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