Add custom minor tick class for polar plots

Author: ChristosT

hexrdgui/image_canvas.py

@@ -1,5 +1,6 @@
 import copy
 import math
+import logging
 
 from PySide6.QtCore import QThreadPool, QTimer, Signal, Qt
 from PySide6.QtWidgets import QFileDialog, QMessageBox
@@ -10,6 +11,7 @@
 from matplotlib.patches import Circle
 from matplotlib.ticker import AutoLocator, AutoMinorLocator, FuncFormatter
 
+import matplotlib as mpl
 import matplotlib.pyplot as plt
 import matplotlib.transforms as tx
 
@@ -1042,7 +1044,7 @@ def finish_show_polar(self, iviewer):
                 self.axis.yaxis.set_minor_locator(AutoMinorLocator())
 
                 self.axis.xaxis.set_major_locator(PolarXAxisTickLocator(self))
-                self.axis.xaxis.set_minor_locator(AutoMinorLocator())
+                self.axis.xaxis.set_minor_locator(PolarXAxisMinorTickLocator(self))
 
                 kwargs = {
                     'left': True,
@@ -1103,7 +1105,7 @@ def finish_show_polar(self, iviewer):
                 axis.yaxis.set_minor_locator(AutoMinorLocator())
 
                 axis.xaxis.set_major_locator(PolarXAxisTickLocator(self))
-                axis.xaxis.set_minor_locator(AutoMinorLocator())
+                self.axis.xaxis.set_minor_locator(PolarXAxisMinorTickLocator(self))
 
                 # change property of ticks
                 kwargs = {
@@ -1836,6 +1838,61 @@ def tick_values(self, vmin, vmax):
         # Convert back to tth
         return canvas.polar_x_type_to_tth(values)
 
+class PolarXAxisMinorTickLocator(AutoMinorLocator):
+    """Subclass the tick locator so we can modify its behavior
+
+    We will modify any value ranges provided so that the current x-axis type
+    provides nice looking ticks.
+
+    For instance, for Q, we want to space minor ticks non-linearly between major ticks
+    """
+    def __init__(self, canvas, *args, **kwargs):
+        super().__init__(*args, **kwargs)
+        self._hexrdgui_canvas = canvas
+
+    def __call__(self):
+        canvas = self._hexrdgui_canvas
+        if self.axis.get_scale() == 'log':
+            logging.warning('PolarXAxisMinorTickLocator does not work on logarithmic scales')
+            return []
+
+        majorlocs = np.unique(self.axis.get_majorticklocs())
+        if len(majorlocs) < 2:
+            # Need at least two major ticks to find minor tick locations.
+            # TODO: Figure out a way to still be able to display minor ticks with less
+            # than two major ticks visible. For now, just display no ticks at all.
+            return []
+
+        # Convert to our current x type
+        majorlocs = canvas.polar_tth_to_x_type(majorlocs)
+        majorstep = majorlocs[1] - majorlocs[0]
+
+        if self.ndivs is None:
+            self.ndivs = mpl.rcParams[
+                'ytick.minor.ndivs' if self.axis.axis_name == 'y'
+                else 'xtick.minor.ndivs']  # for x and z axis
+
+        if self.ndivs == 'auto':
+            majorstep_mantissa = 10 ** (np.log10(majorstep) % 1)
+            ndivs = 5 if np.isclose(majorstep_mantissa, [1, 2.5, 5, 10]).any() else 4
+        else:
+            ndivs = self.ndivs
+
+        minorstep = majorstep / ndivs
+
+        vmin, vmax = sorted(self.axis.get_view_interval())
+        # Convert to our current x type
+        vmin, vmax = canvas.polar_tth_to_x_type([vmin, vmax])
+        t0 = majorlocs[0]
+        tmin = round((vmin - t0) / minorstep)
+        tmax = round((vmax - t0) / minorstep) + 1
+        locs = (np.arange(tmin, tmax) * minorstep) + t0
+
+        # Convert back to tth
+        locs = canvas.polar_x_type_to_tth(locs)
+
+        return self.raise_if_exceeds(locs)
+
 
 class PolarXAxisFormatter(FuncFormatter):
     """Subclass the func formatter so we can keep the default formatter in sync