104 lines
4.7 KiB
Markdown
104 lines
4.7 KiB
Markdown
This crate provides [splines](https://en.wikipedia.org/wiki/Spline_(mathematics)), mathematic curves
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defined piecewise through control keys a.k.a. knots.
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Feel free to dig in the [online documentation](https://docs.rs/splines) for further information.
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<!-- cargo-sync-readme start -->
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# Spline interpolation made easy.
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This crate exposes splines for which each sections can be interpolated independently of each
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other – i.e. it’s possible to interpolate with a linear interpolator on one section and then
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switch to a cubic Hermite interpolator for the next section.
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Most of the crate consists of three types:
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- [`Key`], which represents the control points by which the spline must pass.
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- [`Interpolation`], the type of possible interpolation for each segment.
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- [`Spline`], a spline from which you can *sample* points by interpolation.
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When adding control points, you add new sections. Two control points define a section – i.e.
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it’s not possible to define a spline without at least two control points. Every time you add a
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new control point, a new section is created. Each section is assigned an interpolation mode that
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is picked from its lower control point.
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# Quickly create splines
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```
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use splines::{Interpolation, Key, Spline};
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let start = Key::new(0., 0., Interpolation::Linear);
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let end = Key::new(1., 10., Interpolation::default());
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let spline = Spline::from_vec(vec![start, end]);
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```
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You will notice that we used `Interpolation::Linear` for the first key. The first key `start`’s
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interpolation will be used for the whole segment defined by those two keys. The `end`’s
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interpolation won’t be used. You can in theory use any [`Interpolation`] you want for the last
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key. We use the default one because we don’t care.
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# Interpolate values
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The whole purpose of splines is to interpolate discrete values to yield continuous ones. This is
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usually done with the `Spline::sample` method. This method expects the interpolation parameter
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(often, this will be the time of your simulation) as argument and will yield an interpolated
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value.
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If you try to sample in out-of-bounds interpolation parameter, you’ll get no value.
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```
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# use splines::{Interpolation, Key, Spline};
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# let start = Key::new(0., 0., Interpolation::Linear);
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# let end = Key::new(1., 10., Interpolation::Linear);
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# let spline = Spline::from_vec(vec![start, end]);
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assert_eq!(spline.sample(0.), Some(0.));
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assert_eq!(spline.clamped_sample(1.), Some(10.));
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assert_eq!(spline.sample(1.1), None);
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```
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It’s possible that you want to get a value even if you’re out-of-bounds. This is especially
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important for simulations / animations. Feel free to use the `Spline::clamped_interpolation` for
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that purpose.
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```
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# use splines::{Interpolation, Key, Spline};
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# let start = Key::new(0., 0., Interpolation::Linear);
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# let end = Key::new(1., 10., Interpolation::Linear);
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# let spline = Spline::from_vec(vec![start, end]);
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assert_eq!(spline.clamped_sample(-0.9), Some(0.)); // clamped to the first key
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assert_eq!(spline.clamped_sample(1.1), Some(10.)); // clamped to the last key
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```
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# Features and customization
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This crate was written with features baked in and hidden behind feature-gates. The idea is that
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the default configuration (i.e. you just add `"splines = …"` to your `Cargo.toml`) will always
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give you the minimal, core and raw concepts of what splines, keys / knots and interpolation
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modes are. However, you might want more. Instead of letting other people do the extra work to
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add implementations for very famous and useful traits – and do it in less efficient way, because
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they wouldn’t have access to the internals of this crate, it’s possible to enable features in an
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ad hoc way.
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This mechanism is not final and this is currently an experiment to see how people like it or
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not. It’s especially important to see how it copes with the documentation.
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So here’s a list of currently supported features and how to enable them:
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- **Serialization / deserialization.**
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+ This feature implements both the `Serialize` and `Deserialize` traits from `serde` for all
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types exported by this crate.
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+ Enable with the `"serialization"` feature.
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- **[cgmath](https://crates.io/crates/cgmath) implementors.**
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+ Adds some useful implementations of `Interpolate` for some cgmath types.
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+ Enable with the `"impl-cgmath"` feature.
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- **[nalgebra](https://crates.io/crates/nalgebra) implementors.**
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+ Adds some useful implementations of `Interpolate` for some nalgebra types.
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+ Enable with the `"impl-nalgebra"` feature.
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- **Standard library / no standard library.**
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+ It’s possible to compile against the standard library or go on your own without it.
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+ Compiling with the standard library is enabled by default.
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+ Use `default-features = []` in your `Cargo.toml` to disable.
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+ Enable explicitly with the `"std"` feature.
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<!-- cargo-sync-readme end -->
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