Merge pull request matplotlib#22163 from daniilS/tk_toolbar_colours

Change colour of Tk toolbar icons on dark backgrounds

Author: tacaswell

lib/matplotlib/backends/_backend_tk.py

@@ -637,12 +637,63 @@ def _set_image_for_button(self, button):
         path_large = path_regular.with_name(
             path_regular.name.replace('.png', '_large.png'))
         size = button.winfo_pixels('18p')
+
+        # Nested functions because ToolbarTk calls  _Button.
+        def _get_color(color_name):
+            # `winfo_rgb` returns an (r, g, b) tuple in the range 0-65535
+            return button.winfo_rgb(button.cget(color_name))
+
+        def _is_dark(color):
+            if isinstance(color, str):
+                color = _get_color(color)
+            return max(color) < 65535 / 2
+
+        def _recolor_icon(image, color):
+            image_data = np.asarray(image).copy()
+            black_mask = (image_data[..., :3] == 0).all(axis=-1)
+            image_data[black_mask, :3] = color
+            return Image.fromarray(image_data, mode="RGBA")
+
         # Use the high-resolution (48x48 px) icon if it exists and is needed
         with Image.open(path_large if (size > 24 and path_large.exists())
                         else path_regular) as im:
             image = ImageTk.PhotoImage(im.resize((size, size)), master=self)
-        button.configure(image=image, height='18p', width='18p')
-        button._ntimage = image  # Prevent garbage collection.
+            button._ntimage = image
+
+            # create a version of the icon with the button's text color
+            foreground = (255 / 65535) * np.array(
+                button.winfo_rgb(button.cget("foreground")))
+            im_alt = _recolor_icon(im, foreground)
+            image_alt = ImageTk.PhotoImage(
+                im_alt.resize((size, size)), master=self)
+            button._ntimage_alt = image_alt
+
+        if _is_dark("background"):
+            button.configure(image=image_alt)
+        else:
+            button.configure(image=image)
+        # Checkbuttons may switch the background to `selectcolor` in the
+        # checked state, so check separately which image it needs to use in
+        # that state to still ensure enough contrast with the background.
+        if (
+            isinstance(button, tk.Checkbutton)
+            and button.cget("selectcolor") != ""
+        ):
+            if self._windowingsystem != "x11":
+                selectcolor = "selectcolor"
+            else:
+                # On X11, selectcolor isn't used directly for indicator-less
+                # buttons. See `::tk::CheckEnter` in the Tk button.tcl source
+                # code for details.
+                r1, g1, b1 = _get_color("selectcolor")
+                r2, g2, b2 = _get_color("activebackground")
+                selectcolor = ((r1+r2)/2, (g1+g2)/2, (b1+b2)/2)
+            if _is_dark(selectcolor):
+                button.configure(selectimage=image_alt)
+            else:
+                button.configure(selectimage=image)
+
+        button.configure(height='18p', width='18p')
 
     def _Button(self, text, image_file, toggle, command):
         if not toggle:

lib/matplotlib/tests/test_backend_tk.py

@@ -216,3 +216,41 @@ def check_focus():
 
     if success:
         print("success")
+
+
+@_isolated_tk_test(success_count=2)
+def test_embedding():
+    import tkinter as tk
+    from matplotlib.backends.backend_tkagg import (
+        FigureCanvasTkAgg, NavigationToolbar2Tk)
+    from matplotlib.backend_bases import key_press_handler
+    from matplotlib.figure import Figure
+
+    root = tk.Tk()
+
+    def test_figure(master):
+        fig = Figure()
+        ax = fig.add_subplot()
+        ax.plot([1, 2, 3])
+
+        canvas = FigureCanvasTkAgg(fig, master=master)
+        canvas.draw()
+        canvas.mpl_connect("key_press_event", key_press_handler)
+        canvas.get_tk_widget().pack(expand=True, fill="both")
+
+        toolbar = NavigationToolbar2Tk(canvas, master, pack_toolbar=False)
+        toolbar.pack(expand=True, fill="x")
+
+        canvas.get_tk_widget().forget()
+        toolbar.forget()
+
+    test_figure(root)
+    print("success")
+
+    # Test with a dark button color. Doesn't actually check whether the icon
+    # color becomes lighter, just that the code doesn't break.
+
+    root.tk_setPalette(background="sky blue", selectColor="midnight blue",
+                       foreground="white")
+    test_figure(root)
+    print("success")