Add a gallery example showing how to use patterns via the "fill" parameter (or similiar parameters) (#2329)

Co-authored-by: Michael Grund <23025878+michaelgrund@users.noreply.github.com>
Co-authored-by: Dongdong Tian <seisman.info@gmail.com>

Author: 3 people

examples/gallery/symbols/patterns.py

@@ -0,0 +1,91 @@
+r"""
+Bit and Hachure Patterns
+------------------------
+
+PyGMT allows using bit or hachure patterns via the ``fill`` parameter
+or similar parameters:
+
+- :meth:`pygmt.Figure.coast`: Land and water masses via ``land`` and
+  ``water``, respectively
+- :meth:`pygmt.Figure.histogram`: Histogram bars via ``fill``
+- :meth:`pygmt.Figure.meca`: Focal mechanisms via ``compressionfill``
+  and ``extensionfill``
+- :meth:`pygmt.Figure.plot`: Symbols and polygons via ``fill``
+- :meth:`pygmt.Figure.rose`: Histogram sectors via ``fill``
+- :meth:`pygmt.Figure.solar`: Day-light terminators via ``fill``
+- :meth:`pygmt.Figure.ternary`: Symbols via ``fill``
+- :meth:`pygmt.Figure.velo`: Uncertainty wedges and velocity error
+  ellipses via ``uncertaintyfill``
+- :meth:`pygmt.Figure.wiggle`: Anomalies via ``fillpositive``
+  and ``fillnegative``
+
+The required argument has the following form:
+
+**P**\|\ **p**\ *pattern*\ [**+b**\ *color*][**+f**\ *color*][**+r**\ *dpi*]
+
+*pattern* can either be a number in the range 1-90 or the name of a
+1-, 8-, or 24-bit image raster file. The former will result in one of the 90
+predefined 64 x 64 bit-patterns provided by GMT; an overview can by found at
+https://docs.generic-mapping-tools.org/latest/cookbook/predefined-patterns.html.
+The latter allows the user to create customized, repeating images using image
+raster files.
+By specifying upper case **P** instead of **p** the image will be
+bit-reversed, i.e., white and black areas will be interchanged (only applies
+to 1-bit images or predefined bit-image patterns).
+For these patterns and other 1-bit images one may specify alternative
+**b**\ ackground and **f**\ oreground colors (by appending **+b**\ *color*
+and/or **+f**\ *color*) that will replace the default white and black pixels,
+respectively. Excluding *color* from a fore- or background specification yields
+a transparent image where only the back- or foreground pixels will be painted.
+The **+r**\ *dpi* modifier sets the resolution in dpi.
+"""
+
+import pygmt
+
+y = 11
+
+fig = pygmt.Figure()
+fig.basemap(
+    region=[0, 10, 0, 12],
+    projection="X10c",
+    frame="rlbt+glightgray+tBit and Hachure Patterns",
+)
+
+# To use a pattern as fill append "p" and the number of the desired
+# pattern. By default, the pattern is plotted in black and white
+# with a resolution of 300 dpi
+for pattern in [
+    # Plot a hachted pattern via pattern number 8
+    "p8",
+    # Plot a dotted pattern via pattern number 19
+    "p19",
+    # Set the background color ("+b") to "red3"
+    # and the foreground color ("+f") to "lightgray"
+    "p19+bred3+flightbrown",
+    # Invert the pattern by using a capitalized "P"
+    "P19+bred3+flightbrown",
+    # Change the resolution ("+r") to 100 dpi
+    "p19+bred3+flightbrown+r100",
+    # Make the background transparent by not giving a color after "+b";
+    # works analogous for the foreground
+    "p19+b+flightbrown+r100",
+]:
+    # Plot a square with the pattern as fill
+    fig.plot(
+        x=2,
+        y=y,
+        style="s2c",  # square with a width of 2 centimeters
+        pen="1p,black",  # 1 point thick, black outline
+        fill=pattern,
+    )
+    # Add a description of the pattern
+    fig.text(
+        x=4,
+        y=y,
+        text=pattern,
+        font="Courier-Bold",
+        justify="ML",  # justification of the text is Middle Left
+    )
+    y -= 2
+
+fig.show()