Added direct graph navigation without activating Matplotlib toolbar modes:

Mouse wheel zooms in and out around the cursor.
Left-click dragging pans the graph.
Matplotlib toolbar modes still work and take precedence when activated.
The existing Home button can reset the view.

BEdit/src/bedit/gui/simulation_window.py

@@ -1,6 +1,7 @@
 import re
 from pathlib import Path
 
+from matplotlib.backend_bases import MouseButton
 from matplotlib.backends.backend_qtagg import FigureCanvasQTAgg, NavigationToolbar2QT
 from matplotlib.figure import Figure
 from PySide6.QtCore import Qt, Signal
@@ -550,9 +551,11 @@ class GraphWorkspacePage(QWidget):
         self.results = results
         self.plot_layout = QVBoxLayout(self)
         self.figure = Figure(layout="constrained")
-        self.canvas = FigureCanvasQTAgg(self.figure)
+        self.canvas = InteractiveFigureCanvas(self.figure)
         self.axes = self.figure.add_subplot(111)
-        self.navigation_toolbar = NavigationToolbar2QT(self.canvas, self)
+        self.canvas.axes = self.axes
+        self.navigation_toolbar = GraphNavigationToolbar(self.canvas, self)
+        self.canvas.navigation_toolbar = self.navigation_toolbar
         self.plot_layout.addWidget(self.navigation_toolbar)
         self.plot_layout.addWidget(self.canvas)
         self.refresh_chart()
@@ -578,9 +581,110 @@ class GraphWorkspacePage(QWidget):
         self.axes.grid(True, alpha=0.25)
         if self.axes.lines:
             self.axes.legend()
+        self.axes.relim()
+        self.axes.autoscale_view()
+        self.canvas.set_home_view()
         self.canvas.draw_idle()
 
 
+class GraphNavigationToolbar(NavigationToolbar2QT):
+    """Navigation toolbar whose Home action includes direct canvas navigation."""
+
+    def home(self, *args) -> None:
+        del args
+        self.canvas.reset_home_view()
+
+
+class InteractiveFigureCanvas(FigureCanvasQTAgg):
+    """Matplotlib canvas with always-available wheel zoom and drag pan."""
+
+    def __init__(self, figure: Figure) -> None:
+        super().__init__(figure)
+        self.axes = None
+        self.navigation_toolbar = None
+        self._pan_start = None
+        self._home_view = None
+        self.mpl_connect("scroll_event", self._zoom_at_cursor)
+        self.mpl_connect("button_press_event", self._start_pan)
+        self.mpl_connect("motion_notify_event", self._pan)
+        self.mpl_connect("button_release_event", self._finish_pan)
+
+    def _toolbar_is_active(self) -> bool:
+        return bool(
+            self.navigation_toolbar is not None
+            and self.navigation_toolbar.mode
+        )
+
+    def set_home_view(self) -> None:
+        if self.axes is not None:
+            self._home_view = (self.axes.get_xlim(), self.axes.get_ylim())
+
+    def reset_home_view(self) -> None:
+        if self.axes is None or self._home_view is None:
+            return
+        x_limits, y_limits = self._home_view
+        self.axes.set_xlim(x_limits)
+        self.axes.set_ylim(y_limits)
+        self.draw_idle()
+
+    def _zoom_at_cursor(self, event) -> None:
+        if (
+            self.axes is None
+            or event.inaxes is not self.axes
+            or event.xdata is None
+            or event.ydata is None
+            or self._toolbar_is_active()
+        ):
+            return
+        scale = 0.8 if event.button == "up" else 1.25
+        left, right = self.axes.get_xlim()
+        bottom, top = self.axes.get_ylim()
+        self.axes.set_xlim(
+            event.xdata - (event.xdata - left) * scale,
+            event.xdata + (right - event.xdata) * scale,
+        )
+        self.axes.set_ylim(
+            event.ydata - (event.ydata - bottom) * scale,
+            event.ydata + (top - event.ydata) * scale,
+        )
+        self.draw_idle()
+
+    def _start_pan(self, event) -> None:
+        if (
+            self.axes is None
+            or event.inaxes is not self.axes
+            or event.button != MouseButton.LEFT
+            or self._toolbar_is_active()
+        ):
+            return
+        self._pan_start = (
+            event.x,
+            event.y,
+            self.axes.get_xlim(),
+            self.axes.get_ylim(),
+        )
+
+    def _pan(self, event) -> None:
+        if (
+            self.axes is None
+            or self._pan_start is None
+            or event.x is None
+            or event.y is None
+        ):
+            return
+        start_x, start_y, x_limits, y_limits = self._pan_start
+        width = max(self.axes.bbox.width, 1.0)
+        height = max(self.axes.bbox.height, 1.0)
+        delta_x = (event.x - start_x) * (x_limits[1] - x_limits[0]) / width
+        delta_y = (event.y - start_y) * (y_limits[1] - y_limits[0]) / height
+        self.axes.set_xlim(x_limits[0] - delta_x, x_limits[1] - delta_x)
+        self.axes.set_ylim(y_limits[0] - delta_y, y_limits[1] - delta_y)
+        self.draw_idle()
+
+    def _finish_pan(self, _event) -> None:
+        self._pan_start = None
+
+
 def _safe_file_stem(model_name: str) -> str:
     stem = re.sub(r"[^A-Za-z0-9_.-]+", "_", model_name).strip("._")
     return stem or "simulation"