Event Draw
GML
draw_rectangle_color(view_xview,view_yview,view_xview+100,view_yview+16,c_red,c_white,c_blue,c_black,true);
draw_rectangle_color(view_xview,view_yview,view_xview+global.hp,view_yview+16,c_red,c_red,c_red,c_white,false);
gdzie global.hp to Twoja zmienna hp bohatera..