[ASLayoutTransition] Default transition uses snapshots, so that subnodes of each node can't animate independently.

[garrettmoon]

From @ikhromov on December 19, 2016 21:0

I tried to apply animation to ASDisplayNode that has several subnodes.

• (ASLayoutSpec )layoutSpecThatFits:(ASSizeRange)constrainedSize
  {
  / Layout foreground elements in horizontal stack */
  ASStackLayoutSpec *footerHorizontalStack = [ASStackLayoutSpec horizontalStackLayoutSpec];
  [footerHorizontalStack setJustifyContent:ASStackLayoutJustifyContentStart];
  [footerHorizontalStack setAlignItems:ASStackLayoutAlignItemsCenter];

  NSMutableArray *stackItems = [[NSMutableArray alloc] initWithCapacity:3];
  [stackItems addObjectsFromArray:@[__unitsCountTextNode,
  __progressPercentTextNode,
  __progressBar]];
  ....

One of the subnodes __progressBar has it's own subnodes:

• (ASLayoutSpec *)layoutSpecThatFits:(ASSizeRange)constrainedSize
  {
  __backgroundBlueImageNode.style.width = ASDimensionMakeWithFraction([self progressPercent]);
  __backgroundBlueImageNode.style.minWidth = ASDimensionMakeWithFraction([self progressPercent]);
  __backgroundBlueImageNode.style.maxWidth = ASDimensionMakeWithFraction([self progressPercent]);

  ASRelativeLayoutSpec *relativeSpec =
  [ASRelativeLayoutSpec
  relativePositionLayoutSpecWithHorizontalPosition:ASRelativeLayoutSpecPositionStart
  verticalPosition:ASRelativeLayoutSpecPositionStart
  sizingOption:ASRelativeLayoutSpecSizingOptionDefault
  child:__backgroundBlueImageNode];

  ASOverlayLayoutSpec *overlayBlueImageSpec =
  [ASOverlayLayoutSpec overlayLayoutSpecWithChild:__backgroundGrayImageNode
  overlay:relativeSpec];
  return
  [ASBackgroundLayoutSpec backgroundLayoutSpecWithChild:__frontImageNode
  background:overlayBlueImageSpec];
  }

So when I make some changes in parent node and call
[self transitionLayoutWithAnimation:YES
shouldMeasureAsync:NO measurementCompletion:^{}];

1. It will animate only it's own subnodes and subnodes of __progressBar are not animated.
2. Animation will cause snapshots using for ASImageNode subnodes, that is not looks cool.

I think it's a good reason to provide mechanism to animate subnodes in hierarchy, because UIKit does it by default.

Copied from original issue: facebookarchive/AsyncDisplayKit#2804

[garrettmoon]

From @appleguy on December 19, 2016 21:2

As a feature improvement, the default behavior should support recursively applying a new layout. The snapshot feature could be either removed or made available as an optional optimization.