X11: Fix no window position events during resize

A window resize action that also resulting in the window being moved did
not emit any window positions events, as the position of real
ConfigureNotify events was ignored.  The real events use parent
coordinates instead of root coordinates so this adds parent tracking and
conditional translation.

Fixes glfw#1613.

README.md

@@ -157,6 +157,7 @@ information on what to include when reporting a bug.
  - [X11] Bugfix: Changing `GLFW_FLOATING` on a hidden window could silently fail
  - [X11] Bugfix: Disabled cursor mode was interrupted by indicator windows
  - [X11] Bugfix: Monitor physical dimensions could be reported as zero mm
+ - [X11] Bugfix: Window position events were not emitted during resizing (#1613)
  - [Wayland] Removed support for `wl_shell` (#1443)
  - [Wayland] Bugfix: The `GLFW_HAND_CURSOR` shape used the wrong image (#1432)
  - [Wayland] Bugfix: `CLOCK_MONOTONIC` was not correctly enabled

src/x11_platform.h

@@ -186,6 +186,7 @@ typedef struct _GLFWwindowX11
 {
     Colormap        colormap;
     Window          handle;
+    Window          parent;
     XIC             ic;
 
     GLFWbool        overrideRedirect;

src/x11_window.c

@@ -1258,6 +1258,18 @@ static void processEvent(XEvent *event)
 
     switch (event->type)
     {
+        case CreateNotify:
+        {
+            window->x11.parent = event->xcreatewindow.parent;
+            return;
+        }
+
+        case ReparentNotify:
+        {
+            window->x11.parent = event->xreparent.parent;
+            return;
+        }
+
         case KeyPress:
         {
             const int key = translateKey(keycode);
@@ -1542,18 +1554,28 @@ static void processEvent(XEvent *event)
                 window->x11.height = event->xconfigure.height;
             }
 
-            if (event->xconfigure.x != window->x11.xpos ||
-                event->xconfigure.y != window->x11.ypos)
+            int xpos = event->xconfigure.x;
+            int ypos = event->xconfigure.y;
+
+            // NOTE: ConfigureNotify events from the server are in local
+            //       coordinates, so if we are reparented we need to translate
+            //       the position into root (screen) coordinates
+            if (!event->xany.send_event && window->x11.parent != _glfw.x11.root)
             {
-                if (window->x11.overrideRedirect || event->xany.send_event)
-                {
-                    _glfwInputWindowPos(window,
-                                        event->xconfigure.x,
-                                        event->xconfigure.y);
+                Window dummy;
+                XTranslateCoordinates(_glfw.x11.display,
+                                      window->x11.parent,
+                                      _glfw.x11.root,
+                                      xpos, ypos,
+                                      &xpos, &ypos,
+                                      &dummy);
+            }
 
-                    window->x11.xpos = event->xconfigure.x;
-                    window->x11.ypos = event->xconfigure.y;
-                }
+            if (xpos != window->x11.xpos || ypos != window->x11.ypos)
+            {
+                _glfwInputWindowPos(window, xpos, ypos);
+                window->x11.xpos = xpos;
+                window->x11.ypos = ypos;
             }
 
             return;