Change colour of Tk toolbar icons on dark backgrounds

daniilS · timhoffm · daniilS · commit 3f88047fb6ce · 2022-01-09T22:15:18.000Z
Co-Authored-By: Tim Hoffmann &lt;2836374+timhoffm@users.noreply.github.com&gt;
diff --git a/lib/matplotlib/backends/_backend_tk.py b/lib/matplotlib/backends/_backend_tk.py
@@ -652,6 +652,24 @@ def _set_image_for_button(self, button):
         # 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:
+            colors = ["background", "activebackground"]
+            if isinstance(button, tk.Checkbutton):
+                colors.append("selectcolor")
+            for color in colors:
+                if button.cget(color) == "":
+                    continue
+                # Get the color as an (r, g, b) tuple in the range from 0 to
+                # 65535, and check if its HSV V is under 50%.
+                if max(button.winfo_rgb(button.cget(color))) < 65535 / 2:
+                    # Change the colour of the icon to be visible against
+                    # the dark background.
+                    foreground = (255 / 65535) * np.array(
+                        button.winfo_rgb(button.cget("foreground")))
+                    image_data = np.asarray(im).copy()
+                    black_mask = (image_data[..., :3] == 0).all(axis=-1)
+                    image_data[black_mask, :3] = foreground
+                    im = Image.fromarray(image_data, mode="RGBA")
+                    break
             image = ImageTk.PhotoImage(im.resize((size, size)), master=self)
         button.configure(image=image, height='18p', width='18p')
         button._ntimage = image  # Prevent garbage collection.
diff --git a/lib/matplotlib/tests/test_backend_tk.py b/lib/matplotlib/tests/test_backend_tk.py
@@ -185,3 +185,42 @@ class Toolbar(NavigationToolbar2Tk):
     print("success")
     Toolbar(fig.canvas, fig.canvas.manager.window)  # This should not raise.
     print("success")
+
+
+@pytest.mark.backend('TkAgg', skip_on_importerror=True)
+@_isolated_tk_test(success_count=2)
+def test_embedding():  # pragma: no cover
+    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")
