1# Release Notes
2
3## Unreleased
4
5### Breaking
6
7#### Measure function changes
8
9The "measure function" API for integrating Taffy with other measurement systems (such as text layout) has been changed to be more flexible,
10and to interact better with borrow checking (you can now borrow external data in your measure function!).
11
12- There are no longer per-node measure functions.
13- There is now a single "global" measure function, and a per-node "context" of a user-defined type
14- The `Taffy` tree is now a generic `Taffy<T>` where `T` is the "context" type.
15
16If you are not using measure functions, then the only change you will need to make is from:
17
18```rust
19let mut tree = Taffy::new();
20```
21
22to
23
24```rust
25let mut tree : Taffy<()> = Taffy::new();
26```
27
28And generally update any uses of `Taffy` in your codebase to `Taffy<()>`.
29
30If you are using measure functions then you will need to make some bigger (but straightforward) changes. The following Taffy 0.3 code:
31
32```rust
33let mut tree = Taffy::new();
34let leaf = tree.new_leaf_with_measure(
35  Style::DEFAULT,
36  |known_dimensions: Size<Option<f32>>, available_space: Size<AvailableSpace>| Size { width: 100.0, height: 200.0 }
37);
38tree.compute_layout(leaf, Size::MAX_CONTENT);
39```
40
41Should become something like the following with Taffy 0.4:
42
43```rust
44let mut tree : Taffy<Size> = Taffy::new();
45let leaf = tree.new_leaf_with_context(Style::DEFAULT, Size { width: 100.0, height: 200.0 });
46tree.compute_layout_with_measure(
47  leaf,
48  Size::MAX_CONTENT,
49  |known_dimensions: Size<Option<f32>>, available_space: Size<AvailableSpace>, node_id: NodeId, node_context: Option<Size>| {
50    node_context.unwrap_or(Size::ZERO)
51  }
52);
53```
54
55Note that:
56
57- You can choose any type instead of `Size` in the above example. This includes your own custom type (which can be an enum or a trait object).
58- If you don't need a context then you can use `()` for the context type
59- As the single "global" measure function passed to `compute_layout_with_measure` only needs to exist for the duration of a single layout run,
60  it can (mutably) borrow data from it's environment
61
62#### Many APIs have been renamed to replace `points` or `Points` with `length` or `Length`
63
64This new name better describes one-dimentional measure of space in some unspecified unit
65which is often unrelated to the PostScript point or the CSS `pt` unit.
66
67This also removes a misleading similarity with the 2D `Point`,
68whose components can have any unit and are not even necessarily absolute lengths.
69
70Example usage change:
71
72```diff
73 use taffy::prelude::*;
74
75 // …
76
77 let header_node = taffy
78     .new_leaf(
79         Style {
80-            size: Size { width: points(800.0), height: points(100.0) },
81+            size: Size { width: length(800.0), height: length(100.0) },
82             ..Default::default()
83         },
84     ).unwrap();
85```
86
87### Added
88
89- Support for [CSS Block layout](https://developer.mozilla.org/en-US/docs/Web/CSS/CSS_Flow_Layout/Block_and_Inline_Layout_in_Normal_Flow#elements_participating_in_a_block_formatting_context) has been added. This can be used via the new `Display::Block` variant of the `Display` enum. Note that inline, inline-block and float have *not* been implemented. The use case supported is block container nodes which contain block-level children.
90- Support for running each layout algorithm individually on a single node via the following top-level functions:
91  - `compute_flexbox_layout`
92  - `compute_grid_layout`
93  - `compute_leaf_layout`
94  - `compute_hidden_layout`
95- Added `insert_child_at_index()` method to the `Taffy` tree. This can be used to insert a child node at any position instead of just the end.
96
97### Removed
98
99- `layout_flexbox()` has been removed from the prelude. Use `taffy::compute_flexbox_layout` instead.
100- The following methods have been removed from the `LayoutTree` trait: `parent`, `is_childless`, `measure_node`, `needs_measure`, and `mark_dirty`. These no longer need to be implemented in custom implementations of `LayoutTree`.
101
102### Changes
103
104- The Flexbox algorithm has now been moved behind the `flexbox` feature. The `flexbox` feature is enabled by default.
105- The `justify_self` property has been moved behind the `grid` feature.
106- `taffy::node::Node` has been replaced with `taffy::tree::NodeId`. This should make it much easier to implement the `LayoutTree` trait as the underlying type backing the node id now a `u64` rather than a `slotmap::DefaultKey`.
107- Module organisation changes:
108  - The `math` module has been made private
109  - The `axis` module has been merged into the `geometry` module
110  - The debug module is no longer public. The `print_tree` function is now accesible under `util`.
111  - All types from the `node`, `data`, `layout`, `error` and `cache` modules have been moved to the  the `tree` module.
112- Fixed misspelling: `RunMode::PeformLayout` renamed into `RunMode::PerformLayout` (added missing `r`).
113
114## 0.3.16
115
116### Fixes
117
118- Improve performance of flexbox columns
119
120## 0.3.15
121
122### Fixes
123
124- Fix justify-content and align-content when free space is negative (content overflows container) (#549) (#551)
125
126## 0.3.14
127
128### Fixes
129
130- Flex: Fix issue where constraints were not being propagated, causing nodes with inherent aspect-ratio (typically images) to not apply that aspect-ratio (#545) (Fixes bevyengine/bevy#9841)
131
132## 0.3.13
133
134### Fixes
135
136- Fix rounding accumulation bug (#521) (Fixes #501 and bevyengine/bevy#8911)
137- Flexbox: pass correct cross-axis available space when computing an item's intrinsic main size (#522)(Fixes bevyengine/bevy#9350)
138- Flexbox: Subtract child margin not parent margin when computing stretch-alignment known size
139- Grid: Make CSS Grid algorithm correctly apply max width/height and available space when it is the root node (#491)
140- Grid: Fix CSS Grid "auto track" / placement bugs #481
141  - Fix divide by zero when using grid_auto_rows/grid_auto_columns with zero negative implicit tracks
142  - Fix over counting of tracks (leading to incorrect container heights) when auto-placing in grids that contain negative implicit tracks.
143  - Fix axis conflation in auto-placement code when grid_auto_flow is column
144  - Fix assignment of auto track sizes when initializing negative implicit tracks
145- Leaf: Apply margins to leaf nodes when computing available space for measure functions
146- Leaf: Reserve space for padding/borders in nodes with measure functions (#497)
147  
148  **NOTE: This has the potential to break layouts relying on the old behaviour.** However, such layouts would be relying on a style having no effect, so it is judged that such layouts are unlikely to exist in the wild. If this turns out not to be true then this fix will be reverted on the 0.3.x branch.
149
150### Dependencies
151
152- Upgrade `grid` to `0.10`. This eliminates the transitive dependency on `no-std-compat`.
153
154## 0.3.12
155
156### Fixes
157
158- Fix caching issue when toggling `display:none` on and off
159
160## 0.3.11
161
162### Fixes
163
164- Fix exponential blowup when laying out trees containing nodes with min and max sizes.
165
166## 0.3.10
167
168### Fixes
169
170- Fix sizing of children when the available_space < min_size (#407)
171
172## 0.3.9
173
174### Fixes
175
176- Fix caching bug where a cached result would sometimes be incorrectly used when the amount of available space increased (bevyengine/bevy#8111) and (bevyengine/bevy#8124)
177
178## 0.3.8
179
180### Fixes
181
182- Fix incorrect min-content size for `flex-wrap: wrap` nodes (bevyengine/bevy#8082)
183
184## 0.3.7
185
186### Fixes
187
188- Fix: Make `padding` and `border` floor node sizes (#372)
189- Fix: Prevent percentages contributing to min-content sizes (#388) (also fixes bevyengine/bevy#8017)
190
191## 0.3.6
192
193### Fixes
194
195- Fix: Ignore `align_content` when `flex_wrap` is set to `nowrap` (#383)
196
197## 0.3.5
198
199### Fixes
200
201- Fix `display: none` when it is set on a flexbox child (#380)
202- Fix `display: none` when it is set on a grid child (#381)
203
204## 0.3.4
205
206### Fixes
207
208- Fix `display: none` when it is set for the only node in the hierarchy (#377)
209
210## 0.3.3
211
212### Added
213
214- Added `enable_rounding` and `disable_rounding` methods to the `Taffy` struct which enable consumers of Taffy to obtain unrounded `f32` values for the computed layouts if they want them. Rounding remains enabled by default.
215
216### Fixes
217
218- Fixed rounding algorithm such that it never leaves gaps between adjacent nodes (#369)
219- Fixed compiling with the `grid` feature disabled (#370)
220- Fixed compiling with the `std` feature disabled
221
222## 0.3.2
223
224### Fixes
225
226- Allow partial nested values to be deserialized into a `Style` using the `serde` feature.
227
228## 0.3.1
229
230### Fixes
231
232- The `serde` feature now works when the `grid` feature is enabled
233
234## 0.3.0
235
236### Highlights
237
238- [CSS Grid algorithm support](#new-feature-css-grid)
239- [Style helper functions](#new-feature-style-helpers)
240
241See below for details of breaking changes.
242
243### New Feature: CSS Grid
244
245We very excited to report that we now have support for CSS Grid layout. This is in addition to the existing Flexbox layout support, and the two modes interoperate. You can set a node to use Grid layout by setting the `display` property to `Display::Grid`.
246
247#### Learning Resources
248
249Taffy implements the CSS Grid specification faithfully, so documentation designed for the web should translate cleanly to Taffy's implementation. If you are interested in learning how to use CSS Grid, we would recommend the following resources:
250
251- [CSS Grid Garden](https://cssgridgarden.com/). This is an interactive tutorial/game that allows you to learn the essential parts of CSS Grid in a fun engaging way.
252- [A Complete Guide To CSS Grid](https://css-tricks.com/snippets/css/complete-guide-grid/) by CSS Tricks. This is detailed guide with illustrations and comphrehensive written explanation of the different Grid propertie and how they work.
253
254#### Supported Features & Properties
255
256In addition to the usual sizing/spacing proerties (size, min_size, padding, margin, etc), the following Grid style properties are supported on Grid Containers:
257
258| Property                  | Explanation                                                                                    |
259| ---                       | ---                                                                                            |
260| [`grid-template-columns`] | The track sizing functions of the grid's explicit columns                                      |
261| [`grid-template-rows`]    | The track sizing functions of the grid's explicit rows                                         |
262| [`grid-auto-rows`]        | Track sizing functions for the grid's implicitly generated rows                                |
263| [`grid-auto-columns`]     | Track sizing functions for the grid's implicitly generated columns                             |
264| [`grid-auto-flow`]        | Whether auto-placed items are placed row-wise or column-wise. And sparsely or densely.         |
265| [`gap`]                   | The size of the vertical and horizontal gaps between grid rows/columns                         |
266| [`align-content`]         | Align grid tracks within the container in the inline (horizontal) axis                         |
267| [`justify-content`]       | Align grid tracks within the container in the block (vertical) axis                            |
268| [`align-items`]           | Align the child items within their grid areas in the inline (horizontal) axis                  |
269| [`justify-items`]         | Align the child items within their grid areas in the block (vertical) axis                     |
270
271And the following Grid style properties are supported on Grid Items (children):
272
273| Property                  | Explanation                                                                                    |
274| ---                       | ---                                                                                            |
275| [`grid-row`]              | The (row) grid line the item starts at (or a span)                                             |
276| [`grid-column`]           | The (column) grid line the item end at (or a span)                                             |
277| [`align-self`]            | Align the item within it's grid area in the inline (horizontal) axis. Overrides `align-items`. |
278| [`justify-self`]          | Align the item within it's grid area in the block (vertical) axis. Overrides `justify-items`.  |
279
280[`grid-template-columns`]: https://developer.mozilla.org/en-US/docs/Web/CSS/grid-template-columns
281[`grid-template-rows`]: https://developer.mozilla.org/en-US/docs/Web/CSS/grid-template-rows
282[`grid-auto-rows`]: https://developer.mozilla.org/en-US/docs/Web/CSS/grid-auto-rows
283[`grid-auto-columns`]: https://developer.mozilla.org/en-US/docs/Web/CSS/grid-auto-columns
284[`grid-auto-flow`]: https://developer.mozilla.org/en-US/docs/Web/CSS/grid-auto-flow
285[`gap`]: https://developer.mozilla.org/en-US/docs/Web/CSS/gap
286[`align-content`]: https://developer.mozilla.org/en-US/docs/Web/CSS/align_content
287[`justify-content`]: https://developer.mozilla.org/en-US/docs/Web/CSS/justify_content
288[`align-items`]: https://developer.mozilla.org/en-US/docs/Web/CSS/align-items
289[`justify-items`]: https://developer.mozilla.org/en-US/docs/Web/CSS/justify-items
290[`grid-row`]: https://developer.mozilla.org/en-US/docs/Web/CSS/grid-row
291[`grid-column`]: https://developer.mozilla.org/en-US/docs/Web/CSS/grid-column
292[`align-self`]: https://developer.mozilla.org/en-US/docs/Web/CSS/align-self
293[`justify-self`]: https://developer.mozilla.org/en-US/docs/Web/CSS/justify-self
294
295The following properties and features are not currently supported:
296
297- Subgrids
298- Masonry grid layout
299- Named grid lines
300- Named areas: `grid-template-areas` and `grid-area`
301- `grid-template` or `grid` shorthand
302
303#### Example
304
305See [examples/grid_holy_grail.rs](https://github.com/DioxusLabs/taffy/blob/main/examples/grid_holy_grail.rs) for an example using Taffy to implement the so-called [Holy Grail Layout](https://en.wikipedia.org/wiki/Holy_grail_(web_design)). If you want to run this example, the don't forget the enable the CSS Grid cargo feature:
306
307```bash
308cargo run --example grid_holy_grail --features grid
309```
310
311### New Feature: Style Helpers
312
313Ten new helper functions have added to the taffy prelude. These helper functions have short, intuitive names, and have generic return types which allow them to magically return the correct type depending on context. They make defining styles much easier, and means you won't typically need to use types like `Dimension` or `TrackSizingFunction` directly.
314
315For example, instead of:
316
317```rust
318let size : Size<Dimension> = Size { width: Dimension::Points(100.0), height: Dimension::Percent(50.0) };
319```
320
321you can now write
322
323```rust
324let size : Size<Dimension> = Size { width: points(100.0), height: percent(50.0) };
325```
326
327And that same helper function will work other types like `LengthPercentage` and `MinTrackSizingFunction` that also have a `Points` variant. There are also generic impl's for `Size<T>`, `Rect<T>` and `Line<T>` which means if your node is the same size in all dimensions you can even write
328
329```rust
330let size : Size<Dimension> = points(100.0);
331```
332
333Available style helpers:
334
335<table>
336  <thead><tr><th>Type(s)</th><th colspan="2">Helpers that work with that type</th></tr></thead>
337  <tbody>
338    <tr>
339      <td rowspan="3"><code>LengthPercentage</code></td>
340      <td><code>zero()</code></td>
341      <td>Generates a <code>Points</code> variant with the value <code>0.0</code></td>
342    </tr>
343    <tr>
344      <td><code>points(val:&nbsp;f32)</code></td>
345      <td>Generates a <code>Points</code> variant with the specified value</td>
346    </tr>
347    <tr>
348      <td><code>percent(val:&nbsp;f32)</code></td>
349      <td>Generates a <code>Percent</code> variant with the specified value.<br />Note that the scale of 0-1 not 0-100.</td>
350    </tr>
351    <tr>
352      <td rowspan="2"><code>LengthPercentageAuto</code><br /><code>Dimension</code></td>
353      <td colspan="2"><i>All helpers from <code>LengthPercentage</code> and...</i></td>
354    </tr>
355    <tr>
356      <td><code>auto()</code></td>
357      <td>Generates an <code>Auto</code> variant</td>
358    </tr>
359    <tr>
360      <td rowspan="3"><code>MinTrackSizingFunction</code></td>
361      <td colspan="2"><i>All helpers from <code>LengthPercentageAuto</code>/<code>Dimension</code> and...</i></td>
362    </tr>
363    <tr>
364      <td><code>min_content()</code></td>
365      <td>Generates an <code>MinContent</code> variant</td>
366    </tr>
367      <tr>
368      <td><code>max_content()</code></td>
369      <td>Generates an <code>MinContent</code> variant</td>
370    </tr>
371    <tr>
372      <td rowspan="3"><code>MaxTrackSizingFunction</code></td>
373      <td colspan="2"><i>All helpers from <code>MinTrackSizingFunction</code> and...</i></td>
374    </tr>
375    <tr>
376      <td><code>fit_content(limit:&nbsp;LengthPercentage)</code></td>
377      <td>Generates a <code>FitContent</code> variant with the specified limit.<br />Nest the <code>points</code> or <code>percent</code> helper inside this function to specified the limit.</td>
378    </tr>
379      <tr>
380      <td><code>fr(fraction:&nbsp;f32)</code></td>
381      <td>Generates a <code>Fraction</code> (<code>fr</code>) variant with the specified flex fraction </td>
382    </tr>
383    <tr>
384      <td rowspan="3"><code>NonRepeatingTrackSizingFunction</code></td>
385      <td colspan="2"><i>All helpers from <code>MaxTrackSizingFunction</code> and...</i></td>
386    </tr>
387    <tr>
388      <td><code>minmax(min: MinTrackSizingFunction, max: MaxTrackSizingFunction)</code></td>
389      <td>Equivalent to CSS <code>minmax()</code> function.</td>
390    </tr>
391    <tr>
392      <td><code>flex(fraction:&nbsp;f32)</code></td>
393      <td>Equivalent to CSS <code>minmax(0px, 1fr)</code>. This is likely what you want if you want evenly sized rows/columns.</td>
394    </tr>
395    <tr>
396      <td rowspan="2"><code>TrackSizingFunction</code></td>
397      <td colspan="2"><i>All helpers from <code>NonRepeatingTrackSizingFunction</code> and...</i></td>
398    </tr>
399    <tr>
400      <td><code>repeat(rep: GridTrackRepetition, tracks: Vec&lt;TrackSizingFunction&gt;)</code></td>
401      <td>Equivalent to css <code>repeat()</code> function.</td>
402    </tr>
403    <tr>
404      <td><code>Vec&lt;TrackSizingFunction&gt;</code></td>
405      <td><code>evenly_sized_tracks(count:&nbsp;u16)</code></td>
406      <td>Equivalent to CSS <code>repeat(count, minmax(0px, 1fr)</code></td>
407    </tr>
408    <tr>
409      <td rowspan="3"><code>AvailableSpace</code></td>
410      <td><code>auto()</code></td>
411      <td>Generates an <code>Auto</code> variant</td>
412    </tr>
413    <tr>
414      <td><code>min_content()</code></td>
415      <td>Generates an <code>MinContent</code> variant</td>
416    </tr>
417      <tr>
418      <td><code>max_content()</code></td>
419      <td>Generates an <code>MinContent</code> variant</td>
420    </tr>
421    <tr>
422      <td><code>Size&lt;T&gt;</code></td>
423      <td colspan="2">Any helper that works for <code>T</code> will also work for <code>Size&lt;T&gt;</code> and will set both <code>width</code> and <code>height</code> to that value</td>
424    </tr>
425    <tr>
426      <td><code>Rect&lt;T&gt;</code></td>
427      <td colspan="2">Any helper that works for <code>T</code> will also work for <code>Rect&lt;T&gt;</code> and will set <code>top</code>, <code>left</code>, <code>bottom</code>, and <code>right</code> to that value</td>
428    </tr>
429  </tbody>
430</table>
431
432### Breaking API changes
433
434#### Changes to alignment style types
435
436- `AlignContent` and `JustifyContent` has been merged.
437  - `JustifyContent` is now an alias of `AlignContent` and contains the `Stretch` variant.
438  - This variant will be *ignored* (falling back to `Start`) when applied Flexbox containers. It is valid value for Grid containers.
439- `AlignItems` and `AlignSelf` have been merged.
440  - The `Auto` variant of `AlignSelf` has been removed. You should now use `Option::None` if you wish to specify `AlignSelf::Auto`.
441  - `AlignSelf` is now an alias of `AlignItems`.
442  - `JustifyItems` and `JustifySelf` aliases have been added. These properties have no affect on Flexbox containers, but apply to Grid containers.
443- `Default` impls have been removed from all alignment types. This is because the correct default varies by property, and the types are now shared between multiple properties. The `Style` struct still has a default for each alignment property, so this is considered unlikely to affect you in practice.
444
445#### Strict style types
446
447- New types `LengthPercentage` and `LengthPercentageAuto` have been added.
448  - `LengthPercentage` is like `Dimension` but only contains the `Points` and `Percent` variants, which allows us to increase type safety for properties that don't support the `Auto` value.
449  - `LengthPercentageAuto` is currently identical to `Dimension` but will allow us to expand dimension in future to support values like `MinContent`, `MaxContent` and `FitContent`.
450- Some style properties have been updated to use either `LengthPercentage` or `LengthPercentageAuto` instead of `Dimension`. You will need to update your code, but it is recommended that you use the new style helpers (see above) rather than using the new types directly (although you certainly can use them directly if you want to).
451
452#### Position properties renamed
453
454- The `position` property is now renamed to `inset` and is now in line with [CSS inset specs](https://developer.mozilla.org/en-US/docs/Web/CSS/inset)
455- The `position_type` property is now renamed to `position` and is now in line with [CSS position specs](https://developer.mozilla.org/en-US/docs/Web/CSS/position). The `PositionType` enum has been similarly renamed to `Position`.
456
457#### Changes to `LayoutTree`
458
459- Added generic associated type to `LayoutTree` for a `ChildIter`, an iterator on the children of a given node.
460- Changed the `children` method of `LayoutTree` to return the `ChildIter` generic associated type to allow for custom tree storage implementations which do not store the children of a node contiguously.
461- Added `child_count`  method to `LayoutTree` for querying the number of children of a node. Required because the `children` method now returns an iterator instead of an array.
462- Added `is_childless` method to `LayoutTree` for querying whether a node has no children.
463
464#### `AvailableSpace` has been moved
465
466The `AvailableSpace` enum has been moved from the `layout` module to the `style` module. If you are importing it via the prelude then you will unaffected by the change.
467
468### Fixes
469
470- Flexbox nodes sized under a min-content constraint now size correctly (#291)
471- Aspect ratio is now applied correctly in many circumstances
472- Absolutely positioned items now apply margins correctly
473- Min/max size are now applied correctly
474- Inset applied incorrectly to relatively positioned flexbox children when both `top` and `bottom` or `left` and `right` were specified (#348)
475- Fix case where column-gap style could be used in place of row-gap style (when using a percentage gap with an indefinite container size)
476
477### Removed
478
479- Removed `top_from_points`, `bot_from_points`, `top_from_percent`, and `bot_from_percent` methods removed from `Rect<Dimension>`. These functions were incredibly specific for an unusual use case, so we would be surprised if anyone was using them. Please use the new style helpers instead.
480- Removed `min_main_size`, `max_main_size`, `min_cross_size`, `max_cross_size`, and `cross_size` methods from `Style`. Use the more general `cross` and `main` methods directly on the `size`, `min_size`, and `max_size` properties instead.
481- Removed `main_margin_start`, `main_margin_end`, `cross_margin_start`, `cross_margin_end` from `Style`. Use the more general `main_start`, `main_end`, `cross_start`, and `cross_end` on the `margin` property instead.
482
483## 0.2.2
484
485### Fixes
486
487- Border or padding on the horizontal axis could, in some cases, increase the height of nodes.
488
489## 0.2.1
490
491### Fixes
492
493- In case of conflicts, `min_size` now overrides `max_size` which overrides `size` (#261). This is the behaviour specified in the CSS specification, and was also the behaviour in Taffy `v0.1.0`, but a regression was introduced in Taffy `v0.2.0`.
494- `taffy::compute_layout` has been made public allowing Taffy to be used with custom storage (#263)
495
496## 0.2.0
497
498### New features
499
500#### Flexbox "gap" and `AlignContent::SpaceEvenly`
501
502The [gap](https://developer.mozilla.org/en-US/docs/Web/CSS/gap) property is now supported on flex containers. This can make it much easier to create even spacing or "gutters" between nodes.
503
504Additionally we have a `SpaceEvenly` variant to the `AlignContent` enum to support evenly spaced justification in the cross axis (equivalent to  `align-content: space-evenly` in CSS)
505
506#### Debug module and cargo feature
507
508Two debugging features have been added:
509
510- `taffy::debug::print_tree(&Taffy, root)` - This will print a debug representation of the computed layout of an entire node tree (starting at `root`), which can be useful for debugging layouts.
511- A cargo feature `debug`. This enabled debug logging of the layout computation process itself (this is probably mainly useful for those working taffy itself).
512
513### Performance improvements
514
515A number of performance improvements have landed since taffy 0.1:
516
517- Firstly, our custom `taffy::forest` storage implementation was ripped out and replaced with a much simpler implementation using the `slotmap` crate. This led to performance increases of up to 90%.
518- Secondly, the caching implementation was improved by upping the number of cache slots from 2 to 4 and tweaking how computed results are allocated to chache slots to better match the actual usage patterns of the flexbox layout algorithm. This had a particularly dramatic effect on deep hierachies (which often involve recomputing the same results repeatedly), fixing the exponential blowup that was previously exhibited on these trees and improving performance by over 1000x in some cases!
519
520#### Benchmarks vs. Taffy 0.1
521
522| Benchmark                                 | Taffy 0.1 | Taffy 0.2 | % change (0.1 -> 0.2) |
523| ---                                       | ---       | ---       | ---                   |
524| wide/1_000 nodes (2-level hierarchy)      | 699.18 µs | 445.01 µs | -36.279%              |
525| wide/10_000 nodes (2-level hierarchy)     | 8.8244 ms | 7.1313 ms | -16.352%              |
526| wide/100_000 nodes (2-level hierarchy)    | 204.48 ms | 242.93 ms | +18.803%              |
527| deep/4000 nodes (12-level hierarchy))     | 5.2320 s  | 2.7363 ms | -99.947%              |
528| deep/10_000 nodes (14-level hierarchy)    | 75.207 s  | 6.9415 ms | -99.991%              |
529| deep/100_000 nodes (17-level hierarchy)   | -         | 102.72 ms | -                     |
530| deep/1_000_000 nodes (20-level hierarchy) | -         | 799.35 ms | -                     |
531
532(note that the table above contains multiple different units (milliseconds vs. microseconds vs. nanoseconds))
533
534As you can see, we have actually regressed slightly in the "wide" benchmarks (where all nodes are siblings of a single parent node). Although it should be noted our results in these benchmarks are still very fast, especially on the 10,000 node benchmark which we consider to be the most realistic size where the result is measured in microseconds.
535
536However, in the "deep" benchmarks we see dramatic improvements. The previous version of Taffy suffered from exponential blowup in the case of deeply nested hierachies. This has resulted in somewhat silly improvements like the 10,000 node (14-level) hierachy where Taffy 0.2 is a full 1 million times faster than Taffy 0.1. We've also included results with larger numbers of nodes (although you're unlikely to need that many) to demonstrate that this scalability continues up to even deeper levels of nesting.
537
538#### Benchmarks vs. [Yoga](https://github.com/facebook/yoga)
539
540Yoga benchmarks run via it's node.js bindings (the `yoga-layout-prebuilt` npm package), they were run a few times manually and it was verified that variance in the numbers of each run was minimal. It should be noted that this is using an old version of Yoga.
541
542| Benchmark | Yoga | Taffy 0.2 |
543| --- | --- | --- |
544| yoga/10 nodes (1-level hierarchy) | 45.1670 µs | 33.297 ns |
545| yoga/100 nodes (2-level hierarchy) | 134.1250 µs | 336.53 ns |
546| yoga/1_000 nodes (3-level hierarchy) | 1.2221 ms | 3.8928 µs |
547| yoga/10_000 nodes (4-level hierarchy) | 13.8672 ms | 36.162 µs |
548| yoga/100_000 nodes (5-level hierarchy) | 141.5307 ms | 1.6404 ms |
549
550(note that the table above contains multiple different units (milliseconds vs. microseconds vs. nanoseconds))
551
552While we're trying not to get too excited (there could easily be an issue with our benchmarking methodology which make this an unfair comparison), we are pleased to see that we seem to be anywhere between 100x and 1000x times faster depending on the node count!
553
554### Breaking API changes
555
556#### Node creation changes
557
558- `taffy::Node` is now unique only to the Taffy instance from which it was created.
559- Renamed `Taffy.new_node(..)` -> `Taffy.new_with_children(..)`
560- Renamed `Taffy.new_leaf()` -> `Taffy.new_leaf_with_measure()`
561- Added `taffy::node::Taffy.new_leaf()` which allows the creation of new leaf-nodes without having to supply a measure function
562
563#### Error handling/representation improvements
564
565- Renamed `taffy::Error` -> `taffy::error::TaffyError`
566- Replaced `taffy::error::InvalidChild` with a new `InvalidChild` variant of `taffy::error::TaffyError`
567- Replaced `taffy::error::InvalidNode` with a new `InvalidNode` variant of `taffy::error::TaffyError`
568- The following method new return `Err(TaffyError::ChildIndexOutOfBounds)` instead of panicking:
569  - `taffy::Taffy::remove_child_at_index`
570  - `taffy::Taffy::replace_child_at_index`
571  - `taffy::Taffy::child_at_index`
572- `Taffy::remove` now returns a `Result<usize, Error>`, to indicate if the operation was sucessful (and if it was, which ID was invalidated).
573
574#### Some uses of `Option<f32>` replaced with a new `AvailableSpace` enum
575
576A new enum `Taffy::layout::AvailableSpace` has been added.
577
578The definition looks like this:
579
580```rust
581/// The amount of space available to a node in a given axis
582pub enum AvailableSpace {
583    /// The amount of space available is the specified number of pixels
584    Definite(f32),
585    /// The amount of space available is indefinite and the node should be laid out under a min-content constraint
586    MinContent,
587    /// The amount of space available is indefinite and the node should be laid out under a max-content constraint
588    MaxContent,
589}
590```
591
592This enum is now used instead of `Option<f32>` when calling `Taffy.compute_layout` (if you previously passing `Size::NONE` to `compute_layout`, then you will need to change this to `Size::MAX_CONTENT`).
593
594And a different instance of it is passed as a new second parameter to `MeasureFunc`. `MeasureFunc`s may choose to use this parameter in their computation or ignore it as they see fit. The canonical example of when it makes sense to use it is when laying out text. If `MinContent` has been passed in the axis in which the text is flowing (i.e. the horizontal axis for left-to-right text), then you should line-break at every possible opportunity (e.g. all word boundaries), whereas if `MaxContent` has been passed then you shouldn't line break at all..
595
596#### Builder methods are now `const` where possible
597
598- Several convenience constants have been defined: notably `Style::DEFAULT`
599- `Size<f32>.zero()` is now `Size::<f32>::ZERO`
600- `Point<f32>.zero()` is now  `Point::<f32>::ZERO`
601- `Size::undefined()` is now `Size::NONE`
602
603#### Removals
604
605- Removed `taffy::forest::Forest`. `taffy::node::Taffy` now handles it's own storage using a slotmap (which comes with a performance boost up to 90%).
606- Removed `taffy::number::Number`. Use `Option<f32>` is used instead
607  - the associated public `MinMax` and `OrElse` traits have also been removed; these should never have been public
608- Removed unused dependencies `hashbrown`, `hash32`, and `typenum`. `slotmap` is now the only required dependency (`num_traits` and `arrayvec` are also required if you wish to use taffy in a `no_std` environment).
609
610### Fixes
611
612- Miscellaneous correctness fixes which align our implementation with Chrome:
613
614  - Nodes can only ever have one parent
615  - Fixed rounding of fractional values to follow latest Chrome - values are now rounded the same regardless of their position
616  - Fixed computing free space when using both `flex-grow` and a minimum size
617  - Padding is now only subtracted when determining the available space if the node size is unspecified, following [section 9.2.2 of the flexbox spec](https://www.w3.org/TR/css-flexbox-1/#line-sizing)
618  - `MeasureFunc` (and hence `NodeData` and hence `Forest` and hence the public `Taffy` type) are now `Send` and `Sync`, enabling their use in async and parallel applications
619- Taffy can now be vendored using `cargo-vendor` (README.md is now included in package).
620
621## 0.1.0
622
623### 0.1.0 Changed
624
625- the `order` field of `Layout` is now public, and describes the relative z-ordering of nodes
626- renamed crate from `stretch2` to `taffy`
627- updated to the latest version of all dependencies to reduce upstream pain caused by duplicate dependencies
628- renamed `stretch::node::Strech` -> `taffy::node::Taffy`
629
630### 0.1.0 Fixed
631
632- fixed feature strategy for `alloc` and `std`: these can now be compiled together, with `std`'s types taking priority
633
634### 0.1.0 Removed
635
636- removed Javascript / Kotlin / Swift bindings
637  - the maintainer team lacks expertise to keep these working
638  - more serious refactors are planned, and this will be challenging to keep working through that process
639  - if you are interested in helping us maintain bindings to other languages, [get in touch](https://github.com/DioxusLabs/taffy/discussions)!
640- the `serde_camel_case` and `serde_kebab_case` features have been removed: they were poorly motivated and were not correctly additive (if both were enabled compilation would fail)
641- removed the `Direction` and `Overflow` structs, and the corresponding `direction` and `overflow` fields from `Style`
642  - these had no effect in the current code base and were actively misleading
643
644## stretch2 0.4.3
645
646This is the final release of `stretch`: migrate to the crate named `taffy` for future fixes and features!
647
648These notes describe the differences between this release and `stretch` 0.3.2, the abandoned crate from which this library was forked.
649
650### Changed
651
652- updated [assorted dependencies](https://github.com/vislyhq/stretch/commit/a6491117379cea52dedc9584d892594a143e8cb0)
653
654### Fixed
655
656- fixed an exponential performance blow-up with deep nesting
657- fixed percent height values, which were using parent width
658- recomputing layout no longer moves children of non-zero-positioned parent
659- fixed broken Swift bindings