obj,0.21);
	ObjPrim_SetTexture(obj,bg1);
	ObjSprite2D_SetSourceRect(obj,0,0,384,448);
	ObjSprite2D_SetDestCenter(obj);
	ObjRender_SetScaleXYZ(obj,512/384,512/448,1);
	ObjRender_SetX(obj,GetStgFrameWidth()/2);
	ObjRender_SetY(obj,GetStgFrameHeight()/2);
}