extend-data-to-middle-of-border

Arguments: chart-or-plot

Returns the value of the extend-data-to-middle-of-border property of a chart-or-plot. The value may be set at creation time by passing the :extend-data-to-middle-of-border initarg, or any time later by calling (setf extend-data-to-middle-of-border).

A boolean value indicating whether the data area of a chart-or-plot extends to the middle of the body border rather than only to the inner edge of the body border. This choice is a subtle trade-off in the aesthetics of how a chart is drawn, where neatly aligning end tic marks with axes means that data will extend into the middle of a thick axis. The default value is t for just that choice.

This property matters most when a chart body border is thick, and is best described by example. Let's assume that the chart-orientation is :vertical (meaning that the value axis is vertical), that the axis-width of the horizontal item-axis is 7, that the range-bottom of the value-axis is zero, and that a data value of zero is being plotted.

In this example, if extend-data-to-middle-of-border is nil, then a line that is drawn downward to the zero data point will be drawn just to the top of the thick item-axis along the bottom of the chart. Any icon for the zero data point will be centered at the top of the thick item-axis line as well. If this property is true instead, then the line will extend four pixels farther downward to the middle of the thick item axis, and any icon would be centered about the middle of the axis.

A thick tic mark on the vertical value axis will always be vertically centered about the data value to which it points. So if the value of this property is nil, then a thick tic mark at the bottom of the value axis will appear jogged upward from the horizontal item-axis a bit so that its center is aligned with the top of the item-axis, because that is where a data value of zero is plotted. That tends to look a bit sloppy, so the default value of this property is true to instead align a thick end tic mark exactly with an axis of the same thickness. The trade-off is that this causes data values to extend to the middle of the item-axis, which may obscure the data somewhat.

See chart-widget and also cg-chart-widget.htm.

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Created 2010.1.21.