Backport PR matplotlib#32038: Fix occasional misalignment in reported mouse position (also fixes a bug with canvas height)

Author: QuLogic

lib/matplotlib/backend_bases.py

@@ -2059,8 +2059,16 @@ def get_width_height(self, *, physical=False):
         width, height : int
             The size of the figure, in points or pixels, depending on the
             backend.
+
+        Notes
+        -----
+        This method normally truncates the height/width to remove any fractional pixel.
+        However, if the height/width is extremely close to the integer pixel (within
+        1e-8 pixel), the height/width is instead rounded up to account for
+        floating-point precision effects.
         """
-        return tuple(int(size / (1 if physical else self.device_pixel_ratio))
+        # The tolerance of 1e-8 covers a floating-point tick for even 100,000 pixels
+        return tuple(int(size / (1 if physical else self.device_pixel_ratio) + 1e-8)
                      for size in self.figure.bbox.max)
 
     @classmethod

lib/matplotlib/backends/_backend_gtk.py

@@ -275,7 +275,7 @@ def set_message(self, s):
         self.message.set_markup(f'<small>{escaped}</small>')
 
     def draw_rubberband(self, event, x0, y0, x1, y1):
-        height = self.canvas.figure.bbox.height
+        height = self.canvas.get_width_height(physical=True)[1]
         y1 = height - y1
         y0 = height - y0
         rect = [int(val) for val in (x0, y0, x1 - x0, y1 - y0)]

lib/matplotlib/backends/_backend_tk.py

@@ -327,9 +327,10 @@ def get_tk_widget(self):
     def _event_mpl_coords(self, event):
         # calling canvasx/canvasy allows taking scrollbars into account (i.e.
         # the top of the widget may have been scrolled out of view).
+        height = self.get_width_height(physical=True)[1]
         return (self._tkcanvas.canvasx(event.x),
                 # flipy so y=0 is bottom of canvas
-                self.figure.bbox.height - self._tkcanvas.canvasy(event.y))
+                height - self._tkcanvas.canvasy(event.y))
 
     def motion_notify_event(self, event):
         MouseEvent("motion_notify_event", self,
@@ -389,7 +390,7 @@ def scroll_event_windows(self, event):
         if w != self._tkcanvas:
             return
         x = self._tkcanvas.canvasx(event.x_root - w.winfo_rootx())
-        y = (self.figure.bbox.height
+        y = (self.get_width_height(physical=True)[1]
              - self._tkcanvas.canvasy(event.y_root - w.winfo_rooty()))
         step = event.delta / 120
         MouseEvent("scroll_event", self,
@@ -676,7 +677,7 @@ def __init__(self, canvas, window=None, *, pack_toolbar=True):
         if window is None:
             window = canvas.get_tk_widget().master
         tk.Frame.__init__(self, master=window, borderwidth=2,
-                          width=int(canvas.figure.bbox.width), height=50)
+                          width=canvas.get_width_height()[0], height=50)
         # Avoid message_label expanding the toolbar size, and in turn expanding the
         # canvas size.
         # Without pack_propagate(False), when the user defines a small figure size
@@ -774,7 +775,7 @@ def draw_rubberband(self, event, x0, y0, x1, y1):
             self.canvas._tkcanvas.delete(self.canvas._rubberband_rect_white)
         if self.canvas._rubberband_rect_black:
             self.canvas._tkcanvas.delete(self.canvas._rubberband_rect_black)
-        height = self.canvas.figure.bbox.height
+        height = self.canvas.get_width_height(physical=True)[1]
         y0 = height - y0
         y1 = height - y1
         self.canvas._rubberband_rect_black = (

lib/matplotlib/backends/backend_agg.py

@@ -441,7 +441,7 @@ def draw(self):
             super().draw()
 
     def get_renderer(self):
-        w, h = self.figure.bbox.size
+        w, h = self.get_width_height(physical=True)
         key = w, h, self.figure.dpi
         reuse_renderer = (self._lastKey == key)
         if not reuse_renderer:

lib/matplotlib/backends/backend_gtk3.py

@@ -119,7 +119,7 @@ def _mpl_coords(self, event=None):
             x, y = event.x, event.y
         x = x * self.device_pixel_ratio
         # flip y so y=0 is bottom of canvas
-        y = self.figure.bbox.height - y * self.device_pixel_ratio
+        y = self.get_width_height(physical=True)[1] - y * self.device_pixel_ratio
         return x, y
 
     def scroll_event(self, widget, event):

lib/matplotlib/backends/backend_gtk4.py

@@ -117,7 +117,7 @@ def _mpl_coords(self, xy=None):
             x, y = xy
         x = x * self.device_pixel_ratio
         # flip y so y=0 is bottom of canvas
-        y = self.figure.bbox.height - y * self.device_pixel_ratio
+        y = self.get_width_height(physical=True)[1] - y * self.device_pixel_ratio
         return x, y
 
     def scroll_event(self, controller, dx, dy):

lib/matplotlib/backends/backend_qt.py

@@ -302,7 +302,7 @@ def mouseEventCoords(self, pos=None):
         # (otherwise, it's already a QPoint)
         x = pos.x()
         # flip y so y=0 is bottom of canvas
-        y = self.figure.bbox.height / self.device_pixel_ratio - pos.y()
+        y = self.get_width_height()[1] - pos.y()
         return x * self.device_pixel_ratio, y * self.device_pixel_ratio
 
     def enterEvent(self, event):
@@ -915,7 +915,7 @@ def set_message(self, s):
             self.locLabel.setText(s)
 
     def draw_rubberband(self, event, x0, y0, x1, y1):
-        height = self.canvas.figure.bbox.height
+        height = self.canvas.get_width_height(physical=True)[1]
         y1 = height - y1
         y0 = height - y0
         rect = [int(val) for val in (x0, y0, x1 - x0, y1 - y0)]

lib/matplotlib/backends/backend_tkcairo.py

@@ -9,8 +9,7 @@
 
 class FigureCanvasTkCairo(FigureCanvasCairo, FigureCanvasTk):
     def draw(self):
-        width = int(self.figure.bbox.width)
-        height = int(self.figure.bbox.height)
+        width, height = self.get_width_height(physical=True)
         surface = cairo.ImageSurface(cairo.FORMAT_ARGB32, width, height)
         self._renderer.set_context(cairo.Context(surface))
         self._renderer.dpi = self.figure.dpi

lib/matplotlib/backends/backend_webagg_core.py

@@ -492,7 +492,7 @@ def add_web_socket(self, web_socket):
         assert hasattr(web_socket, 'send_binary')
         assert hasattr(web_socket, 'send_json')
         self.web_sockets.add(web_socket)
-        self.resize(*self.canvas.figure.bbox.size)
+        self.resize(*self.canvas.get_width_height(physical=True))
         self._send_event('refresh')
 
     def remove_web_socket(self, web_socket):

lib/matplotlib/backends/backend_wx.py

@@ -746,9 +746,9 @@ def _mpl_coords(self, pos=None):
         # flip y so y=0 is bottom of canvas
         if not wx.Platform == '__WXMSW__':
             scale = self.GetDPIScaleFactor()
-            return x*scale, self.figure.bbox.height - y*scale
+            return x*scale, self.get_width_height(physical=True)[1] - y*scale
         else:
-            return x, self.figure.bbox.height - y
+            return x, self.get_width_height(physical=True)[1] - y
 
     def _on_key_down(self, event):
         """Capture key press."""
@@ -1169,7 +1169,7 @@ def save_figure(self, *args):
                 dialog.Destroy()
 
     def draw_rubberband(self, event, x0, y0, x1, y1):
-        height = self.canvas.figure.bbox.height
+        height = self.canvas.get_width_height(physical=True)[1]
         sf = 1 if wx.Platform == '__WXMSW__' else self.canvas.GetDPIScaleFactor()
         self.canvas._rubberband_rect = (x0/sf, (height - y0)/sf,
                                         x1/sf, (height - y1)/sf)