marker-lines

Arguments: chart-axis

Returns the marker-lines property of a chart-axis object, which is associated with a chart-widget or plot-widget control. The value may be set at creation time by passing the :marker-lines initarg to make-instance, or any time later by calling (setf marker-lines).

Marker lines are straight line segments or thicker bands that are drawn perpendicular to a chart axis. Each line or band is drawn outward from a specified value (for a line) or range of values (for a band) along the axis, to highlight an arbitrary set of values.

An example would be a chart of economic statistics, where the item-axis represents time and has bands extending from it to mark where recessions have occurred in the past.

There are no entries in the chart legend for marker-lines. Their meaning could be noted in the subtitle or footnote text of a chart.

The value of the property should be a list of lists, where each sublist is a property list that describes one line or band to draw perpendicular to the axis. Here are the valid keys for each property list, and the type of value to specify for each one:

• :value: every sublist should have a :value entry that specifies the point along the axis at which to draw a line or band. The value should be a real number (either an integer or not).
• :value-to: if there is a :value-to entry, then a band will be drawn between the :value value to the :value-to value. Otherwise a line will be drawn at the :value value. The value should be a real number (either an integer or not).
• :color: this is the color in which to draw the line or band. The value should be an RGB object (see make-rgb) or a symbol whose value is an RGB. When unspecified, the color will default to red for lines and light-gray for bands.
• :line-width: this is the thickness (measured in pixels) with which to draw the line, when no :value-to is specified for a band. The value should be a positive integer. When unspecified, it defaults to 1.
• :line-dashing: this is the dashing style with which to draw the line, when no :value-to is specified for a band. The value should be one of the keyword symbols that are valid values for the line-dashing property of a stream, such as :solid or :dash. When unspecified, it defaults to :solid.

Here is a sample value of the marker-lines property of an axis that would draw two lines and two bands:

((:value 3.5 :color blue :line-width 5 :line-dashing :dot)
 (:value 6)
 (:value 7 :value-to 8.5)
 (:value 10.4 :value-to 15 :color cyan))

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This page was not revised from the 8.2 page.
Created 2012.5.30.