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