Crosshair ornl (#39268)

### Description of work
copy of PR [39242](#39242)
into ORNL next
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Author: KyleQianliMa

docs/source/release/v6.13.0/Workbench/New_features/39242.rst

@@ -0,0 +1 @@
+- A crosshair toggle option has been added in mantidplots on the top right of the toolbar area. THe crosshair button is disabled (invisible) in titled plots.

qt/applications/workbench/workbench/plotting/figuremanager.py

@@ -232,6 +232,7 @@ def __init__(self, canvas, num):
             self.toolbar.sig_waterfall_conversion.connect(self.update_toolbar_waterfall_plot)
             self.toolbar.sig_change_line_collection_colour_triggered.connect(self.change_line_collection_colour)
             self.toolbar.sig_hide_plot_triggered.connect(self.hide_plot)
+            self.toolbar.sig_crosshair_toggle_triggered.connect(self.crosshair_toggle)
             self.toolbar.setFloatable(False)
             tbs_height = self.toolbar.sizeHint().height()
         else:
@@ -603,6 +604,41 @@ def _reverse_axis_lines(ax):
             line.remove()
             ax.add_line(line)
 
+    def crosshair_toggle(self, on):
+        cid = self.canvas.mpl_connect("motion_notify_event", self.crosshair)
+        if not on:
+            self.canvas.mpl_disconnect(cid)
+
+    def crosshair(self, event):
+        axes = self.canvas.figure.gca()
+
+        # create a crosshair made from horizontal and verticle lines.
+        self.horizontal_line = axes.axhline(color="r", lw=1.0, ls="-")
+        self.vertical_line = axes.axvline(color="r", lw=1.0, ls="-")
+
+        def set_cross_hair_visible(visible):
+            need_redraw = self.horizontal_line.get_visible() != visible
+            self.horizontal_line.set_visible(visible)
+            self.vertical_line.set_visible(visible)
+            return need_redraw
+
+        # if event is out-of-bound we update
+        if not event.inaxes:
+            need_redraw = set_cross_hair_visible(False)
+            if need_redraw:
+                axes.figure.canvas.draw()
+
+        else:
+            set_cross_hair_visible(True)
+            x, y = event.xdata, event.ydata
+            self.horizontal_line.set_ydata([y])
+            self.vertical_line.set_xdata([x])
+            self.canvas.draw()
+
+        # after update we remove
+        self.horizontal_line.remove()
+        self.vertical_line.remove()
+
 
 # -----------------------------------------------------------------------------
 # Figure control

qt/applications/workbench/workbench/plotting/test/test_toolbar.py

@@ -8,6 +8,7 @@
 
 import unittest
 from unittest.mock import patch
+import numpy as np
 
 import matplotlib
 
@@ -19,7 +20,7 @@
 from workbench.plotting.figuremanager import MantidFigureCanvas, FigureManagerWorkbench
 from workbench.plotting.toolbar import WorkbenchNavigationToolbar
 from mantid.plots.plotfunctions import plot
-from mantid.simpleapi import CreateSampleWorkspace, CreateMDHistoWorkspace
+from mantid.simpleapi import CreateSampleWorkspace, CreateMDHistoWorkspace, Load
 
 
 @start_qapplication
@@ -117,6 +118,39 @@ def test_button_checked_for_plot_with_grid(self, mock_qappthread):
         # Grid button should be ON because we enabled the grid.
         self.assertTrue(self._is_grid_button_checked(fig))
 
+    @patch("workbench.plotting.figuremanager.QAppThreadCall")
+    def test_button_checked_for_plot_with_no_crosshair(self, mock_qappthread):
+        mock_qappthread.return_value = mock_qappthread
+
+        fig, axes = plt.subplots(subplot_kw={"projection": "mantid"})
+        axes.plot([-10, 10], [1, 2])
+        # crosshair button should be OFF because we have not enabled the crosshair.
+        self.assertFalse(self._is_crosshair_button_checked(fig))
+        # crosshair button should be visible when there is only 1 axis
+        self.assertTrue(self._is_crosshair_button_visible(fig))
+
+    @patch("workbench.plotting.figuremanager.QAppThreadCall")
+    def test_button_hiden_for_tiled_plots(self, mock_qappthread):
+        mock_qappthread.return_value = mock_qappthread
+
+        fig, axes = plt.subplots(2)
+        axes[0].plot([-10, 10], [1, 2])
+        axes[1].plot([3, 2, 1], [1, 2, 3])
+        # crosshair button should be hidden because this is a tiled plot
+        self.assertFalse(self._is_crosshair_button_visible(fig))
+        self.assertFalse(self._is_crosshair_button_checked(fig))
+
+    @patch("workbench.plotting.figuremanager.QAppThreadCall")
+    def test_button_enabled_for_contour_plots(self, mock_qappthread):
+        mock_qappthread.return_value = mock_qappthread
+        data = Load("SANSLOQCan2D.nxs")
+        fig, axes = plt.subplots(subplot_kw={"projection": "mantid"})
+        axes.imshow(data, origin="lower", cmap="viridis", aspect="auto")
+        axes.contour(data, levels=np.linspace(10, 60, 6), colors="yellow", alpha=0.5)
+        # crosshair button should be visible because this is a contour plot
+        self.assertTrue(self._is_crosshair_button_visible(fig))
+        self.assertFalse(self._is_crosshair_button_checked(fig))
+
     @patch("workbench.plotting.figuremanager.QAppThreadCall")
     def test_button_checked_for_plot_with_grid_using_kwargs(self, mock_qappthread):
         mock_qappthread.return_value = mock_qappthread
@@ -266,6 +300,32 @@ def _is_button_enabled(cls, fig, button):
         fig_manager.toolbar.set_buttons_visibility(fig)
         return fig_manager.toolbar._actions[button].isEnabled()
 
+    @classmethod
+    def _is_crosshair_button_checked(cls, fig):
+        """
+        Create the figure manager and check whether its toolbar is toggled on or off for the given figure.
+        We have to explicitly call set_button_visibility() here, which would otherwise be called within the show()
+        function.
+        """
+        canvas = MantidFigureCanvas(fig)
+        fig_manager = FigureManagerWorkbench(canvas, 1)
+        # This is only called when show() is called on the figure manager, so we have to manually call it here.
+        fig_manager.toolbar.set_buttons_visibility(fig)
+        return fig_manager.toolbar._actions["toggle_crosshair"].isChecked()
+
+    @classmethod
+    def _is_crosshair_button_visible(cls, fig):
+        """
+        Create the figure manager and check whether its toolbar is visible for the given figure.
+        We have to explicitly call set_button_visibility() here, which would otherwise be called within the show()
+        function.
+        """
+        canvas = MantidFigureCanvas(fig)
+        fig_manager = FigureManagerWorkbench(canvas, 1)
+        # This is only called when show() is called on the figure manager, so we have to manually call it here.
+        fig_manager.toolbar.set_buttons_visibility(fig)
+        return fig_manager.toolbar._actions["toggle_crosshair"].isVisible()
+
 
 if __name__ == "__main__":
     unittest.main()

qt/applications/workbench/workbench/plotting/toolbar.py

@@ -35,6 +35,7 @@ def _create_script_action(self, text, tooltip_text, mdi_icon, *args):
 class WorkbenchNavigationToolbar(MantidNavigationToolbar):
     sig_home_clicked = QtCore.Signal()
     sig_grid_toggle_triggered = QtCore.Signal(bool)
+    sig_crosshair_toggle_triggered = QtCore.Signal(bool)
     sig_active_triggered = QtCore.Signal()
     sig_hold_triggered = QtCore.Signal()
     sig_toggle_fit_triggered = QtCore.Signal()
@@ -84,6 +85,7 @@ class WorkbenchNavigationToolbar(MantidNavigationToolbar):
         MantidNavigationTool("Fill Area", "Fill area under curves", "mdi.format-color-fill", "waterfall_fill_area", None),
         MantidStandardNavigationTools.SEPARATOR,
         MantidNavigationTool("Help", "Open plotting help documentation", "mdi.help", "launch_plot_help", None),
+        MantidNavigationTool("Crosshair", "Toggle crosshair", "mdi.plus", "toggle_crosshair", False),
         MantidNavigationTool("Hide", "Hide the plot", "mdi.eye", "hide_plot", None),
     )
 
@@ -94,6 +96,20 @@ def __init__(self, canvas, parent, coordinates=True):
         dpi_ratio = QtWidgets.QApplication.instance().desktop().physicalDpiX() / 100
         self.setIconSize(QtCore.QSize(int(24 * dpi_ratio), int(24 * dpi_ratio)))
 
+    def toggle_crosshair(self, enable=None):
+        if enable is None:
+            enable = self._actions["toggle_crosshair"].isChecked()
+        else:
+            self._actions["toggle_crosshair"].setChecked(enable)
+        self.sig_crosshair_toggle_triggered.emit(enable)
+
+    def set_crosshair_enabled(self, on):
+        action = self._actions["toggle_crosshair"]
+        action.setEnabled(on)
+        action.setVisible(on)
+        # Show/hide the separator between this button and help button / waterfall options
+        self.toggle_separator_visibility(action, on)
+
     def hide_plot(self):
         self.sig_hide_plot_triggered.emit()
 
@@ -217,6 +233,11 @@ def set_buttons_visibility(self, fig):
         if figure_type(fig) not in [FigureType.Line, FigureType.Errorbar] or len(fig.get_axes()) > 1:
             self.set_fit_enabled(False)
             self.set_superplot_enabled(False)
+
+        # disable crosshair in tiled plots but keep it enabled in color contour plot
+        if len(fig.get_axes()) > 1 and figure_type(fig) not in [FigureType.Contour]:
+            self.set_crosshair_enabled(False)
+
         for ax in fig.get_axes():
             for artist in ax.get_lines():
                 try: