Graph margin axis MARGINAXIS command

Commands in this namespace document the logical margin-axis commands of graph, barchart, stripchart, and polar widgets.

MARGINAXIS is used below as a placeholder for any of:

GRAPHINST xaxis
GRAPHINST x2axis
GRAPHINST yaxis
GRAPHINST y2axis

For example:

graph .g

.g xaxis configure -title "Time"
.g yaxis configure -title "Voltage"

These commands operate on axes assigned to one of the graph’s four logical axis positions.

Logical and physical margins

With the normal graph orientation, the logical axes correspond to the following physical margins:

Command	Physical margin
xaxis	bottom
x2axis	top
yaxis	left
y2axis	right

When the graph is configured with -invertxy yes, the logical X and Y directions are exchanged and the physical margins become:

Command	Physical margin with -invertxy yes
xaxis	left
x2axis	right
yaxis	bottom
y2axis	top

Application code can therefore continue to use xaxis and yaxis as logical X and Y interfaces regardless of graph orientation.

Assigned axes

Each margin can contain one or more virtual axes. The use operation queries or changes the ordered list of axes assigned to the margin.

For example:

.g axis create time
.g axis create phase

.g xaxis use {time phase}

The order is significant. The first axis in the list is the primary axis for that margin and is the axis addressed by the other MARGINAXIS operations such as configure, cget, transform, and limits.

Additional axes in the list are displayed farther away from the plotting area.

Querying use returns the complete ordered list:

.g xaxis use
# -> time phase

Assigning an axis to a new margin removes it from its previous margin.

An axis assigned through xaxis or x2axis must be an X-type axis. An axis assigned through yaxis or y2axis must be a Y-type axis. A previously untyped virtual axis acquires the required type when it is assigned.

An empty list removes all axes from the margin:

.g x2axis use {}

Axis configuration

Margin axes use exactly the same axis configuration options as virtual axes.

See AXIS for the complete axis option reference and for detailed descriptions of axis ranges, logarithmic scaling, ticks, labels, scrolling, bindings, and automatic range handling.

For example:

.g xaxis configure -title {Frequency (Hz)} -logscale yes -min 1 -max 1e9

This is equivalent to configuring the first virtual axis currently assigned to the logical X-axis margin.

Coordinate conversion

transform and invtransform use the first axis assigned to the margin.

transform converts a graph-coordinate value to the corresponding window coordinate:

set pixel [.g xaxis transform 10.0]

invtransform performs the reverse operation:

set value [.g xaxis invtransform $pixel]

The axis orientation, -descending setting, logarithmic mapping, and graph -invertxy setting are handled automatically.

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Copyright (c) George Yashin