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[render] cleanup and comments

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Pierre-Yves Gérardy 2018-05-22 18:30:55 +02:00 • committed by Pierre-Yves Gérardy
parent 144ce68192
commit 285cb5382f
2 changed files with 69 additions and 53 deletions
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119
render/render.js
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@ -200,39 +200,47 @@ module.exports = function($window) {
// ## Diffing
//
// If one list is keyed and the other is unkeyed, the old is removed, and the new one is
// inserted (since the keys are guaranteed to differ).
// Reading https://github.com/localvoid/ivi/blob/ddc09d06abaef45248e6133f7040d00d3c6be853/packages/ivi/src/vdom/implementation.ts#L617-L837
// may be good for context on longest increasing subsequence-based logic for moving nodes.
//
// Then comes the unkeyed diff algo, and at last, the keyed diff algorithm that is split
// in four parts (simplifying a bit).
// In order to diff keyed lists, one has to
//
// The first part goes through both lists top-down as long as the nodes at each level have
// the same key.
// 1) match nodes in both lists, per key, and update them accordingly
// 2) create the nodes present in the new list, but absent in the old one
// 3) remove the nodes present in the old list, but absent in the new one
// 4) figure out what nodes in 1) to move in order to minimize the DOM operations.
//
// The second part deals with lists reversals, and traverses one list top-down and the other
// bottom-up (as long as the keys match).
// To achieve 1) one can create a dictionary of keys => index (for the old list), then iterate
// over the new list and for each new vnode, find the corresponding vnode in the old list using
// the map.
// 2) is achieved in the same step: if a new node has no corresponding entry in the map, it is new
// and must be created.
// For the removals, we actually remove the nodes that have been updated from the old list.
// The nodes that remain in that list after 1) and 2) have been performed can be safely removed.
// The fourth step is a bit more complex and relies on the longest increasing subsequence (LIS)
// algorithm.
//
// The third part goes through both lists bottom up as long as the keys match.
// the longest increasing subsequence is the list of nodes that can remain in place. Imagine going
// from `1,2,3,4,5` to `4,5,1,2,3` where the numbers are not necessarily the keys, but the indices
// corresponding to the keyed nodes in the old list (keyed nodes `e,d,c,b,a` => `b,a,e,d,c` would
// match the above lists, for example).
//
// The first and third sections allow us to deal efficiently with situations where one or
// more contiguous nodes were either inserted into, removed from or re-ordered in an otherwise
// sorted list. They may reduce the number of nodes to be processed in the fourth section.
// In there are two increasing subsequences: `4,5` and `1,2,3`, the latter being the longest. We
// can update those nodes without moving them, and only call `insertNode` on `4` and `5`.
//
// The fourth section does keyed diff for the situations not covered by the other three. It
// builds a {key: oldIndex} dictionary and uses it to find old nodes that match the keys of
// new ones.
// The nodes from the `old` array that have a match in the new `vnodes` one are removed from
// the old list (set to `null`).
// @localvoid adapted the algo to also support node deletions and insertions (the `lis` is actually
// the longest increasing subsequence *of old nodes still present in the new list*).
//
// If there are still nodes in the new `vnodes` array that haven't been matched to old ones,
// they are created.
// The range of old nodes that wasn't covered by the first three sections is passed to
// `removeNodes()`. The nodes that remain in the list are removed from the DOM.
// It is a general algorithm that is fireproof in all circumstances, but it requires the allocation
// and the construction of a `key => oldIndex` map, and three arrays (one with `newIndex => oldIndex`,
// the `LIS` and a temporary one to create the LIS).
//
// So we cheat where we can: if the tails of the lists are identical, they are guaranteed to be part of
// the LIS and can be updated without moving them.
//
// If two nodes are swapped, they are guaranteed not to be part of the LIS, and must be moved (with
// the exception of the last node if the list is fully reversed).
//
// It should be noted that the description of the four sections above is not perfect, because those
// parts are actually implemented as only two loops, one for the first two parts, and one for
// the other two. I'm not sure it wins us anything except maybe a few bytes of file size.
// ## Finding the next sibling.
//
// `updateNode()` and `createNode()` expect a nextSibling parameter to perform DOM operations.
@ -301,6 +309,7 @@ module.exports = function($window) {
// keyed diff
var oldEnd = old.length - 1, end = vnodes.length - 1, map, o, v, oe, ve, topSibling
// bottom-up
while (oldEnd >= oldStart && end >= start) {
oe = old[oldEnd]
ve = vnodes[end]
@ -314,6 +323,7 @@ module.exports = function($window) {
break
}
}
// top-down
while (oldEnd >= oldStart && end >= start) {
o = old[oldStart]
v = vnodes[start]
@ -326,11 +336,8 @@ module.exports = function($window) {
break
}
}
//swaps and list reversals
// swaps and list reversals
while (oldEnd >= oldStart && end >= start) {
o = old[oldStart]
v = vnodes[start]
if (o == null) oldStart++
else if (v == null) start++
else if (oe == null) oldEnd--
@ -348,7 +355,10 @@ module.exports = function($window) {
}
oe = old[oldEnd]
ve = vnodes[end]
o = old[oldStart]
v = vnodes[start]
}
// bottom up once again
while (oldEnd >= oldStart && end >= start) {
if (oe == null) oldEnd--
else if (ve == null) end--
@ -365,47 +375,48 @@ module.exports = function($window) {
if (start > end) removeNodes(old, oldStart, oldEnd + 1)
else if (oldStart > oldEnd) createNodes(parent, vnodes, start, end + 1, hooks, nextSibling, ns)
else {
// inspired by ivi
var originalNextSibling = nextSibling, vnodesLength = end - start + 1, map, i, lis
var oldIndices = new Array(end - start + 1)
// inspired by ivi https://github.com/ivijs/ivi/ by Boris Kaul
var originalNextSibling = nextSibling, vnodesLength = end - start + 1, oldIndices = new Array(vnodesLength), li=0, i=0, pos = 2147483647, matched = 0, map, lisIndices
for (i = 0; i < vnodesLength; i++) oldIndices[i] = -1
var pos = 2147483647, matched = false
for (i = end; i >= start; i--) {
if (map == null) map = getKeyMap(old, oldStart, oldEnd + 1)
v = vnodes[i]
if (v != null) {
var oldIndex = map[v.key]
ve = vnodes[i]
if (ve != null) {
var oldIndex = map[ve.key]
if (oldIndex != null) {
pos = (oldIndex < pos) ? oldIndex : -1 // becomes -1 if nodes were re-ordered
oldIndices[i-start] = oldIndex
o = old[oldIndex]
oe = old[oldIndex]
old[oldIndex] = null
if (o !== v) updateNode(parent, o, v, hooks, nextSibling, ns)
if (v.dom != null) nextSibling = v.dom
matched = true
if (oe !== ve) updateNode(parent, oe, ve, hooks, nextSibling, ns)
if (ve.dom != null) nextSibling = ve.dom
matched++
}
}
}
nextSibling = originalNextSibling
removeNodes(old, oldStart, oldEnd + 1)
if (!matched) createNodes(parent, vnodes, start, end + 1, hooks, nextSibling, ns)
if (matched !== oldEnd - oldStart + 1) removeNodes(old, oldStart, oldEnd + 1)
if (matched === 0) createNodes(parent, vnodes, start, end + 1, hooks, nextSibling, ns)
else {
if (pos === -1) {
lis = makeLis(oldIndices)
var lisi = lis.length - 1
// the indices of the indices of the items that are part of the
// longest increasing subsequence in the oldIndices list
lisIndices = makeLisIndices(oldIndices)
li = lisIndices.length - 1
for (i = end; i >= start; i--) {
if (oldIndices[i-start] === -1) createNode(parent, vnodes[i], hooks, ns, nextSibling)
v = vnodes[i]
if (oldIndices[i-start] === -1) createNode(parent, v, hooks, ns, nextSibling)
else {
if (lis[lisi] === i - start) lisi--
else insertNode(parent, toFragment(vnodes[i]), nextSibling)
if (lisIndices[li] === i - start) li--
else insertNode(parent, toFragment(v), nextSibling)
}
if (vnodes[i].dom != null) nextSibling = vnodes[i].dom
if (v.dom != null) nextSibling = vnodes[i].dom
}
} else {
for (i = end; i >= start; i--) {
if (oldIndices[i-start] === -1) createNode(parent, vnodes[i], hooks, ns, nextSibling)
if (vnodes[i].dom != null) nextSibling = vnodes[i].dom
v = vnodes[i]
if (oldIndices[i-start] === -1) createNode(parent, v, hooks, ns, nextSibling)
if (v.dom != null) nextSibling = vnodes[i].dom
}
}
}
@ -522,7 +533,11 @@ module.exports = function($window) {
return map
}
// Lifted from ivi https://github.com/ivijs/ivi/
function makeLis(a) {
// takes a list of unique numbers (-1 is special and can
// occur multiple times) and returns an array with the indices
// of the items that are part of the longest increasing
// subsequece
function makeLisIndices(a) {
var p = a.slice()
var result = []
result.push(0)