"""
Line fronts
-----------

Using the :meth:`pygmt.Figure.plot` method you can draw a so-called
*front* which allows to plot specific symbols distributed along a line
or curve. Typical use cases are weather fronts, fault lines,
subduction zones, and more.

A front can be drawn by passing **f**\[±]\ *gap*\[/*size*] to the ``style``
parameter where *gap* defines the distance gap between the symbols and
*size* the symbol size. If *gap* is negative, it is interpreted to mean
the number of symbols along the front instead. If *gap* has a leading +
then we use the value exactly as given [Default will start and end each
line with a symbol, hence the *gap* is adjusted to fit]. If *size* is
missing it is set to 30% of the *gap*, except when *gap* is negative
and *size* is thus required. Append **+l** or **+r** to plot symbols on
the left or right side of the front [Default is centered]. Append
**+**\ *type* to specify which symbol to plot: **b**\ ox, **c**\ ircle,
**f**\ ault (default), **s**\ lip, or **t**\ riangle. Slip means left-lateral
or right-lateral strike-slip arrows (centered is not an option). The **+s**
modifier optionally accepts the angle used to draw the vector (default is
20). Alternatively, use **+S** which draws arcuate arrow heads. Append
**+o**\ *offset* to offset the first symbol from the beginning of the front
by that amount (default is 0). The chosen symbol is drawn with the same pen
as set for the line (i.e., via the ``pen`` parameter). To use an alternate
pen, append **+p**\ *pen*. To skip the outline, just use **+p** with no
argument. To make the main front line invisible, add **+i**.

"""

import numpy as np
import pygmt

# Generate a two-point line for plotting
x = np.array([1, 4])
y = np.array([20, 20])

fig = pygmt.Figure()
fig.basemap(region=[0, 10, 0, 20], projection="X15c/15c", frame='+t"Line Fronts"')

# Plot the line using different front styles
for frontstyle in [
    # line with "faults" front style, same as +f (default)
    "f1c/0.25c",
    # line with box front style
    "f1c/0.25c+b",
    # line with circle front style
    "f1c/0.25c+c",
    # line with triangle front style
    "f1c/0.3c+t",
    # line with left-lateral ("+l") slip ("+s") front style, angle is set to 45 and
    # offset to 2.25 cm
    "f5c/1c+l+s45+o2.25c",
    # line with "faults" front style, symbols are plotted on the left side of the front
    "f1c/0.4c+l",
    # line with box front style, symbols are plotted on the left side of the front
    "f1c/0.3c+l+b",
    # line with circle front style, symbols are plotted on the right side of the front
    "f1c/0.4c+r+c",
    # line with triangle front style, symbols are plotted on the left side of the front
    "f1c/0.3c+l+t",
    # line with triangle front style, symbols are plotted on the right side of the front
    # use other pen for the outline of the symbol
    "f1c/0.4c+r+t+p1.5p,dodgerblue",
    # line with triangle front style, symbols are plotted on the right side of the front
    # and offset is set to 0.3 cm, skip the outline
    "f0.5c/0.3c+r+t+o0.3c+p",
    # line with triangle front style, symbols are plotted on the right side of the front
    # and offset is set to 0.3 cm, skip the outline and make the main front line invisible
    "f0.5c/0.3c+r+t+o0.3c+p+i",
]:
    y -= 1  # move the current line down
    fig.plot(x=x, y=y, pen="1.25p", style=frontstyle, color="red3")
    fig.text(
        x=x[-1],
        y=y[-1],
        text=frontstyle,
        font="Courier-Bold",
        justify="ML",
        offset="0.75c/0c",
    )

fig.show()

Add a gallery example showing different front styles (#1022)