1# Release Notes
2
3## 0.5.0
4
5The changes in 0.5 are relatively small but the new measure function parameter is a breaking change so it requires a minor version bump.
6
7- Added: A `style: &Style` parameter has been added to measure functions.
8- Added: The `MaybeMath`, `MaybeResolve`, and `ResolveOrZero` traits have been made public.
9- Fix: use SizingMode::Inherent when sizing absolute children of flexbox nodes.
10
11## 0.4.4
12
13### Fixes
14
15- Content alignment (`align-content`/`justify-content`) behaviour was updated to match the latest spec (and Chrome 123+) (#635)
16- Ensure that root Flexbox nodes are floored by their padding-border (#651, #655)
17- Use grid area size not available space when applying aspect ratio to grid containers (#656)
18
19## 0.4.3
20
21### Fixes
22
23- Fix compilation error in `evenly_sized_tracks` style helper in recent versions of rustc caused by a change/regression in type
24  inference (#643). Note that 3rd-party code that call style helpers that take an `Into<f32>` parameter may still be affected by this issue,
25  but they should be able to fix on their side by clarifying the type passed in
26
27## 0.4.2
28
29- Fixed: single-line flex-container should clamp the line's cross-size (#638)
30- Reduced binary footprint of Taffy from around 300kb to around 150kb (#636)
31
32## 0.4.1
33
34- Fixed: CSS Grid track sizing not respecting growth limits in some circumstances (#624)
35
36## 0.4.0
37
38### Highlights
39
40- Support for CSS Block layout (`display: block`)
41- Support for the `overflow` property (+ `scrollbar_width` for `overflow: scroll`)
42- Improved measure function API
43- Completely refactored low-level API
44- Simplified module hierarchy (+ most types/functions are now exported from the crate root)
45- Expanded set of examples which better document integration with other layout systems (e.g. text layout)
46- Computed values for `padding` and `border` are now output into the `Layout` struct
47
48### Block layout
49
50Support 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  full flow layout: inline, inline-block and float layout have *not* been implemented. The use case supported is block container nodes which contain block-level children.
51
52### Overflow property
53
54Support has been added for a new `overflow` style property with `Visible`, `Clip`, `Hidden`, and `Scroll` values (`Auto` is not currently implemented). Additionally a `scrollbar_width` property has been added to control the size of scrollbars for nodes with `Overflow::Scroll` set.
55
56- Overflow is settable indpendently in each axis.
57- `Visible` and `Clip` will produce layouts equivalent to the Taffy 0.3. `Clip` will affect the new `content_size` output by restricting it to the available space.
58- `Hidden` and `Scroll` affect layout by changing the automatic minimum size of Flexbox and Grid children
59- `Scroll` additionally reserves `scrollbar_width` pixels for a scrollbar in the opposite axis to which scrolling is enabled. `Scroll` with `scrollbar_width` set to zero is equivalent to `Hidden`.
60
61### Measure function changes
62
63The "measure function" API for integrating Taffy with other measurement systems (such as text layout) has been changed to be more flexible
64and to interact better with borrow checking (you can now borrow external data in your measure function!).
65
66- There are no longer per-node measure functions.
67- There is now a single "global" measure function, and a per-node "context" of a user-defined type
68- The `Taffy` tree is now a generic `TaffyTree<T>` where `T` is the "context" type.
69- The measure function is now called for all leaf nodes (nodes without children). If you wish to maintain compatibility with the previous
70  behaviour then your measure function should return `Size::ZERO` for leaf nodes whose context is `None`.
71
72If you are not using measure functions, then the only change you will need to make is from:
73
74```rust
75let mut tree = Taffy::new();
76```
77
78to
79
80```rust
81let mut tree : TaffyTree<()> = TaffyTree::new();
82```
83
84And generally update any uses of `Taffy` in your codebase to `TaffyTree<()>`.
85
86If you are using measure functions then you will need to make some bigger (but straightforward) changes. The following Taffy 0.3 code:
87
88```rust
89let mut tree = Taffy::new();
90let leaf = tree.new_leaf_with_measure(
91  Style::DEFAULT,
92  |known_dimensions: Size<Option<f32>>, available_space: Size<AvailableSpace>| Size { width: 100.0, height: 200.0 }
93);
94tree.compute_layout(leaf, Size::MAX_CONTENT);
95```
96
97Should become something like the following with Taffy 0.4:
98
99```rust
100let mut tree : TaffyTree<Size> = TaffyTree::new();
101let leaf = tree.new_leaf_with_context(Style::DEFAULT, Size { width: 100.0, height: 200.0 });
102tree.compute_layout_with_measure(
103  leaf,
104  Size::MAX_CONTENT,
105  |known_dimensions: Size<Option<f32>>, available_space: Size<AvailableSpace>, node_id: NodeId, node_context: Option<Size>| {
106    node_context.unwrap_or(Size::ZERO)
107  }
108);
109```
110
111Note that:
112
113- 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).
114- If you don't need a context then you can use `()` for the context type
115- As the single "global" measure function passed to `compute_layout_with_measure` only needs to exist for the duration of a single layout run,
116  it can (mutably) borrow data from it's environment
117
118### Low-level API (`LayoutTree` trait) refactor
119
120The low-level API has been completely reworked:
121
122- The `LayoutTree` trait has been split into 5 smaller traits which live in the `taffy::tree:traits` module (along with their associated documentation)
123- The following methods have been removed from split `LayoutTree` traits entirely: `parent`, `is_childless`, `measure_node`, `needs_measure`, and `mark_dirty`.
124- `taffy::node::Node` has been replaced with `taffy::NodeId`. This should make it much easier to implement the low-level traits as the underlying type backing the node id now a `u64` rather than a `slotmap::DefaultKey`.
125- Support for running each layout algorithm individually on a single node via the following top-level functions:
126  - `compute_flexbox_layout`
127  - `compute_grid_layout`
128  - `compute_block_layout`
129  - `compute_leaf_layout`
130  - `compute_root_layout`
131  - `compute_hidden_layout`
132
133It is believed that nobody was previously using the low-level API so we are not providing a migration guide. However, along with the refactor we have greatly
134improved both the documentation and have added examples using the new API, both of which are linked to from the [main documentation page](https://docs.rs/taffy).
135
136### Module hierarchy changes
137
138The specific changes are detailed below. However for most users the most significant change will be that almost all types are now re-exported from the root module. This means that module specific imports like `use taffy::layout::Layout` can now in almost all cases be replaced with the simpler `use taffy::Layout`.
139
140Specific changes:
141
142- The `math` module has been made private
143- The `axis` module has been merged into the `geometry` module
144- The debug module is no longer public. The `print_tree` function is now accessible under `util`.
145- All types from the `node`, `data`, `layout`, `error` and `cache` modules have been moved to the  the `tree` module.
146- The `layout_flexbox()` function has been removed from the prelude. Use `taffy::compute_flexbox_layout` instead.
147
148### Many APIs have been renamed to replace `points` or `Points` with `length` or `Length`
149
150This new name better describes one-dimensional measure of space in some unspecified unit
151which is often unrelated to the PostScript point or the CSS `pt` unit.
152
153This also removes a misleading similarity with the 2D `Point`,
154whose components can have any unit and are not even necessarily absolute lengths.
155
156Example usage change:
157
158```diff
159 use taffy::prelude::*;
160
161 // …
162
163 let header_node = taffy
164     .new_leaf(
165         Style {
166-            size: Size { width: points(800.0), height: points(100.0) },
167+            size: Size { width: length(800.0), height: length(100.0) },
168             ..Default::default()
169         },
170     ).unwrap();
171```
172
173### Other Changes
174
175- The `Taffy` type was renamed to `TaffyTree` and made generic of a context parameter
176- The Flexbox algorithm has now been moved behind the `flexbox` feature. The `flexbox` feature is enabled by default.
177- The `justify_self` property has been moved behind the `grid` feature.
178- Fixed misspelling: `RunMode::PeformLayout` renamed into `RunMode::PerformLayout` (added missing `r`).
179- `serde` dependency has been made compatible with `no_std` environments
180- `slotmap` dependency has been made compatible with `no_std` environments
181- Added `insert_child_at_index()` method to the `TaffyTree`. This can be used to insert a child node at any position instead of just the end.
182- Added `total_node_count()` method to the `TaffyTree` which returns the total number of nodes in the tree.
183- Added `get_disjoint_node_context_mut()` method to the `TaffyTree`. This can be used to safely get multiple mutable borrows at the same time.
184
185## 0.3.19
186
187### Fixes
188
189- Fix compilation error in `evenly_sized_tracks` style helper in recent versions of rustc caused by a change/regression in type
190  inference (#643). Note that 3rd-party code that call style helpers that take an `Into<f32>` parameter may still be affected by this issue,
191  but they should be able to fix on their side by clarifying the type passed in
192
193## 0.3.18
194
195### Fixes
196
197- Fix computation of Flexbox automatic minimum size when grid or flexbox child has an explicit width/height style set (#576)
198
199## 0.3.17
200
201### Added
202
203- Added `total_node_count` method to the `Taffy` struct. Returns the total number of nodes in the tree.
204
205## 0.3.16
206
207### Fixes
208
209- Improve performance of flexbox columns
210
211## 0.3.15
212
213### Fixes
214
215- Fix justify-content and align-content when free space is negative (content overflows container) (#549) (#551)
216
217## 0.3.14
218
219### Fixes
220
221- 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)
222
223## 0.3.13
224
225### Fixes
226
227- Fix rounding accumulation bug (#521) (Fixes #501 and bevyengine/bevy#8911)
228- Flexbox: pass correct cross-axis available space when computing an item's intrinsic main size (#522)(Fixes bevyengine/bevy#9350)
229- Flexbox: Subtract child margin not parent margin when computing stretch-alignment known size
230- Grid: Make CSS Grid algorithm correctly apply max width/height and available space when it is the root node (#491)
231- Grid: Fix CSS Grid "auto track" / placement bugs #481
232  - Fix divide by zero when using grid_auto_rows/grid_auto_columns with zero negative implicit tracks
233  - Fix over counting of tracks (leading to incorrect container heights) when auto-placing in grids that contain negative implicit tracks.
234  - Fix axis conflation in auto-placement code when grid_auto_flow is column
235  - Fix assignment of auto track sizes when initializing negative implicit tracks
236- Leaf: Apply margins to leaf nodes when computing available space for measure functions
237- Leaf: Reserve space for padding/borders in nodes with measure functions (#497)
238  
239  **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.
240
241### Dependencies
242
243- Upgrade `grid` to `0.10`. This eliminates the transitive dependency on `no-std-compat`.
244
245## 0.3.12
246
247### Fixes
248
249- Fix caching issue when toggling `display:none` on and off
250
251## 0.3.11
252
253### Fixes
254
255- Fix exponential blowup when laying out trees containing nodes with min and max sizes.
256
257## 0.3.10
258
259### Fixes
260
261- Fix sizing of children when the available_space < min_size (#407)
262
263## 0.3.9
264
265### Fixes
266
267- 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)
268
269## 0.3.8
270
271### Fixes
272
273- Fix incorrect min-content size for `flex-wrap: wrap` nodes (bevyengine/bevy#8082)
274
275## 0.3.7
276
277### Fixes
278
279- Fix: Make `padding` and `border` floor node sizes (#372)
280- Fix: Prevent percentages contributing to min-content sizes (#388) (also fixes bevyengine/bevy#8017)
281
282## 0.3.6
283
284### Fixes
285
286- Fix: Ignore `align_content` when `flex_wrap` is set to `nowrap` (#383)
287
288## 0.3.5
289
290### Fixes
291
292- Fix `display: none` when it is set on a flexbox child (#380)
293- Fix `display: none` when it is set on a grid child (#381)
294
295## 0.3.4
296
297### Fixes
298
299- Fix `display: none` when it is set for the only node in the hierarchy (#377)
300
301## 0.3.3
302
303### Added
304
305- 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.
306
307### Fixes
308
309- Fixed rounding algorithm such that it never leaves gaps between adjacent nodes (#369)
310- Fixed compiling with the `grid` feature disabled (#370)
311- Fixed compiling with the `std` feature disabled
312
313## 0.3.2
314
315### Fixes
316
317- Allow partial nested values to be deserialized into a `Style` using the `serde` feature.
318
319## 0.3.1
320
321### Fixes
322
323- The `serde` feature now works when the `grid` feature is enabled
324
325## 0.3.0
326
327### Highlights
328
329- [CSS Grid algorithm support](#new-feature-css-grid)
330- [Style helper functions](#new-feature-style-helpers)
331
332See below for details of breaking changes.
333
334### New Feature: CSS Grid
335
336We 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`.
337
338#### Learning Resources
339
340Taffy 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:
341
342- [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.
343- [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 comprehensive written explanation of the different Grid properties and how they work.
344
345#### Supported Features & Properties
346
347In addition to the usual sizing/spacing properties (size, min_size, padding, margin, etc), the following Grid style properties are supported on Grid Containers:
348
349| Property                  | Explanation                                                                                    |
350| ---                       | ---                                                                                            |
351| [`grid-template-columns`] | The track sizing functions of the grid's explicit columns                                      |
352| [`grid-template-rows`]    | The track sizing functions of the grid's explicit rows                                         |
353| [`grid-auto-rows`]        | Track sizing functions for the grid's implicitly generated rows                                |
354| [`grid-auto-columns`]     | Track sizing functions for the grid's implicitly generated columns                             |
355| [`grid-auto-flow`]        | Whether auto-placed items are placed row-wise or column-wise. And sparsely or densely.         |
356| [`gap`]                   | The size of the vertical and horizontal gaps between grid rows/columns                         |
357| [`align-content`]         | Align grid tracks within the container in the inline (horizontal) axis                         |
358| [`justify-content`]       | Align grid tracks within the container in the block (vertical) axis                            |
359| [`align-items`]           | Align the child items within their grid areas in the inline (horizontal) axis                  |
360| [`justify-items`]         | Align the child items within their grid areas in the block (vertical) axis                     |
361
362And the following Grid style properties are supported on Grid Items (children):
363
364| Property                  | Explanation                                                                                    |
365| ---                       | ---                                                                                            |
366| [`grid-row`]              | The (row) grid line the item starts at (or a span)                                             |
367| [`grid-column`]           | The (column) grid line the item end at (or a span)                                             |
368| [`align-self`]            | Align the item within it's grid area in the inline (horizontal) axis. Overrides `align-items`. |
369| [`justify-self`]          | Align the item within it's grid area in the block (vertical) axis. Overrides `justify-items`.  |
370
371[`grid-template-columns`]: https://developer.mozilla.org/en-US/docs/Web/CSS/grid-template-columns
372[`grid-template-rows`]: https://developer.mozilla.org/en-US/docs/Web/CSS/grid-template-rows
373[`grid-auto-rows`]: https://developer.mozilla.org/en-US/docs/Web/CSS/grid-auto-rows
374[`grid-auto-columns`]: https://developer.mozilla.org/en-US/docs/Web/CSS/grid-auto-columns
375[`grid-auto-flow`]: https://developer.mozilla.org/en-US/docs/Web/CSS/grid-auto-flow
376[`gap`]: https://developer.mozilla.org/en-US/docs/Web/CSS/gap
377[`align-content`]: https://developer.mozilla.org/en-US/docs/Web/CSS/align_content
378[`justify-content`]: https://developer.mozilla.org/en-US/docs/Web/CSS/justify_content
379[`align-items`]: https://developer.mozilla.org/en-US/docs/Web/CSS/align-items
380[`justify-items`]: https://developer.mozilla.org/en-US/docs/Web/CSS/justify-items
381[`grid-row`]: https://developer.mozilla.org/en-US/docs/Web/CSS/grid-row
382[`grid-column`]: https://developer.mozilla.org/en-US/docs/Web/CSS/grid-column
383[`align-self`]: https://developer.mozilla.org/en-US/docs/Web/CSS/align-self
384[`justify-self`]: https://developer.mozilla.org/en-US/docs/Web/CSS/justify-self
385
386The following properties and features are not currently supported:
387
388- Subgrids
389- Masonry grid layout
390- Named grid lines
391- Named areas: `grid-template-areas` and `grid-area`
392- `grid-template` or `grid` shorthand
393
394#### Example
395
396See [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:
397
398```bash
399cargo run --example grid_holy_grail --features grid
400```
401
402### New Feature: Style Helpers
403
404Ten 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.
405
406For example, instead of:
407
408```rust
409let size : Size<Dimension> = Size { width: Dimension::Points(100.0), height: Dimension::Percent(50.0) };
410```
411
412you can now write
413
414```rust
415let size : Size<Dimension> = Size { width: points(100.0), height: percent(50.0) };
416```
417
418And 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
419
420```rust
421let size : Size<Dimension> = points(100.0);
422```
423
424Available style helpers:
425
426<table>
427  <thead><tr><th>Type(s)</th><th colspan="2">Helpers that work with that type</th></tr></thead>
428  <tbody>
429    <tr>
430      <td rowspan="3"><code>LengthPercentage</code></td>
431      <td><code>zero()</code></td>
432      <td>Generates a <code>Points</code> variant with the value <code>0.0</code></td>
433    </tr>
434    <tr>
435      <td><code>points(val:&nbsp;f32)</code></td>
436      <td>Generates a <code>Points</code> variant with the specified value</td>
437    </tr>
438    <tr>
439      <td><code>percent(val:&nbsp;f32)</code></td>
440      <td>Generates a <code>Percent</code> variant with the specified value.<br />Note that the scale of 0-1 not 0-100.</td>
441    </tr>
442    <tr>
443      <td rowspan="2"><code>LengthPercentageAuto</code><br /><code>Dimension</code></td>
444      <td colspan="2"><i>All helpers from <code>LengthPercentage</code> and...</i></td>
445    </tr>
446    <tr>
447      <td><code>auto()</code></td>
448      <td>Generates an <code>Auto</code> variant</td>
449    </tr>
450    <tr>
451      <td rowspan="3"><code>MinTrackSizingFunction</code></td>
452      <td colspan="2"><i>All helpers from <code>LengthPercentageAuto</code>/<code>Dimension</code> and...</i></td>
453    </tr>
454    <tr>
455      <td><code>min_content()</code></td>
456      <td>Generates an <code>MinContent</code> variant</td>
457    </tr>
458      <tr>
459      <td><code>max_content()</code></td>
460      <td>Generates an <code>MinContent</code> variant</td>
461    </tr>
462    <tr>
463      <td rowspan="3"><code>MaxTrackSizingFunction</code></td>
464      <td colspan="2"><i>All helpers from <code>MinTrackSizingFunction</code> and...</i></td>
465    </tr>
466    <tr>
467      <td><code>fit_content(limit:&nbsp;LengthPercentage)</code></td>
468      <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>
469    </tr>
470      <tr>
471      <td><code>fr(fraction:&nbsp;f32)</code></td>
472      <td>Generates a <code>Fraction</code> (<code>fr</code>) variant with the specified flex fraction </td>
473    </tr>
474    <tr>
475      <td rowspan="3"><code>NonRepeatingTrackSizingFunction</code></td>
476      <td colspan="2"><i>All helpers from <code>MaxTrackSizingFunction</code> and...</i></td>
477    </tr>
478    <tr>
479      <td><code>minmax(min: MinTrackSizingFunction, max: MaxTrackSizingFunction)</code></td>
480      <td>Equivalent to CSS <code>minmax()</code> function.</td>
481    </tr>
482    <tr>
483      <td><code>flex(fraction:&nbsp;f32)</code></td>
484      <td>Equivalent to CSS <code>minmax(0px, 1fr)</code>. This is likely what you want if you want evenly sized rows/columns.</td>
485    </tr>
486    <tr>
487      <td rowspan="2"><code>TrackSizingFunction</code></td>
488      <td colspan="2"><i>All helpers from <code>NonRepeatingTrackSizingFunction</code> and...</i></td>
489    </tr>
490    <tr>
491      <td><code>repeat(rep: GridTrackRepetition, tracks: Vec&lt;TrackSizingFunction&gt;)</code></td>
492      <td>Equivalent to css <code>repeat()</code> function.</td>
493    </tr>
494    <tr>
495      <td><code>Vec&lt;TrackSizingFunction&gt;</code></td>
496      <td><code>evenly_sized_tracks(count:&nbsp;u16)</code></td>
497      <td>Equivalent to CSS <code>repeat(count, minmax(0px, 1fr)</code></td>
498    </tr>
499    <tr>
500      <td rowspan="3"><code>AvailableSpace</code></td>
501      <td><code>auto()</code></td>
502      <td>Generates an <code>Auto</code> variant</td>
503    </tr>
504    <tr>
505      <td><code>min_content()</code></td>
506      <td>Generates an <code>MinContent</code> variant</td>
507    </tr>
508      <tr>
509      <td><code>max_content()</code></td>
510      <td>Generates an <code>MinContent</code> variant</td>
511    </tr>
512    <tr>
513      <td><code>Size&lt;T&gt;</code></td>
514      <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>
515    </tr>
516    <tr>
517      <td><code>Rect&lt;T&gt;</code></td>
518      <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>
519    </tr>
520  </tbody>
521</table>
522
523### Breaking API changes
524
525#### Changes to alignment style types
526
527- `AlignContent` and `JustifyContent` has been merged.
528  - `JustifyContent` is now an alias of `AlignContent` and contains the `Stretch` variant.
529  - This variant will be *ignored* (falling back to `Start`) when applied Flexbox containers. It is valid value for Grid containers.
530- `AlignItems` and `AlignSelf` have been merged.
531  - The `Auto` variant of `AlignSelf` has been removed. You should now use `Option::None` if you wish to specify `AlignSelf::Auto`.
532  - `AlignSelf` is now an alias of `AlignItems`.
533  - `JustifyItems` and `JustifySelf` aliases have been added. These properties have no affect on Flexbox containers, but apply to Grid containers.
534- `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.
535
536#### Strict style types
537
538- New types `LengthPercentage` and `LengthPercentageAuto` have been added.
539  - `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.
540  - `LengthPercentageAuto` is currently identical to `Dimension` but will allow us to expand dimension in future to support values like `MinContent`, `MaxContent` and `FitContent`.
541- 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).
542
543#### Position properties renamed
544
545- 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)
546- 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`.
547
548#### Changes to `LayoutTree`
549
550- Added generic associated type to `LayoutTree` for a `ChildIter`, an iterator on the children of a given node.
551- 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.
552- 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.
553- Added `is_childless` method to `LayoutTree` for querying whether a node has no children.
554
555#### `AvailableSpace` has been moved
556
557The `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.
558
559### Fixes
560
561- Flexbox nodes sized under a min-content constraint now size correctly (#291)
562- Aspect ratio is now applied correctly in many circumstances
563- Absolutely positioned items now apply margins correctly
564- Min/max size are now applied correctly
565- Inset applied incorrectly to relatively positioned flexbox children when both `top` and `bottom` or `left` and `right` were specified (#348)
566- 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)
567
568### Removed
569
570- 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.
571- 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.
572- 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.
573
574## 0.2.2
575
576### Fixes
577
578- Border or padding on the horizontal axis could, in some cases, increase the height of nodes.
579
580## 0.2.1
581
582### Fixes
583
584- 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`.
585- `taffy::compute_layout` has been made public allowing Taffy to be used with custom storage (#263)
586
587## 0.2.0
588
589### New features
590
591#### Flexbox "gap" and `AlignContent::SpaceEvenly`
592
593The [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.
594
595Additionally 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)
596
597#### Debug module and cargo feature
598
599Two debugging features have been added:
600
601- `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.
602- A cargo feature `debug`. This enabled debug logging of the layout computation process itself (this is probably mainly useful for those working taffy itself).
603
604### Performance improvements
605
606A number of performance improvements have landed since taffy 0.1:
607
608- 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%.
609- 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 cache slots to better match the actual usage patterns of the flexbox layout algorithm. This had a particularly dramatic effect on deep hierarchies (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!
610
611#### Benchmarks vs. Taffy 0.1
612
613| Benchmark                                 | Taffy 0.1 | Taffy 0.2 | % change (0.1 -> 0.2) |
614| ---                                       | ---       | ---       | ---                   |
615| wide/1_000 nodes (2-level hierarchy)      | 699.18 µs | 445.01 µs | -36.279%              |
616| wide/10_000 nodes (2-level hierarchy)     | 8.8244 ms | 7.1313 ms | -16.352%              |
617| wide/100_000 nodes (2-level hierarchy)    | 204.48 ms | 242.93 ms | +18.803%              |
618| deep/4000 nodes (12-level hierarchy))     | 5.2320 s  | 2.7363 ms | -99.947%              |
619| deep/10_000 nodes (14-level hierarchy)    | 75.207 s  | 6.9415 ms | -99.991%              |
620| deep/100_000 nodes (17-level hierarchy)   | -         | 102.72 ms | -                     |
621| deep/1_000_000 nodes (20-level hierarchy) | -         | 799.35 ms | -                     |
622
623(note that the table above contains multiple different units (milliseconds vs. microseconds vs. nanoseconds))
624
625As 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.
626
627However, in the "deep" benchmarks we see dramatic improvements. The previous version of Taffy suffered from exponential blowup in the case of deeply nested hierarchies. This has resulted in somewhat silly improvements like the 10,000 node (14-level) hierarchy 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.
628
629#### Benchmarks vs. [Yoga](https://github.com/facebook/yoga)
630
631Yoga 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.
632
633| Benchmark | Yoga | Taffy 0.2 |
634| --- | --- | --- |
635| yoga/10 nodes (1-level hierarchy) | 45.1670 µs | 33.297 ns |
636| yoga/100 nodes (2-level hierarchy) | 134.1250 µs | 336.53 ns |
637| yoga/1_000 nodes (3-level hierarchy) | 1.2221 ms | 3.8928 µs |
638| yoga/10_000 nodes (4-level hierarchy) | 13.8672 ms | 36.162 µs |
639| yoga/100_000 nodes (5-level hierarchy) | 141.5307 ms | 1.6404 ms |
640
641(note that the table above contains multiple different units (milliseconds vs. microseconds vs. nanoseconds))
642
643While 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!
644
645### Breaking API changes
646
647#### Node creation changes
648
649- `taffy::Node` is now unique only to the Taffy instance from which it was created.
650- Renamed `Taffy.new_node(..)` -> `Taffy.new_with_children(..)`
651- Renamed `Taffy.new_leaf()` -> `Taffy.new_leaf_with_measure()`
652- Added `taffy::node::Taffy.new_leaf()` which allows the creation of new leaf-nodes without having to supply a measure function
653
654#### Error handling/representation improvements
655
656- Renamed `taffy::Error` -> `taffy::error::TaffyError`
657- Replaced `taffy::error::InvalidChild` with a new `InvalidChild` variant of `taffy::error::TaffyError`
658- Replaced `taffy::error::InvalidNode` with a new `InvalidNode` variant of `taffy::error::TaffyError`
659- The following method new return `Err(TaffyError::ChildIndexOutOfBounds)` instead of panicking:
660  - `taffy::Taffy::remove_child_at_index`
661  - `taffy::Taffy::replace_child_at_index`
662  - `taffy::Taffy::child_at_index`
663- `Taffy::remove` now returns a `Result<usize, Error>`, to indicate if the operation was successful (and if it was, which ID was invalidated).
664
665#### Some uses of `Option<f32>` replaced with a new `AvailableSpace` enum
666
667A new enum `Taffy::layout::AvailableSpace` has been added.
668
669The definition looks like this:
670
671```rust
672/// The amount of space available to a node in a given axis
673pub enum AvailableSpace {
674    /// The amount of space available is the specified number of pixels
675    Definite(f32),
676    /// The amount of space available is indefinite and the node should be laid out under a min-content constraint
677    MinContent,
678    /// The amount of space available is indefinite and the node should be laid out under a max-content constraint
679    MaxContent,
680}
681```
682
683This 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`).
684
685And 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..
686
687#### Builder methods are now `const` where possible
688
689- Several convenience constants have been defined: notably `Style::DEFAULT`
690- `Size<f32>.zero()` is now `Size::<f32>::ZERO`
691- `Point<f32>.zero()` is now  `Point::<f32>::ZERO`
692- `Size::undefined()` is now `Size::NONE`
693
694#### Removals
695
696- 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%).
697- Removed `taffy::number::Number`. Use `Option<f32>` is used instead
698  - the associated public `MinMax` and `OrElse` traits have also been removed; these should never have been public
699- 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).
700
701### Fixes
702
703- Miscellaneous correctness fixes which align our implementation with Chrome:
704
705  - Nodes can only ever have one parent
706  - Fixed rounding of fractional values to follow latest Chrome - values are now rounded the same regardless of their position
707  - Fixed computing free space when using both `flex-grow` and a minimum size
708  - 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)
709  - `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
710- Taffy can now be vendored using `cargo-vendor` (README.md is now included in package).
711
712## 0.1.0
713
714### 0.1.0 Changed
715
716- the `order` field of `Layout` is now public, and describes the relative z-ordering of nodes
717- renamed crate from `stretch2` to `taffy`
718- updated to the latest version of all dependencies to reduce upstream pain caused by duplicate dependencies
719- renamed `stretch::node::Stretch` -> `taffy::node::Taffy`
720
721### 0.1.0 Fixed
722
723- fixed feature strategy for `alloc` and `std`: these can now be compiled together, with `std`'s types taking priority
724
725### 0.1.0 Removed
726
727- removed Javascript / Kotlin / Swift bindings
728  - the maintainer team lacks expertise to keep these working
729  - more serious refactors are planned, and this will be challenging to keep working through that process
730  - if you are interested in helping us maintain bindings to other languages, [get in touch](https://github.com/DioxusLabs/taffy/discussions)!
731- 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)
732- removed the `Direction` and `Overflow` structs, and the corresponding `direction` and `overflow` fields from `Style`
733  - these had no effect in the current code base and were actively misleading
734
735## stretch2 0.4.3
736
737This is the final release of `stretch`: migrate to the crate named `taffy` for future fixes and features!
738
739These notes describe the differences between this release and `stretch` 0.3.2, the abandoned crate from which this library was forked.
740
741### Changed
742
743- updated [assorted dependencies](https://github.com/vislyhq/stretch/commit/a6491117379cea52dedc9584d892594a143e8cb0)
744
745### Fixed
746
747- fixed an exponential performance blow-up with deep nesting
748- fixed percent height values, which were using parent width
749- recomputing layout no longer moves children of non-zero-positioned parent
750- fixed broken Swift bindings