Use width and height attributes instead of size, for consistency with other
chart templates. (Though, note that chart templates are inconsistent with
layouts in this regard, which use a size property. But let's remain locally
consistent for now.) Default x and y properties to [0] and [1] to match the
defaults of d3.svg.area.
Add support for mode and interpolate properties. The mode can be either "offset"
or "mirror", with the default being "offset". The interpolate property is the
same as that used by d3.svg.area, and defaults to "linear".
The horizon chart now properly clips the horizon layers, such that if a horizon
chart is use within a larger SVG element, it will not extend the chart bounds.
In addition, this commit fixes a bug in how unique IDs are assigned to the clip
and area paths; it's a shame that SVG does not support a way to refer to paths
locally.
Note that because negative values are offset or mirrored, the horizon chart will
render twice as many paths (use elements) as the requested number of bands. For
example, if the default bands of 1 is used, there will be one negative band and
one positive band. In the data has no negative values, then the negative band
will be empty. Keep this in mind as it affects the layer's class attribute
(such as "q0-3" and "q2-3" for the default single-band horizon).
The data join is now specified as a single function of data, as with all other
properties. This allows the key to be computed on the previously-bound data,
rather than requiring the key to be serialized into the DOM (say, as an
attribute). In the case that there is no previously-bound data, it is still
possible to access the associated node as the `this` context.
The `enter` operator no longer performs an append. For symmetry with the `exit`
operator, you must call `append` after obtaining the entering selection. This
requires a tiny bit more code, but should make the code more clear. Also, it
provides an opportunity to use a different instantiation operator, such as the
new `insert` operator. This takes a second argument, which is a selector for the
insert-before reference element. For example, the selector ":first-child" will
prepend nodes.
The `empty` operator allows you to query whether a selection is empty (i.e.,
contains zero matching nodes).
Mike Bostock
Jason Davies