1# Release Notes
2
3## 0.2.1 (unreleased)
4
5### Fixes
6
7- `taffy::compute_layout` has been made public allowing Taffy to be used with custom storage (#263)
8
9- In case of conflicts, `min_size` now overrides `max_size` which overrides `size` (#261)
10
11## 0.2.0
12
13### New features
14
15#### Flexbox "gap" and `AlignContent::SpaceEvenly`
16
17The [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.
18
19Additionally 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)
20
21#### Debug module and cargo feature
22
23Two debugging features have been added:
24
25- `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.
26
27- A cargo feature `debug`. This enabled debug logging of the layout computation process itself (this is probably mainly useful for those working taffy itself).
28
29### Performance improvements
30
31A number of performance improvements have landed since taffy 0.1:
32
33- 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%.
34- Secondly, the caching implementation was improved by upping the number of cache slots from 2 to 4 and tweaking how computed results are allocated to chache slots to better match the actual usage patterns of the flexbox layout algorithm. This had a particularly dramatic effect on deep hierachies (which often involve recomputing the same results repeatedly), fixing the exponential blowup that was previously exhibited on these trees and improving performance by over 1000x in some cases!
35
36#### Benchmarks vs. Taffy 0.1
37
38| Benchmark | Taffy 0.1 | Taffy 0.2 | % change (0.1 -> 0.2) |
39| --- | --- | --- | --- |
40| wide/1_000 nodes (2-level hierarchy) | 3.5458 µs | 4.3571 µs | +23.333% |
41| wide/10_000 nodes (2-level hierarchy) | 36.418 µs | 42.967 µs | +17.357% |
42| wide/100_000 nodes (2-level hierarchy) | 1.8275 ms | 3.9096 ms | +112.26% |
43| deep/4000 nodes (12-level hierarchy)) | 5.1845 s | 15.318 µs | -100.000% |
44| deep/10_000 nodes (14-level hierarchy) | 75.978 s | 40.315 µs | -100.000% |
45| deep/100_000 nodes (17-level hierarchy) | - | 2.7644 ms| - |
46| deep/1_000_000 nodes (20-level hierarchy) | - | 1.2130 s| - |
47
48(note that the table above contains multiple different units (milliseconds vs. microseconds vs. nanoseconds))
49
50As 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.
51
52However, in the "deep" benchmarks we see dramatic improvements. The previous version of Taffy suffered from exponential blowup in the case of deeply nested hierachies. This has resulted in somewhat silly improvements like the 10,000 node (14-level) hierachy where Taffy 0.2 is a full 1 million times faster than Taffy 0.1. We've also included results with larger numbers of nodes (although you're unlikely to need that many) to demonstrate that this scalability continues up to even deeper levels of nesting.
53
54#### Benchmarks vs. [Yoga](https://github.com/facebook/yoga)
55
56Yoga 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.
57
58| Benchmark | Yoga | Taffy 0.2 |
59| --- | --- | --- |
60| yoga/10 nodes (1-level hierarchy) | 45.1670 µs | 33.297 ns |
61| yoga/100 nodes (2-level hierarchy) | 134.1250 µs | 336.53 ns |
62| yoga/1_000 nodes (3-level hierarchy) | 1.2221 ms | 3.8928 µs |
63| yoga/10_000 nodes (4-level hierarchy) | 13.8672 ms | 36.162 µs |
64| yoga/100_000 nodes (5-level hierarchy) | 141.5307 ms | 1.6404 ms |
65
66(note that the table above contains multiple different units (milliseconds vs. microseconds vs. nanoseconds))
67
68While 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!
69
70### Breaking API changes
71
72#### Node creation changes
73
74- `taffy::Node` is now unique only to the Taffy instance from which it was created.
75- Renamed `Taffy.new_node(..)` -> `Taffy.new_with_children(..)`
76- Renamed `Taffy.new_leaf()` -> `Taffy.new_leaf_with_measure()`
77- Added `taffy::node::Taffy.new_leaf()` which allows the creation of new leaf-nodes without having to supply a measure function
78
79#### Error handling/representation improvements
80
81- Renamed `taffy::Error` -> `taffy::error::TaffyError`
82- Replaced `taffy::error::InvalidChild` with a new `InvalidChild` variant of `taffy::error::TaffyError`
83- Replaced `taffy::error::InvalidNode` with a new `InvalidNode` variant of `taffy::error::TaffyError`
84- The following method new return `Err(TaffyError::ChildIndexOutOfBounds)` instead of panicking:
85  - `taffy::Taffy::remove_child_at_index`
86  - `taffy::Taffy::replace_child_at_index`
87  - `taffy::Taffy::child_at_index`
88- `Taffy::remove` now returns a `Result<usize, Error>`, to indicate if the operation was sucessful (and if it was, which ID was invalidated).
89
90#### Some uses of `Option<f32>` replaced with a new `AvailableSpace` enum
91
92A new enum `Taffy::layout::AvailableSpace` has been added.
93
94The definition looks like this:
95
96```rust
97/// The amount of space available to a node in a given axis
98pub enum AvailableSpace {
99    /// The amount of space available is the specified number of pixels
100    Definite(f32),
101    /// The amount of space available is indefinite and the node should be laid out under a min-content constraint
102    MinContent,
103    /// The amount of space available is indefinite and the node should be laid out under a max-content constraint
104    MaxContent,
105}
106```
107
108This 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`).
109
110And 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..
111
112#### Builder methods are now `const` where possible
113
114- Several convenience constants have been defined: notably `Style::DEFAULT`
115- `Size<f32>.zero()` is now `Size::<f32>::ZERO`
116- `Point<f32>.zero()` is now  `Point::<f32>::ZERO`
117- `Size::undefined()` is now `Size::NONE`
118
119#### Removals
120
121- 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%).
122- Removed `taffy::number::Number`. Use `Option<f32>` is used instead
123  - the associated public `MinMax` and `OrElse` traits have also been removed; these should never have been public
124- 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).
125
126### Fixes
127
128- Miscellaneous correctness fixes which align our implementation with Chrome:
129
130  - Nodes can only ever have one parent
131  - Fixed rounding of fractional values to follow latest Chrome - values are now rounded the same regardless of their position
132  - Fixed computing free space when using both `flex-grow` and a minimum size
133  - 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)
134  - `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
135- Taffy can now be vendored using `cargo-vendor` (README.md is now included in package).
136
137## 0.1.0
138
139### 0.1.0 Changed
140
141- the `order` field of `Layout` is now public, and describes the relative z-ordering of nodes
142- renamed crate from `stretch2` to `taffy`
143- updated to the latest version of all dependencies to reduce upstream pain caused by duplicate dependencies
144- renamed `stretch::node::Strech` -> `taffy::node::Taffy`
145
146### 0.1.0 Fixed
147
148- fixed feature strategy for `alloc` and `std`: these can now be compiled together, with `std`'s types taking priority
149
150### 0.1.0 Removed
151
152- removed Javascript / Kotlin / Swift bindings
153  - the maintainer team lacks expertise to keep these working
154  - more serious refactors are planned, and this will be challenging to keep working through that process
155  - if you are interested in helping us maintain bindings to other languages, [get in touch](https://github.com/DioxusLabs/taffy/discussions)!
156- 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)
157- removed the `Direction` and `Overflow` structs, and the corresponding `direction` and `overflow` fields from `Style`
158  - these had no effect in the current code base and were actively misleading
159
160## stretch2 0.4.3
161
162This is the final release of `stretch`: migrate to the crate named `taffy` for future fixes and features!
163
164These notes describe the differences between this release and `stretch` 0.3.2, the abandoned crate from which this library was forked.
165
166### Changed
167
168- updated [assorted dependencies](https://github.com/vislyhq/stretch/commit/a6491117379cea52dedc9584d892594a143e8cb0)
169
170### Fixed
171
172- fixed an exponential performance blow-up with deep nesting
173- fixed percent height values, which were using parent width
174- recomputing layout no longer moves children of non-zero-positioned parent
175- fixed broken Swift bindings