v1.1.5

• Fix error trying to interpolate objects without prototypes. Thanks, @devgru! (#35)

v1.1.4

• Update dependencies.

v1.1.3

• Fix d3.interpolateRgb.gamma’s opacity interpolation. (#31)

v1.1.2

• Update dependencies.

v1.1.1

• Add module entry point to package.json.

v1.1.0

• Add d3.interpolateDate.
• Change d3.interpolate to special-case dates (#24).
• Change d3.interpolate to special-case number-like objects (#24).

v1.0.1

• Fix parsing of SVG transforms in IE (#22).

v1.0.0

• First stable release.

Changes since D3 3.x

The d3.interpolate method no longer delegates to d3.interpolators, which has been removed; its behavior is now defined by the library. It is now slightly faster in the common case that b is a number. It only uses d3.interpolateRgb if b is a valid CSS color specifier (and not approximately one). And if the end value b is null, undefined, true or false, d3.interpolate now returns a constant function which always returns b.

The behavior of d3.interpolateObject and d3.interpolateArray has changed slightly with respect to properties or elements in the start value a that do not exist in the end value b: these properties and elements are now ignored, such that the ending value of the interpolator at t = 1 is now precisely equal to b. So, in 3.x:

d3.interpolateObject({foo: 2, bar: 1}, {foo: 3})(0.5); // {bar: 1, foo: 2.5} in 3.x

Whereas in 4.0, a.bar is ignored:

d3.interpolateObject({foo: 2, bar: 1}, {foo: 3})(0.5); // {foo: 2.5} in 4.0

If a or b are undefined or not an object, they are now implicitly converted to the empty object or empty array as appropriate, rather than throwing a TypeError.

The d3.interpolateTransform interpolator has been renamed to d3.interpolateTransformSvg, and there is a new d3.interpolateTransformCss to interpolate CSS transforms! This allows d3-transition to automatically interpolate both the SVG transform attribute and the CSS transform style property. (Note, however, that only 2D CSS transforms are supported.) The d3.transform method has been removed.

Color space interpolators now interpolate opacity (see d3-color) and return rgb(…) or rgba(…) CSS color specifier strings rather than using the RGB hexadecimal format. This is necessary to support opacity interpolation, but is also beneficial because it matches CSS computed values. When a channel in the start color a is undefined, color interpolators now use the corresponding channel value from the end color b, or vice versa. This logic previously applied to some channels (such as saturation in HSL), but now applies to all channels in all color spaces, and is especially useful when interpolating to or from transparent.

There are now “long” versions of cylindrical color space interpolators: d3.interpolateHslLong, d3.interpolateHclLong and d3.interpolateCubehelixLong. These interpolators use linear interpolation of hue, rather than using the shortest path around the 360° hue circle. See d3.interpolateRainbow for an example. The Cubehelix color space is now supported by d3-color, and so there are now d3.interpolateCubehelix and d3.interpolateCubehelixLong interpolators.

Gamma-corrected color interpolation is now supported for both RGB and Cubehelix color spaces as interpolate.gamma. For example, to interpolate from purple to orange with a gamma of 2.2 in RGB space:

var interpolate = d3.interpolateRgb.gamma(2.2)("purple", "orange");

There are new interpolators for uniform non-rational B-splines! These are useful for smoothly interpolating between an arbitrary sequence of values from t = 0 to t = 1, such as to generate a smooth color gradient from a discrete set of colors. The d3.interpolateBasis and d3.interpolateBasisClosed interpolators generate one-dimensional B-splines, while d3.interpolateRgbBasis and d3.interpolateRgbBasisClosed generate three-dimensional B-splines through RGB color space. These are used by d3-scale-chromatic to generate continuous color scales from ColorBrewer’s discrete color schemes, such as PiYG.

There’s also now a d3.quantize method for generating uniformly-spaced discrete samples from a continuous interpolator. This is useful for taking one of the built-in color scales (such as d3.interpolateViridis) and quantizing it for use with d3.scaleQuantize, d3.scaleQuantile or d3.scaleThreshold.

See CHANGES for all D3 changes since 3.x.

v0.9.0

• Export to the global d3 in vanilla environments (d3/d3#2840).

v0.8.3

• Add d3.quantize.