Getting started

The Curves library finds points on smooth Bezier Curves and Splines. Give it a few points, and it tells you where the curve goes between them. Use it for easing animations, drawing paths, moving things along a route, or anything else that should bend smoothly instead of jumping in straight lines. (Actually that's a lie, you can use straight lines too.)

It is pure Elixir, with no dependencies, and fast: solving a point takes a fraction of a microsecond.

Install

def deps do
  [
    {:curves, "~> 1.0"}
  ]
end

Your first curve in two lines

curve = Curves.define_bezier(:ease_in_out)
Curves.Svg.save!(curve, "ease_in_out.svg")

The blue line is the curve. The orange dots are the points that shape it: the curve starts at the first, ends at the last, and is pulled towards the ones in between.

Finding a point: t

Every curve travels from start to end, and t is the percentage of progress along the segment. t goes from 0.0 to 1.0. and Curves.solve!/2 tells you where you are:

Curves.solve!(curve, 0.5)
#=> {0.5, 0.5}

Longer paths: splines

A single Bezier curve has at most 4 points. For longer paths, a spline joins many curves into one. This one passes through every point you give it:

curve = Curves.define_catmull_rom([{0, 0}, {2, 3}, {4, 1}, {6, 4}, {8, 2}])
Curves.solve!(curve, 2.5)

Where to next

The tutorial takes about 15 minutes and is full of pictures:

1. Your first curve: t, solve, take, and the ready-made curves.
2. Bezier curves: how control points shape a curve.
3. Splines: polylines and the nine kinds of spline, and when to use each.
4. Transforms and drawing: moving, scaling and rotating curves, and drawing them.

Not sure which curve you need? Choosing a curve compares them all, with real-world examples of where each one is used.

Prefer to play? Each chapter is also an interactive Livebook with sliders and animations; look for the "Run in Livebook" button on the interactive version of chapter 1.

The full API is in the Curves module.