Box zoom keeps existing aspect ratios

scottshambaugh · scottshambaugh · commit 0008c02b9264 · 2022-08-27T13:41:25.000-06:00
diff --git a/doc/users/next_whats_new/3d_plot_pan_zoom.rst b/doc/users/next_whats_new/3d_plot_pan_zoom.rst
@@ -4,4 +4,5 @@
 The pan and zoom buttons in the toolbar of 3D plots are now enabled.
 Deselect both to rotate the plot. When the zoom button is pressed,
 zoom in by using the left mouse button to draw a bounding box, and
-out by using the right mouse button to draw the box.
+out by using the right mouse button to draw the box. When zooming a
+3D plot, the current view aspect ratios are kept fixed.
diff --git a/lib/mpl_toolkits/mplot3d/axes3d.py b/lib/mpl_toolkits/mplot3d/axes3d.py
@@ -1213,19 +1213,21 @@ def _set_view_from_bbox(self, bbox, direction='in',
         dy = abs(start_y - stop_y)
         scale_u = dx / (self.bbox.max[0] - self.bbox.min[0])
         scale_v = dy / (self.bbox.max[1] - self.bbox.min[1])
-        scale_w = max(scale_u, scale_v)
 
         # Limit box zoom to reasonable range, protect for divide by zero below
-        scale_u = np.clip(scale_u, 1e-2, 1e2)
-        scale_v = np.clip(scale_v, 1e-2, 1e2)
+        scale_u = np.clip(scale_u, 1e-2, 1)
+        scale_v = np.clip(scale_v, 1e-2, 1)
 
+        # Keep aspect ratios equal
+        scale = max(scale_u, scale_v)
+
+        # Zoom out
         if direction == 'out':
-            scale_u = 1 / scale_u
-            scale_v = 1 / scale_v
+            scale = 1 / scale
 
-        self._zoom_data_limits(scale_u, scale_v, scale_w)
+        self.zoom_data_limits(scale, scale, scale)
 
-    def _zoom_data_limits(self, scale_u, scale_v, scale_w):
+    def zoom_data_limits(self, scale_u, scale_v, scale_w):
         """
         Zoom in or out of a 3D plot.
         Will scale the data limits by the scale factors, where scale_u,
@@ -1237,19 +1239,23 @@ def _zoom_data_limits(self, scale_u, scale_v, scale_w):
         'equalyz', or 'equalxz', the relevant axes are constrained to zoom
         equally.
         """
-        # Convert from the scale factors in the view frame to the data frame
-        R = np.array([self._view_u, self._view_v, self._view_w])
-        S = np.array([scale_u, scale_v, scale_w]) * np.eye(3)
-        scale = np.linalg.norm(R.T @ S, axis=1)
+        scale = np.array([scale_u, scale_v, scale_w])
+
+        # Only perform frame conversion if unequal scale factors
+        if not np.allclose(scale, scale_u):
+            # Convert from the scale factors in the view frame to the data frame
+            R = np.array([self._view_u, self._view_v, self._view_w])
+            S = scale * np.eye(3)
+            scale = np.linalg.norm(R.T @ S, axis=1)
 
-        # Set the constrained scale factors to the factor closest to 1
-        if self._aspect in ('equal', 'equalxy', 'equalxz', 'equalyz'):
-            ax_idx = self._equal_aspect_axis_indices(self._aspect)
-            scale[ax_idx] = scale[ax_idx][np.argmin(np.abs(scale[ax_idx] - 1))]
+            # Set the constrained scale factors to the factor closest to 1
+            if self._aspect in ('equal', 'equalxy', 'equalxz', 'equalyz'):
+                ax_idx = self._equal_aspect_axis_indices(self._aspect)
+                scale[ax_idx] = scale[ax_idx][np.argmin(np.abs(scale[ax_idx] - 1))]
 
-        self._scale_axis_limits(scale[0], scale[1], scale[2])
+        self.scale_axis_limits(scale[0], scale[1], scale[2])
 
-    def _scale_axis_limits(self, scale_x, scale_y, scale_z):
+    def scale_axis_limits(self, scale_x, scale_y, scale_z):
         """
         Keeping the center of the x, y, and z data axes fixed, scale their
         limits by scale factors. A scale factor > 1 zooms out and a scale
diff --git a/lib/mpl_toolkits/tests/test_mplot3d.py b/lib/mpl_toolkits/tests/test_mplot3d.py
@@ -1622,13 +1622,13 @@ def convert_lim(dmin, dmax):
 
 @pytest.mark.parametrize("tool,button,key,expected",
                          [("zoom", MouseButton.LEFT, None,  # zoom in
-                          ((0.03, 0.61), (0.27, 0.71), (0.32, 0.89))),
+                          ((0.26, 0.38), (0.43, 0.55), (0.54, 0.66))),
                           ("zoom", MouseButton.LEFT, 'x',  # zoom in
-                          ((0.17, 0.73), (0.09, 0.43), (-0.06, 0.06))),
+                          ((0.39, 0.51), (0.20, 0.32), (-0.06, 0.06))),
                           ("zoom", MouseButton.LEFT, 'y',  # zoom in
-                          ((-0.23, -0.03), (0.07, 0.37), (0.32, 0.89))),
+                          ((-0.19, -0.07), (0.16, 0.28), (0.54, 0.66))),
                           ("zoom", MouseButton.RIGHT, None,  # zoom out
-                          ((0.29, 0.35), (0.44, 0.53), (0.57, 0.64))),
+                          ((0.26, 0.38), (0.43, 0.55), (0.54, 0.66))),
                           ("pan", MouseButton.LEFT, None,
                           ((-0.70, -0.58), (-1.03, -0.91), (-1.27, -1.15))),
                           ("pan", MouseButton.LEFT, 'x',
