fix transforms for VLine and HLine

mpl_draggable_line/_line.py

@@ -6,6 +6,7 @@
 from matplotlib.backend_bases import MouseEvent
 from matplotlib.cbook import CallbackRegistry
 from matplotlib.lines import Line2D
+from matplotlib.transforms import IdentityTransform, blended_transform_factory
 from matplotlib.widgets import AxesWidget
 
 __all__ = [
@@ -16,7 +17,16 @@
 
 
 class DraggableLine(AxesWidget):
-    def __init__(self, ax, x, y, grab_range=10, useblit=False, **kwargs) -> None:
+    def __init__(
+        self,
+        ax,
+        x,
+        y,
+        grab_range=10,
+        useblit=False,
+        grab_range_transform=None,
+        **kwargs,
+    ) -> None:
         """
         Parameters
         ----------
@@ -29,6 +39,9 @@ def __init__(self, ax, x, y, grab_range=10, useblit=False, **kwargs) -> None:
             Whether to use blitting for faster drawing (if supported by the
             backend). See the tutorial :doc:`/tutorials/advanced/blitting`
             for details.
+        grab_range_transform : matplotlib.transform.Transform, optional
+            The transform to use for the handle positions when calculating
+            if a handle has been grabbed.
         **kwargs :
             Passed on to Line2D for styling
         """
@@ -43,6 +56,8 @@ def __init__(self, ax, x, y, grab_range=10, useblit=False, **kwargs) -> None:
         marker = kwargs.pop("marker", "o")
         color = kwargs.pop("color", "k")
         transform = kwargs.pop("transform", self.ax.transData)
+        self._grab_range_transform = grab_range_transform or self.ax.transLimits
+
         self._handles = Line2D(
             [x[0], center_x, x[1]],
             [y[0], center_y, y[1]],
@@ -108,12 +123,11 @@ def _on_press(self, event: MouseEvent):
         if not self.canvas.widgetlock.available(self):
             return
         # figure out if any handles are being grabbed
-        # maybe possible to do this with a pick event?
 
         x, y = self._handles.get_data()
-        # this is taken pretty much directly from the implementation
-        # in matplotlib.widget.ToolHandles.closest
-        pts = self.ax.transLimits.transform(np.column_stack([x, y]))
+        # this is a modified version of
+        # matplotlib.widget.ToolHandles.closest
+        pts = self._grab_range_transform.transform(np.column_stack([x, y]))
         diff = pts - self.ax.transLimits.transform((event.xdata, event.ydata))
         dist = np.hypot(*diff.T)
         idx = np.argmin(dist)
@@ -227,6 +241,9 @@ def __init__(self, ax, x, grab_range=0.1, useblit=False, **kwargs) -> None:
             grab_range=grab_range,
             useblit=useblit,
             transform=ax.get_xaxis_transform(),
+            grab_range_transform=blended_transform_factory(
+                ax.transLimits, IdentityTransform()
+            ),
             **kwargs,
         )
         self._y_lock = True
@@ -292,6 +309,9 @@ def __init__(self, ax, y, grab_range=0.1, useblit=False, **kwargs) -> None:
             grab_range=grab_range,
             useblit=useblit,
             transform=ax.get_yaxis_transform(),
+            grab_range_transform=blended_transform_factory(
+                IdentityTransform(), ax.transLimits
+            ),
             **kwargs,
         )
         self._x_lock = True