Parent animator offset via private API

controllers.application.js

import Ember from 'ember';
import move from 'ember-animated/motions/move';
import { fadeIn, fadeOut } from 'ember-animated/motions/opacity';
import { easeIn, easeOut, easeInAndOut } from 'ember-animated/easings/cosine';

export default Ember.Controller.extend({
  appName: 'Ember Twiddle',
  
  isThingActive: false,
  
  showThingActions: true,
  
  duration: 1500,
  
  things: null,
  
  init() {
  	this.set('things', this.makeItems(2));
    console.log(this.get('things'));
    this.initialThings = [...this.things];
  },
  
  actions: {
  	activate(thing) {
      this.set('selectedThing', thing.id);
      this.get('things').reverseObjects();
    }
  },
  
  // manages vertical motion during list sorting
  *transition({ keptSprites, duration }) {
		// console.log(arguments[0]);
  	for (let sprite of keptSprites) {
    	move(sprite, { duration, easing: easeOut });
    }
	},
  
  // manages icons sliding in/out of list items
	*iconTransition({ insertedSprites, keptSprites, removedSprites, duration }) {
  	
   	// a slight slide in from the right
    for (let sprite of insertedSprites) {
      sprite.startTranslatedBy(50, 0);
    	move(sprite, { duration, easing: easeOut });
  		// fadeIn(sprite);
    }
    
    // handle interruption
    for (let sprite of keptSprites) {
    	move(sprite, { duration, easing: easeOut });
  		// fadeIn(sprite);
    }
  
    // a slight slide out to the right
  	for (let sprite of removedSprites) {
      sprite.endTranslatedBy(50, 0);
    	move(sprite, { duration, easing: easeIn });
  		// fadeOut(sprite);
    }
	},
    
      // manages icons sliding in/out of list items
	*iconTransitionWithOffset({ insertedSprites, keptSprites, removedSprites, duration }) {
    
    // a slight slide in from the right
  	for (let sprite of insertedSprites) {
      let offsetDy = 0
      
      // WARNING: this is private API.
      let offsetSprite = sprite._offsetSprite;
      if (offsetSprite) {
      	offsetDy = offsetSprite.initialBounds.top - offsetSprite.finalBounds.top;
      }
      
      sprite.startTranslatedBy(50, -offsetDy);
    	move(sprite, { duration, easing: easeOut });
  		// fadeIn(sprite);
    }
    
    // handle interruption
    for (let sprite of keptSprites) {
    	move(sprite, { duration, easing: easeOut });
  		// fadeIn(sprite);
    }
  
    // a slight slide out to the right
  	for (let sprite of removedSprites) {
      sprite.endTranslatedBy(50, 0);
    	move(sprite, { duration, easing: easeIn });
  		// fadeOut(sprite);
    }
	},

  makeItems(count = 5) {
    let result = Ember.A();
    for (let i = 0; i < count; i++) {
      result.push(makeRandomItem(i));
    }
    return (result);
  },
});

function makeRandomItem(index) {
  var messages = ["Dwight", "Stanley", "Kelly", "Ryan", "Kevin"];
  var images = ['https://pbs.twimg.com/profile_images/549268771484229632/WnatiHzT_400x400.jpeg', 'https://pbs.twimg.com/profile_images/1839546020/florida_stanley_400x400.jpg', 'https://pbs.twimg.com/profile_images/71405458/2928282474_24807334d7_400x400.jpg', 'https://pbs.twimg.com/profile_images/740436182107049984/y0N8Sqbi_400x400.jpg', 'https://pbs.twimg.com/profile_images/118888142/Brian_Baumgartner_134198_400x400.jpg'];
  return { id: index, message: messages[index], image: images[index] };
}

styles.app.css

body {
  margin: 12px 16px;
  font-family: 'Helvetica Neue', Helvetica, Arial, sans-serif;
  font-size: 12pt;
}

.thing {
  width: 50vw;
  padding: 1rem;
  margin: 0.5rem 0;
  color: white;
	background: steelblue;
  display: flex;
  justify-content: space-between;
  align-items: center;
  cursor: pointer;
/*   overflow: hidden; */
}

.icons {

}

templates.application.hbs

<h1>Nested Animator Offset</h1>

<h2>Simple Example</h2>
<p>Single animator that slides and fades icons. <br>This is the end goal for the icons in the nested example below.</p>

<div class="thing {{if isThingActive 'is-active'}}" {{action (mut isThingActive) (not isThingActive)}}>

  <p>Some little thing (click me).</p>

  {{#animated-if isThingActive use=iconTransition duration=duration}}
  	<div class="activeIcons">✅</div>
  {{else}}
  	<div class="activeIcons">❎</div>
  {{/animated-if}}

</div>

<hr/>

<h2>Nested Example</h2>
<p>Nested animator that slides and fades icons.</p>

<p><strong>⬇️ Click any item to flip the list sorting</strong> and select that item. <br>Notice the inserted icons' starting position is offset by some amount and is not synced with the parent animator vertical motion.</p>

<p>The vertical movement is simply the list sort order changing.</p>

<p>Selected Thing ID: <code>{{selectedThing}}</code></p>

<AnimatedContainer>
	{{#animated-each things key="id" use=transition duration=duration as |thing|}}
  <div class="thing" {{action 'activate' thing}}>
    
    <p>[{{thing.id}}] {{thing.message}}</p>
		
    <AnimatedContainer>
      {{#animated-if (eq thing.id selectedThing) use=iconTransition duration=duration}}
        <div class="icons enabled">✅</div>
      {{else}}
        <div class="icons disabled">❎</div>
      {{/animated-if}}
    </AnimatedContainer>

	</div>
  {{/animated-each}}
</AnimatedContainer>

<hr/>

<h2>Nested Example with Adjusted Offset</h2>
<p>Here, the icon transition uses the private API of <code>sprite._offsetParent</code> to account for the changing vertical position of the parent animator.</p>

<p><strong>⬇️ Click the first item</strong> and notice that the inserted icons now properly follow the parent animator vertical motion.</p>

<p>Selected Thing ID: <code>{{selectedThing}}</code></p>

<AnimatedContainer>
	{{#animated-each things key="id" use=transition duration=duration as |thing|}}
  <div class="thing" {{action 'activate' thing}}>
    
    <p>[{{thing.id}}] {{thing.message}}</p>
		
    <AnimatedContainer>
      {{#animated-if (eq thing.id selectedThing) use=iconTransitionWithOffset duration=duration}}
        <div class="icons enabled">✅</div>
      {{else}}
        <div class="icons disabled">❎</div>
      {{/animated-if}}
    </AnimatedContainer>

	</div>
  {{/animated-each}}
</AnimatedContainer>

<br>
<br>
{{outlet}}
<br>
<br>

twiddle.json

{
  "version": "0.15.1",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.js",
    "ember": "3.4.3",
    "ember-template-compiler": "3.4.3",
    "ember-testing": "3.4.3"
  },
  "addons": {
    "ember-animated": "0.6.1",
    "ember-truth-helpers": "2.1.0"
  }
}