wm: Make WM_MOVE_PANEL use top-right coordinates.

src/platform/window_manager/wm_ipc.h

 // Copyright (c) 2009 The Chromium OS Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef WINDOW_MANAGER_WM_IPC_H_
 #define WINDOW_MANAGER_WM_IPC_H_
 
 #include <gdk/gdk.h>  // for GdkEventClient
 extern "C" {
 #include <X11/Xlib.h>
@@ skipping 74 matching lines @@
                      WindowType type,
                      const std::vector<int>* params);
 
   // Messages are sent via ClientMessageEvents that have 'message_type' set
   // to _CHROME_WM_MESSAGE, 'format' set to 32 (that is, 32-bit values),
   // and l[0] set to a value from the MessageType enum.  The remaining four
   // values in the 'l' array contain data specific to the type of message
   // being sent.
   struct Message {
    public:
+    // NOTE: Don't remove values from this enum; it is shared between
+    // Chrome and the window manager.
     enum Type {
       UNKNOWN = 0,
 
       // Notify Chrome when a floating tab has entered or left a tab
       // summary window.  Sent to the summary window.
       //   param[0]: X ID of the floating tab window
       //   param[1]: state (0 means left, 1 means entered or currently in)
       //   param[2]: X coordinate relative to summary window
       //   param[3]: Y coordinate
       CHROME_NOTIFY_FLOATING_TAB_OVER_TAB_SUMMARY,
@@ skipping 13 matching lines @@
       CHROME_SET_TAB_SUMMARY_VISIBILITY,
 
       // Tell the WM to collapse or expand a panel.
       //   param[0]: X ID of the panel window
       //   param[1]: desired state (0 means collapsed, 1 means expanded)
       WM_SET_PANEL_STATE,
 
       // Notify Chrome that the panel state has changed.  Sent to the panel
       // window.
       //   param[0]: new state (0 means collapsed, 1 means expanded)
-      // TODO: Get rid of this; Chrome can just watch for changes to the
+      // TODO: Deprecate this; Chrome can just watch for changes to the
       // _CHROME_STATE property to get the same information.
       CHROME_NOTIFY_PANEL_STATE,
 
       // Instruct the WM to move a floating tab.  The passed-in position is
       // that of the cursor; the tab's composited window is displaced based
       // on the cursor's offset from the upper-left corner of the tab at
       // the start of the drag.
       //   param[0]: X ID of the floating tab window
       //   param[1]: X coordinate to which the tab should be moved
       //   param[2]: Y coordinate
       WM_MOVE_FLOATING_TAB,
 
-      // Instruct the WM to move a panel.
-      //   param[0]: X ID of the panel window
-      //   param[1]: X coordinate to which the panel should be moved
-      //   param[2]: Y coordinate
-      WM_MOVE_PANEL,
+      // Notify the WM that a panel has been dragged.
+      //   param[0]: X ID of the panel's content window
+      //   param[1]: X coordinate to which the upper-right corner of the
+      //             panel's titlebar window was dragged
+      //   param[2]: Y coordinate to which the upper-right corner of the
+      //             panel's titlebar window was dragged
+      // Note: The point given is actually that of one pixel to the right
+      // of the upper-right corner of the titlebar window.  For example, a
+      // no-op move message for a 10-pixel wide titlebar whose upper-left
+      // point is at (0, 0) would contain the X and Y paremeters (10, 0):
+      // in other words, the position of the titlebar's upper-left point
+      // plus its width.  This is intended to make both the Chrome and WM
+      // side of things simpler and to avoid some easy-to-make off-by-one
+      // errors.
+      WM_NOTIFY_PANEL_DRAGGED,
 
       // Notify the WM that the panel drag is complete (that is, the mouse
       // button has been released).
-      //   param[0]: X ID of the panel window
+      //   param[0]: X ID of the panel's content window
       WM_NOTIFY_PANEL_DRAG_COMPLETE,
 
       // Instruct the WM to focus a window (either top-level or a panel).
       // This is used when a tab is clicked in a tab overview window, or
       // when the user clicks on a panel's titlebar to expand it.
       //   param[0]: X ID of the window to focus
       WM_FOCUS_WINDOW,
 
       // Notify Chrome that the layout mode (for example, overview or
       // focused) has changed.
       //   param[0]: new mode (0 means focused, 1 means overview)
       CHROME_NOTIFY_LAYOUT_MODE,
 
       // Instruct the WM to enter overview mode.
-      //   param[0]: X ID of the window show the tab overview for.
+      //   param[0]: X ID of the window to show the tab overview for.
       WM_SWITCH_TO_OVERVIEW_MODE,
 
+      // Let the WM know which version of this file Chrome is using.  It's
+      // difficult to make changes synchronously to Chrome and the WM (our
+      // build scripts can use a locally-built Chromium, the latest one
+      // from the buildbot, or an older hardcoded version), so it's useful
+      // to be able to maintain compatibility in the WM with versions of
+      // Chrome that exhibit older behavior.
+      //
+      // Chrome should send a message to the WM at startup containing the
+      // latest version from the list below.  For backwards compatibility,
+      // the WM assumes version 0 if it doesn't receive a message.  Here
+      // are the changes that have been made in successive versions of the
+      // protocol:
+      //
+      // 1: WM_NOTIFY_PANEL_DRAGGED contains the position of the
+      //    upper-right, rather than upper-left, corner of of the titlebar
+      //    window
+      //
+      // TODO: The latest version should be hardcoded in this file once the
+      // file is being shared between Chrome and the WM so Chrome can just
+      // pull it from there.  Better yet, the message could be sent
+      // automatically in WmIpc's c'tor.
+      //
+      //   param[0]: version of this protocol currently supported
+      WM_NOTIFY_IPC_VERSION,
+
       kNumTypes,
     };
 
     Message() {
       Init(UNKNOWN);
     }
     Message(Type type) {
       Init(type);
     }
 
@@ skipping 56 matching lines @@
 
   // Window used for sending messages to the window manager.
   XWindow wm_window_;
 
   DISALLOW_COPY_AND_ASSIGN(WmIpc);
 };
 
 }  // namespace window_manager
 
 #endif  // WINDOW_MANAGER_WM_IPC_H_