853 improve linebuilder (#854)

* add more features to linebuilder

* update ugrid mapnc example script

* updated whatsnew

dfm_tools/linebuilder.py

@@ -1,30 +1,86 @@
 import numpy as np
+import matplotlib.pyplot as plt
 
 __all__ = ["LineBuilder"]
 
 
 class LineBuilder:
     """
-    https://matplotlib.org/stable/users/explain/event_handling.html
+    To interactively draw a line in a figure axis, for instance to use as cross-section.
+    - ctrl+leftmouseclick to add a point to the line
+    - ctrl+rightmouseclick to remove the last point of the line
+    - ctrl+doublemouseclick to finish and let the script continue
     """
-    def __init__(self, line):
-        #self.waiting_for_entry = True
+    def __init__(self, ax=None):
+        print("draw a line in the figure interactively: ctrl+click to add point, ctrl+rightclick to undo, ctrl+doubleclick to finish")
+
+        # get current axis if not provided
+        if ax is None:
+            ax = plt.gca()
+
+        # initialize x/y arrays and line object
+        self.xs = []
+        self.ys = []
+        line, = ax.plot(self.xs, self.ys,'o-') # empty line
         self.line = line
-        self.xs = list(line.get_xdata())
-        self.ys = list(line.get_ydata())
-        self.cid = line.figure.canvas.mpl_connect('button_press_event', self)
-
-    def __call__(self, event):
-        print('click', event)
-        # if event.inaxes!=self.line.axes:
-        #     print('WARNING: that click was outside the figure axis')
-        #     return
-        # if event.dblclick:
-        #     print('WARNING: double click is interpreted as single click')
-        #     return
-        if event.inaxes!=self.line.axes: return
+
+        # register both button press events and key press events
+        self.cid_button = self.line.figure.canvas.mpl_connect('button_press_event', self.on_press)
+        self.cid_key = self.line.figure.canvas.mpl_connect('key_press_event', self.on_press)
+        # start a blocking event loop to prevent continuation of the script where LineBuilder was called
+        self.line.figure.canvas.start_event_loop()
+
+    @property
+    def line_array(self):
+        line_array = np.c_[self.xs, self.ys]
+        return line_array
+
+    def add_xy_to_line(self, event):
+        print(f"adding point: x={event.xdata:.6f}, y={event.ydata:.6f}")
         self.xs.append(event.xdata)
         self.ys.append(event.ydata)
-        self.line_array = np.c_[self.xs, self.ys]
         self.line.set_data(self.xs, self.ys)
         self.line.figure.canvas.draw()
+
+    def remove_last_xy_from_line(self, event):
+        print("removing last point if present")
+        self.xs = self.xs[:-1]
+        self.ys = self.ys[:-1]
+        self.line.set_data(self.xs, self.ys)
+        self.line.figure.canvas.draw()
+
+    def finish_linebuilder(self):
+        # disconnect the interactive line drawing in the figure
+        self.line.figure.canvas.mpl_disconnect(self.cid_button)
+        self.line.figure.canvas.mpl_disconnect(self.cid_key)
+        # let the rest of the script where LineBuilder was called continue
+        self.line.figure.canvas.stop_event_loop()
+        print("interactive line drawing finished")
+
+    def on_press(self, event):
+        # do nothing if ctrl is not pressed
+        if event.key != "control":
+            return
+
+        # do nothing if no mouse button is pressed
+        if not hasattr(event, "button"):
+            # key event has no button: AttributeError: 'KeyEvent' object has no attribute 'button'
+            return
+
+        # do nothing if mouse click is outside axis
+        if event.inaxes!=self.line.axes:
+            print('clicks outside of the figure axis are ignored')
+            return
+
+        # add new point to line and wrap up line upon "ctrl + left mouse double click"
+        if event.dblclick:
+            self.finish_linebuilder()
+            return
+
+        # add new point to line upon "ctrl + left mouse click"
+        if event.button == 1:
+            self.add_xy_to_line(event)
+
+        # remove last point from line upon "ctrl + right mouse click"
+        if event.button == 3:
+            self.remove_last_xy_from_line(event)

docs/whats-new.md

@@ -2,6 +2,9 @@
 
 ## UNRELEASED
 
+### Feat
+- improved usability of `dfmt.LineBuilder()` in [#854](https://github.com/Deltares/dfm_tools/pull/854)
+
 
 ## 0.23.0 (2024-05-15)
 

tests/examples/postprocess_mapnc_ugrid.py

@@ -169,10 +169,11 @@
     pc = data_frommap_merged['mesh2d_flowelem_bl'].ugrid.plot(cmap='jet') #TODO: default is edgecolor='face', should work even better with edgecolor='none', but that results in seethrough edges anyway, report to matplotlib?
     pc.set_clim(clim_bl)
     ax_input.set_aspect('equal')
-    line, = ax_input.plot([], [],'o-') # empty line
-    linebuilder = dfmt.LineBuilder(line) #this makes it possible to interactively click a line in the bedlevel figure. Use linebuilder.line_array as alternative line_array
+    # line_array is defined above, alternatively click a cross-section line_array in the figure interactively with dfmt.LineBuilder
+    # line_array = dfmt.LineBuilder(ax=ax_input).line_array
     ax_input.plot(line_array[0,0],line_array[0,1],'bx',linewidth=3,markersize=10)
     ax_input.plot(line_array[:,0],line_array[:,1],'b',linewidth=3)
+
     fig.tight_layout()
     fig.savefig(os.path.join(dir_output,f'{basename}_mesh2d_flowelem_bl'))
     if crs is not None: