Parallax animation lasting from onEnter until onLeave

[fredconv]

Hello

Thanks to scrollMagic, i was able to create a parallax effect for some background images.
But my background parallax animation only last until my section is completly visible

var section_bg_ctrl = new ScrollMagic.Controller();
var bg_TL = new TimelineMax();
bg_TL
  .from('#parallax .bg', 1, {y: '-40%', ease: Linear.easeNone});
var section1_bg = new ScrollMagic.Scene({
  triggerElement: '.parallax--2',
  triggerHook: 1,
  duration: '100%'
})
  .setTween(bg_TL)
  .addTo(section_bg_ctrl_in);

So here as soon as my parallax section enter the viewport, the tween is triggered.

But how can i make it last until my section is outside the viewport (leaving by the top) and not fully visible ? should i modify the triggerHook with something specific ? or create another Scene and calling a second tween just to handle the leaving of my section ?

and what about performance ?

thanks for your help