d4_interpolate library

Interpolate numbers, colors, strings, lists, maps, whatever!

This package provides a variety of interpolation methods for blending between two values. Values may be numbers, colors, strings, lists, or even deeply-nested maps. For example:

final i = interpolateNumber(10, 20);
i(0.0); // 10
i(0.2); // 12
i(0.5); // 15
i(1.0); // 20

The returned function i is called an interpolator. Given a starting value a and an ending value b, it takes a parameter t in the domain [0, 1] and returns the corresponding interpolated value. An interpolator typically returns a value equivalent to a at t = 0 and a value equivalent to b at t = 1.

You can interpolate more than just numbers. To find the perceptual midpoint between steelblue and brown:

interpolateLab("steelblue", "brown")(0.5); // rgb(142, 92, 109)

Or, as a color ramp from t = 0 to t = 1:

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Here’s a more elaborate example demonstrating type inference used by interpolate:

final i = interpolate({"colors": ["red", "blue"]}, {"colors": ["white", "black"]});
i(0.0); // {colors: [rgb(255, 0, 0), rgb(0, 0, 255)]}
i(0.5); // {colors: [rgb(255, 128, 128), rgb(0, 0, 128)]}
i(1.0); // {colors: [rgb(255, 255, 255), rgb(0, 0, 0)]}

Note that the generic value interpolator detects not only nested maps and lists, but also color strings and numbers embedded in strings!

Functions

interpolate(Object? a, Object? b) → Object? Function(num)

Returns an interpolator between the two arbitrary values a and b.

interpolateBasis(List<num> values) → num Function(num)

Returns a uniform nonrational B-spline interpolator through the specified list of values, which must be numbers.

interpolateBasisClosed(List<num> values) → num Function(num)

Returns a uniform nonrational B-spline interpolator through the specified list of values, which must be numbers.

interpolateCubehelix(Object? a, Object? b) → String Function(num)

Returns an Cubehelix color space interpolator between the two colors a and b with a default gamma of 1.

interpolateCubehelixGamma(num gamma) → String Function(num) Function(Object?, Object?)

Returns a new Cubehelix color space interpolator factory using the specified gamma.

interpolateCubehelixGammaLong(num gamma) → String Function(num) Function(Object?, Object?)

Like interpolateCubehelixGamma, but does not use the shortest path between hues.

interpolateCubehelixLong(Object? a, Object? b) → String Function(num)

Like interpolateCubehelixGammaLong, but does not use the shortest path between hues.

interpolateDate(DateTime a, DateTime b) → DateTime Function(num)

Returns an interpolator between the two dates a and b.

interpolateDiscrete(List<Object?> values) → Object? Function(num)

Returns a discrete interpolator for the given list of values.

interpolateHcl(Object? a, Object? b) → String Function(num)

Returns a CIELChab color space interpolator between the two colors a and b.

interpolateHclLong(Object? a, Object? b) → String Function(num)

Like interpolateHcl, but does not use the shortest path between hues.

interpolateHsl(Object? a, Object? b) → String Function(num)

Returns an HSL color space interpolator between the two colors a and b.

interpolateHslLong(Object? a, Object? b) → String Function(num)

Like interpolateHsl, but does not use the shortest path between hues.

interpolateHue(num a, num b) → num Function(num)

Returns an interpolator between the two hue angles a and b.

interpolateLab(Object? a, Object? b) → String Function(num)

Returns a CIELAB color space interpolator between the two colors a and b.

interpolateList<T>(List<T> a, List<T> b) → List<Object?> Function(num)

Returns an interpolator between the two lists a and b.

interpolateMap<K, V>(Map<K, V> a, Map<K, V> b) → Map<K, Object?> Function(num)

Returns an interpolator between the two objects a and b.

interpolateNumber(num a, num b) → num Function(num)

Returns an interpolator between the two numbers a and b.

interpolateNumberList<T extends num>(List<T> a, List<T> b) → List<T> Function(num)

Returns an interpolator between the two list of numbers a and b.

interpolateRgb(Object? a, Object? b) → String Function(num)

Returns an RGB color space interpolator between the two colors a and b with a default gamma of 1.

interpolateRgbBasis(List<Object?> colors) → String Function(num)

Returns a uniform nonrational B-spline interpolator through the specified list of colors, which are converted to RGB color space.

interpolateRgbBasisClosed(List<Object?> colors) → String Function(num)

Returns a uniform nonrational B-spline interpolator through the specified list of colors, which are converted to RGB color space.

interpolateRgbGamma(num y) → String Function(num) Function(Object?, Object?)

Returns a new RGB color space interpolator factory using the specified gamma.

interpolateRound(num a, num b) → int Function(num)

Returns an interpolator between the two numbers a and b; the interpolator is similar to interpolateNumber, except it will round the resulting value to the nearest integer.

interpolateString(String a, String b) → String Function(num)

Returns an interpolator between the two strings a and b.

interpolateZoom(View a, View b) → ZoomInterpolator

Returns an interpolator between the two views a and b of a two-dimensional plane, based on “Smooth and efficient zooming and panning” by Jarke J. van Wijk and Wim A.A. Nuij.

interpolateZoomRho(num rho) → ZoomInterpolator Function(View, View)

Returns a new zoom interpolator using the specified curvature rho.

piecewise<T>(List<T> values, [Object? Function(num) interpolatorFactory(T, T) = interpolate]) → Object? Function(num)

Returns a piecewise interpolator, composing interpolators for each adjacent pair of values.

quantize<T>(T interpolator(num), int n) → List<T>

Returns n uniformly-spaced samples from the specified interpolator, where n is an integer greater than one.