ExponentialGridLines:
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ExponentialGridLines

Calculates the numerical values suitable for exponentially-spaced grid lines to be used for plotting or other UI elements.
Location: NOT INSTALLED!

Description

ExponentialGridLines is a strategy object that finds suitable intervals for plotting grid lines and labels. The values span the range defined by a corresponding ControlSpec. Most of the functionality of ExponentialGridLines is inherited from its superclass, AbstractGridLines. The instance methods are used by DrawGrid (which is in turn used by Plotter) which handles the drawing of the lines and labels.

ExponentialGridLines isn't usually instantiated directly, but rather by the GridLines factory class or the ControlSpec: -grid method which return the appropriate AbstractGridLines subclass for the given spec.

Class Methods

.new

Arguments:

spec

A ControlSpec that defines the numerical range, warp, and step.

Returns:

An instance of this class.

NOTE: AbstractGridLines shouldn't be instantiated directly. Instead, the GridLines factory class or the ControlSpec: -grid method should be used to return the appropriate AbstractGridLines subclass.

Inherited class methods

Instance Methods

.spec

Get/set the ControlSpec that defines the numerical range, warp, and step.

Returns:

.asGrid

Return this object.

Discussion:

nil.asGrid returns a BlankGridLines (a subclass of AbstractGridLines) which produces no drawn lines. So if nil is passed to the grid argument of DrawGrid, no lines are drawn on the corresponding axis.

.niceNum

Rounds a value to a logical "nice number" that is within the same order of magnitude. See the discussion below for details.

Arguments:

val

The value you'd like to make nicer.

round

A boolean. Roughly speaking, rounding will allow the returned number to be above or below the input val (similar to a round operation), while when false the returned number will tend to be higher than val (similar to ceil).

Returns:

The nice number.

Discussion:

This method is used to support internal calculations for determining grid line values, though it may be useful for other applications.

Observe the rounding behavior:

The implementation is based on: A. S. Glassner, Ed., Graphics Gems. San Diego: Morgan Kaufmann, 1990.

.looseRange

Returns the logical minimum and maximum that will contain the min and max, determed internally using -niceNum.

Arguments:

min

Minimum value to include in the returned range.

max

Maximum value to include in the returned range.

ntick

The number of lines ("ticks") you would like within the range of [min, max], default: 5.

Returns:

An Array with the lower and upper bounds of the range containing your min and max, i.e. [rangeMin, rangeMax].

.getParams

Specifically for use by DrawGrid. This returns a Dictionary with keys: 'lines', an array of values where lines should be drawn, and 'labels', an array of 2-element arrays [value, "formatted label"] for each line.

Note that the highest and lowest values returned don't necessarily contain your valueMin and valueMax, but rather represent the values where grid lines will be drawn by DrawGrid (endcap lines are subsequently drawn at the data/grid bounds).

Arguments:

valueMin

Minimum value of the data to be plotted. The lowest grid line value returned may be higher than this value.

valueMax

Maximum value of the data to be plotted. The highest grid line value returned may be lower than this value.

pixelMin

Lower bound of the grid's range, in pixels. Used to calculate the size of the available grid space when determining grid values based on tickSpacing (if numTicks is nil).

pixelMax

Upper bound of the grid's range, in pixels. Used to calculate the size of the available grid space when determining grid values based on tickSpacing (if numTicks is nil).

numTicks

Explicit number of ticks you would like to see on the graph (though the result is approximate). Set to nil if you'd like the number of ticks to be found automatically, based on pixelMin, pixelMax, and tickSpacing.

tickSpacing

Minimum distance between ticks (in pixels). This value is only used when numTicks is nil.

Returns:

.formatLabel

Format a numerical value for display as text, rounded to a desired precision.

Arguments:

val

The value to round and convert to a text label.

numDecimalPlaces

Number of decimal places to represent in the returned String.

Returns:

A String.

Inherited instance methods