Merge pull request matplotlib#30543 from LangQi99/feat/zoom

ENH: support x/y-axis zoom

Author: QuLogic

doc/release/next_whats_new/scroll_to_zoom.rst

@@ -2,7 +2,8 @@ Zooming using mouse wheel
 ~~~~~~~~~~~~~~~~~~~~~~~~~
 
 ``Ctrl+MouseWheel`` can be used to zoom in the plot windows.
+Additionally, ``x+MouseWheel`` zooms only the x-axis and ``y+MouseWheel`` zooms only the y-axis.
 
-The zoom focusses on the mouse pointer, and keeps the aspect ratio of the axes.
+The zoom focusses on the mouse pointer. With ``Ctrl``, the axes aspect ratio is kept; with ``x`` or ``y``, only the respective axis is scaled.
 
 Zooming is currently only supported on rectilinear Axes.

lib/matplotlib/backend_bases.py

@@ -2592,7 +2592,7 @@ def scroll_handler(event, canvas=None, toolbar=None):
         # is required for interactive navigation.
         return
 
-    if event.key == "control":  # zoom towards the mouse position
+    if event.key in {"control", "x", "y"}:  # zoom towards the mouse position
         toolbar.push_current()
 
         xmin, xmax = ax.get_xlim()
@@ -2604,10 +2604,21 @@ def scroll_handler(event, canvas=None, toolbar=None):
         x, y = ax.transScale.transform((event.xdata, event.ydata))
 
         scale_factor = 0.85 ** event.step
-        new_xmin = x - (x - xmin) * scale_factor
-        new_xmax = x + (xmax - x) * scale_factor
-        new_ymin = y - (y - ymin) * scale_factor
-        new_ymax = y + (ymax - y) * scale_factor
+        # Determine which axes to scale based on key
+        zoom_x = event.key in {"control", "x"}
+        zoom_y = event.key in {"control", "y"}
+
+        if zoom_x:
+            new_xmin = x - (x - xmin) * scale_factor
+            new_xmax = x + (xmax - x) * scale_factor
+        else:
+            new_xmin, new_xmax = xmin, xmax
+
+        if zoom_y:
+            new_ymin = y - (y - ymin) * scale_factor
+            new_ymax = y + (ymax - y) * scale_factor
+        else:
+            new_ymin, new_ymax = ymin, ymax
 
         inv_scale = ax.transScale.inverted()
         (new_xmin, new_ymin), (new_xmax, new_ymax) = inv_scale.transform(