dix: lookup function for WindowPtr by XID

This new lookup function retrieves a pointer to WindowRec structure by
associated XID. Unlike dixLookupWindow(), this one works globally, instead
of just on one specific client, and it doesn't do any XACE calls.

Signed-off-by: Enrico Weigelt, metux IT consult <info@metux.net>

dix/dix_priv.h

@@ -253,4 +253,15 @@ extern Bool explicit_display;
 extern Bool disableBackingStore;
 extern Bool enableBackingStore;
 
+/*
+ * @brief lookup window by XID
+ *
+ * This globally looks for Window with given XID (all screens, all clients)
+ * and returns a pointer to it. If not found, returns NULL.
+ *
+ * Unlike ::dixLookupWindow() it doesn't scan only one given client, nor does
+ * it do any XACE calls.
+ */
+WindowPtr dixLookupWindowByXID(Window window);
+
 #endif /* _XSERVER_DIX_PRIV_H */

dix/lookup.c

@@ -0,0 +1,42 @@
+/* SPDX-License-Identifier: MIT OR X11
+ *
+ * Copyright © 2024 Enrico Weigelt, metux IT consult <info@metux.net>
+ *
+ * @brief DIX lookup functions
+ */
+#include <dix-config.h>
+
+#include "dix/dix_priv.h"
+#include "include/windowstr.h"
+
+struct window_xid_match {
+    WindowPtr pWin;
+    Window id;
+};
+
+static int dix_match_window_xid(WindowPtr pWin, void *ptr)
+{
+    struct window_xid_match *walk = (struct window_xid_match*) ptr;
+
+    if (walk->id == pWin->drawable.id) {
+        walk->pWin = pWin;
+        return WT_STOPWALKING;
+    }
+    else
+        return WT_WALKCHILDREN;
+}
+
+WindowPtr dixLookupWindowByXID(Window window)
+{
+    struct window_xid_match walk = {
+        .id = window,
+    };
+
+    for (int i = 0; i < screenInfo.numScreens; i++) {
+        WalkTree(screenInfo.screens[i], dix_match_window_xid, &walk);
+        if (walk.pWin)
+            break;
+    }
+
+    return walk.pWin;
+}

dix/meson.build

@@ -19,6 +19,7 @@ srcs_dix = [
     'glyphcurs.c',
     'grabs.c',
     'inpututils.c',
+    'lookup.c',
     'pixmap.c',
     'privates.c',
     'property.c',