Add XSECURELOCK_AUTH_Y_POSITION env var for vertical dialog placement

Allow configuring the vertical position of the auth dialog as a
percentage (0=top, 50=center, 100=bottom), defaulting to 50 (centered)
to preserve existing behavior.

Author: Radosław Stachowiak

README.md

@@ -253,6 +253,10 @@ Options to XSecureLock can be passed by environment variables:
     the screen saver.
 *   `XSECURELOCK_AUTH_WARNING_COLOR`: specifies the X11 color (see manpage of
     XParseColor) for the warning text of the auth dialog.
+*   `XSECURELOCK_AUTH_Y_POSITION`: vertical position of the auth dialog as a
+    percentage of screen height, from 0 (top) to 100 (bottom). Defaults to 50
+    (vertically centered). For example, set to 80 to position the dialog near
+    the bottom of the screen.
 *   `XSECURELOCK_BACKGROUND_COLOR`: specifies the X11 color (see manpage
     of XParseColor) for the background of the main and saver windows.
 *   `XSECURELOCK_BLANK_TIMEOUT`: specifies the time (in seconds) before telling

helpers/auth_x11.c

@@ -245,6 +245,10 @@ static int auth_sounds = 0;
 //! Whether to blink the cursor in the auth dialog.
 static int auth_cursor_blink = 1;
 
+//! Vertical position of the auth dialog as a percentage (0=top, 50=center,
+//! 100=bottom).
+static int auth_y_position = 50;
+
 //! Whether we only want a single auth window.
 static int single_auth_window = 0;
 
@@ -570,7 +574,7 @@ void CreateOrUpdatePerMonitorWindow(size_t i, const Monitor *monitor,
   int w = region_w;
   int h = region_h;
   int x = monitor->x + (monitor->width - w) / 2 + x_offset;
-  int y = monitor->y + (monitor->height - h) / 2 + y_offset;
+  int y = monitor->y + (monitor->height - h) * auth_y_position / 100 + y_offset;
   // Clip to monitor.
   if (x < 0) {
     w += x;
@@ -1620,6 +1624,9 @@ int main(int argc_local, char **argv_local) {
   auth_sounds = GetIntSetting("XSECURELOCK_AUTH_SOUNDS", 0);
   single_auth_window = GetIntSetting("XSECURELOCK_SINGLE_AUTH_WINDOW", 0);
   auth_cursor_blink = GetIntSetting("XSECURELOCK_AUTH_CURSOR_BLINK", 1);
+  auth_y_position = GetIntSetting("XSECURELOCK_AUTH_Y_POSITION", 50);
+  if (auth_y_position < 0) auth_y_position = 0;
+  if (auth_y_position > 100) auth_y_position = 100;
 #ifdef HAVE_XKB_EXT
   show_keyboard_layout =
       GetIntSetting("XSECURELOCK_SHOW_KEYBOARD_LAYOUT", 1);