See [*line*.context](https://github.com/d3/d3-shape#line_context), [*area*.context](https://github.com/d3/d3-shape#area_context) and [*arc*.context](https://github.com/d3/d3-shape#arc_context) for more. Under the hood, this uses [d3-path](#paths-d3-path) to serialize canvas path methods to an SVG path data string when the context is null. Thus, shapes are optimized for rendering to canvas.
new curve API!
**line*.interpolate ↦ *line*.curve
**area*.interpolate ↦ *area*.curve
* "basis" ↦ d3.curveBasis
* "basis-closed" ↦ d3.curveBasisClosed
* "basis-open" ↦ d3.curveBasisOpen
* "bundle" ↦ d3.curveBundle, *bundle*.beta
4.0 introduces a new API for specifying how line and area shapes render curves between data points. The *line*.interpolate and *area*.interpolate methods have been replaced with [*line*.curve](https://github.com/d3/d3-shape#line_curve) and [*area*.curve](https://github.com/d3/d3-shape#area_curve). Curves are now implemented using the [curve interface](https://github.com/d3/d3-shape#custom-curves) rather than as a function that returns an SVG path data string; this allows curves to render to either SVG or Canvas. In addition, *line*.curve and *area*.curve now take a function which instantiates a curve for a given *context*, rather than a string. The full list of equivalents:
* linear ↦ [d3.curveLinear](https://github.com/d3/d3-shape#curveLinear)
