When setting an X11 icon fails, try halving the size

When setting an icon that is too large previously Godot would die with a
X Error of failed request:  BadLength error. To avoid this we install an
error handler right before we set an icon. If the error handler triggers
we halve the icon size until it works or until we've reached a 0 size on
either width or height.

We print a warning when this happens to alert developers.

This fixes #19716

platform/x11/os_x11.cpp

@@ -2628,41 +2628,82 @@ void OS_X11::alert(const String &p_alert, const String &p_title) {
 	return;
 }
 
+bool g_set_icon_error = false;
+int set_icon_errorhandler(Display *dpy, XErrorEvent *ev) {
+	g_set_icon_error = true;
+	return 0;
+}
+
 void OS_X11::set_icon(const Ref<Image> &p_icon) {
+	int (*oldHandler)(Display *, XErrorEvent *) = XSetErrorHandler(&set_icon_errorhandler);
+
 	Atom net_wm_icon = XInternAtom(x11_display, "_NET_WM_ICON", False);
 
 	if (p_icon.is_valid()) {
 		Ref<Image> img = p_icon->duplicate();
 		img->convert(Image::FORMAT_RGBA8);
 
-		int w = img->get_width();
-		int h = img->get_height();
+		while (true) {
+			int w = img->get_width();
+			int h = img->get_height();
 
-		// We're using long to have wordsize (32Bit build -> 32 Bits, 64 Bit build -> 64 Bits
-		Vector<long> pd;
+			if (g_set_icon_error) {
+				g_set_icon_error = false;
 
-		pd.resize(2 + w * h);
+				WARN_PRINT("Icon too large, attempting to resize icon.");
 
-		pd.write[0] = w;
-		pd.write[1] = h;
+				int new_width, new_height;
+				if (w > h) {
+					new_width = w / 2;
+					new_height = h * new_width / w;
+				} else {
+					new_height = h / 2;
+					new_width = w * new_height / h;
+				}
 
-		PoolVector<uint8_t>::Read r = img->get_data().read();
+				w = new_width;
+				h = new_height;
 
-		long *wr = &pd.write[2];
-		uint8_t const *pr = r.ptr();
+				if (!w || !h) {
+					WARN_PRINT("Unable to set icon.");
+					break;
+				}
+
+				img->resize(w, h, Image::INTERPOLATE_CUBIC);
+			}
 
-		for (int i = 0; i < w * h; i++) {
-			long v = 0;
-			//    A             R             G            B
-			v |= pr[3] << 24 | pr[0] << 16 | pr[1] << 8 | pr[2];
-			*wr++ = v;
-			pr += 4;
+			// We're using long to have wordsize (32Bit build -> 32 Bits, 64 Bit build -> 64 Bits
+			Vector<long> pd;
+
+			pd.resize(2 + w * h);
+
+			pd.write[0] = w;
+			pd.write[1] = h;
+
+			PoolVector<uint8_t>::Read r = img->get_data().read();
+
+			long *wr = &pd.write[2];
+			uint8_t const *pr = r.ptr();
+
+			for (int i = 0; i < w * h; i++) {
+				long v = 0;
+				//    A             R             G            B
+				v |= pr[3] << 24 | pr[0] << 16 | pr[1] << 8 | pr[2];
+				*wr++ = v;
+				pr += 4;
+			}
+
+			XChangeProperty(x11_display, x11_window, net_wm_icon, XA_CARDINAL, 32, PropModeReplace, (unsigned char *)pd.ptr(), pd.size());
+
+			if (!g_set_icon_error)
+				break;
 		}
-		XChangeProperty(x11_display, x11_window, net_wm_icon, XA_CARDINAL, 32, PropModeReplace, (unsigned char *)pd.ptr(), pd.size());
 	} else {
 		XDeleteProperty(x11_display, x11_window, net_wm_icon);
 	}
+
 	XFlush(x11_display);
+	XSetErrorHandler(oldHandler);
 }
 
 void OS_X11::force_process_input() {