Use scatter for check boxes instead of Rectangle

With the current implementation, the boxes get stretched into rectangles
if the aspect ratio is not maintained. To overcome this, the boxes are
now created using scatter instead to maintain their shapes.

Author: chahak13

lib/matplotlib/widgets.py

@@ -1002,43 +1002,24 @@ def __init__(self, ax, labels, actives=None):
         if actives is None:
             actives = [False] * len(labels)
 
-        if len(labels) > 1:
-            dy = 1. / (len(labels) + 1)
-            ys = np.linspace(1 - dy, dy, len(labels))
-        else:
-            dy = 0.25
-            ys = [0.5]
-
-        axcolor = ax.get_facecolor()
-
-        self.labels = []
-        self.lines = []
-        self.rectangles = []
-
-        lineparams = {'color': 'k', 'linewidth': 1.25,
-                      'transform': ax.transAxes, 'solid_capstyle': 'butt'}
-        for y, label, active in zip(ys, labels, actives):
-            t = ax.text(0.25, y, label, transform=ax.transAxes,
-                        horizontalalignment='left',
-                        verticalalignment='center')
-
-            w, h = dy / 2, dy / 2
-            x, y = 0.05, y - h / 2
-
-            p = Rectangle(xy=(x, y), width=w, height=h, edgecolor='black',
-                          facecolor=axcolor, transform=ax.transAxes)
+        ys = np.linspace(1, 0, len(labels)+2)[1:-1]
+        text_size = mpl.rcParams["font.size"] / 2
 
-            l1 = Line2D([x, x + w], [y + h, y], **lineparams)
-            l2 = Line2D([x, x + w], [y, y + h], **lineparams)
+        self.labels = [
+            ax.text(0.25, y, label, transform=ax.transAxes,
+                    horizontalalignment="left", verticalalignment="center")
+            for y, label in zip(ys, labels)]
 
-            l1.set_visible(active)
-            l2.set_visible(active)
-            self.labels.append(t)
-            self.rectangles.append(p)
-            self.lines.append((l1, l2))
-            ax.add_patch(p)
-            ax.add_line(l1)
-            ax.add_line(l2)
+        self._squares = ax.scatter(
+            [0.15] * len(ys), ys, marker='s', c="none", linewidth=1,
+            transform=ax.transAxes, edgecolor="k"
+        )
+        mask = [not x for x in actives]
+        self._crosses = ax.scatter(
+            [0.15] * len(ys), ys, marker='x', linewidth=1,
+            c=["k" if actives[i] else "none" for i in range(len(ys))],
+            transform=ax.transAxes
+        )
 
         self.connect_event('button_press_event', self._clicked)
 
@@ -1047,11 +1028,29 @@ def __init__(self, ax, labels, actives=None):
     def _clicked(self, event):
         if self.ignore(event) or event.button != 1 or event.inaxes != self.ax:
             return
-        for i, (p, t) in enumerate(zip(self.rectangles, self.labels)):
-            if (t.get_window_extent().contains(event.x, event.y) or
-                    p.get_window_extent().contains(event.x, event.y)):
-                self.set_active(i)
-                break
+        pclicked = self.ax.transAxes.inverted().transform((event.x, event.y))
+        _, square_inds = self._squares.contains(event)
+        coords = self._squares.get_offset_transform().transform(
+            self._squares.get_offsets()
+        )
+        distances = {}
+        if hasattr(self, "_rectangles"):
+            for i, (p, t) in enumerate(zip(self._rectangles, self.labels)):
+                if (t.get_window_extent().contains(event.x, event.y)
+                        or (
+                            p.get_x() < event.x < p.get_x() + p.get_width()
+                            and p.get_y() < event.y < p.get_y()
+                                                    + p.get_height()
+                            )):
+                    distances[i] = np.linalg.norm(pclicked - p.get_center())
+        else:
+            for i, t in enumerate(self.labels):
+                if (i in square_inds["ind"]
+                        or t.get_window_extent().contains(event.x, event.y)):
+                    distances[i] = np.linalg.norm(pclicked - coords[i])
+        if len(distances) > 0:
+            closest = min(distances, key=distances.get)
+            self.set_active(closest)
 
     def set_active(self, index):
         """
@@ -1072,9 +1071,18 @@ def set_active(self, index):
         if index not in range(len(self.labels)):
             raise ValueError(f'Invalid CheckButton index: {index}')
 
-        l1, l2 = self.lines[index]
-        l1.set_visible(not l1.get_visible())
-        l2.set_visible(not l2.get_visible())
+        if colors.same_color(
+                self._crosses.get_facecolor()[index], colors.to_rgba("none")
+        ):
+            self._crosses.get_facecolor()[index] = colors.to_rgba("k")
+        else:
+            self._crosses.get_facecolor()[index] = colors.to_rgba("none")
+
+        if hasattr(self, "_rectangles"):
+            for i, p in enumerate(self._rectangles):
+                p.set_facecolor("k" if colors.same_color(
+                    p.get_facecolor(), colors.to_rgba("none"))
+                                else "none")
 
         if self.drawon:
             self.ax.figure.canvas.draw()
@@ -1086,7 +1094,9 @@ def get_status(self):
         """
         Return a tuple of the status (True/False) of all of the check buttons.
         """
-        return [l1.get_visible() for (l1, l2) in self.lines]
+        return [False if colors.same_color(
+            self._crosses.get_facecolors()[i], colors.to_rgba("none"))
+                else True for i in range(len(self.labels))]
 
     def on_clicked(self, func):
         """
@@ -1100,6 +1110,24 @@ def disconnect(self, cid):
         """Remove the observer with connection id *cid*."""
         self._observers.disconnect(cid)
 
+    @property
+    def rectangles(self):
+        if not hasattr(self, "rectangles"):
+            dy = 1. / (len(self.labels) + 1)
+            w, h = dy / 2, dy / 2
+            rectangles = self._rectangles = [
+                Rectangle(xy=self._squares.get_offsets()[i], width=w, height=h,
+                          edgecolor="black",
+                          facecolor=self._squares.get_facecolor()[i],
+                          transform=self.ax.transAxes
+                          )
+                for i in range(len(self.labels))
+            ]
+            self._squares.set_visible(False)
+            for rectangle in rectangles:
+                self.ax.add_patch(rectangle)
+        return self._rectangles
+
 
 class TextBox(AxesWidget):
     """