moving from https://github.com/perberos/mate-desktop-environment

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diff --git a/src/core/stack.h b/src/core/stack.h
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+/* -*- mode: C; c-file-style: "gnu"; indent-tabs-mode: nil; -*- */
+
+/**
+ * \file stack.h  Which windows cover which other windows
+ *
+ * There are two factors that determine window position.
+ * 
+ * One is window->stack_position, which is a unique integer
+ * indicating how windows are ordered with respect to one
+ * another. The ordering here transcends layers; it isn't changed
+ * as the window is moved among layers. This allows us to move several
+ * windows from one layer to another, while preserving the relative
+ * order of the moved windows. Also, it allows us to restore
+ * the stacking order from a saved session.
+ * 
+ * However when actually stacking windows on the screen, the
+ * layer overrides the stack_position; windows are first sorted
+ * by layer, then by stack_position within each layer.
+ */
+
+/* 
+ * Copyright (C) 2001 Havoc Pennington
+ * Copyright (C) 2005 Elijah Newren
+ * 
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License as
+ * published by the Free Software Foundation; either version 2 of the
+ * License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ * 
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA
+ * 02111-1307, USA.
+ */
+
+#ifndef META_STACK_H
+#define META_STACK_H
+
+#include "screen-private.h"
+
+/**
+ * Layers a window can be in.
+ * These MUST be in the order of stacking.
+ */
+typedef enum
+{
+  META_LAYER_DESKTOP        = 0,
+  META_LAYER_BOTTOM         = 1,
+  META_LAYER_NORMAL         = 2,
+  META_LAYER_TOP            = 4, /* Same as DOCK; see EWMH and bug 330717 */
+  META_LAYER_DOCK           = 4,
+  META_LAYER_FULLSCREEN     = 5,
+  META_LAYER_FOCUSED_WINDOW = 6,
+  META_LAYER_LAST           = 7
+} MetaStackLayer;
+
+/**
+ * A sorted list of windows bearing some level of resemblance to the stack of
+ * windows on the X server.
+ *
+ * (This is only used as a field within a MetaScreen; we treat it as a separate
+ * class for simplicity.)
+ */
+struct _MetaStack
+{
+  /** The MetaScreen containing this stack. */
+  MetaScreen *screen;
+
+  /**
+   * A sequence of all the Windows (X handles, not MetaWindows) of the windows
+   * we manage, sorted in order.  Suitable to be passed into _NET_CLIENT_LIST.
+   */
+  GArray *windows;
+
+  /** The MetaWindows of the windows we manage, sorted in order. */
+  GList *sorted;
+
+  /**
+   * MetaWindows waiting to be added to the "sorted" and "windows" list, after
+   * being added by meta_stack_add() and before being assimilated by
+   * stack_ensure_sorted().
+   *
+   * The order of the elements in this list is not important; what is important
+   * is the stack_position element of each window.
+   */
+  GList *added;
+
+  /**
+   * Windows (X handles, not MetaWindows) waiting to be removed from the
+   * "windows" list, after being removed by meta_stack_remove() and before
+   * being assimilated by stack_ensure_sorted().  (We already removed them
+   * from the "sorted" list.)
+   *
+   * The order of the elements in this list is not important.
+   */
+  GList *removed;
+  
+  /**
+   * If this is zero, the local stack oughtn't to be brought up to date with
+   * the X server's stack, because it is in the middle of being updated.
+   * If it is positive, the local stack is said to be "frozen", and will need
+   * to be thawed that many times before the stack can be brought up to date
+   * again.  You may freeze the stack with meta_stack_freeze() and thaw it
+   * with meta_stack_thaw().
+   */
+  int freeze_count;
+
+  /**
+   * The last-known stack of all windows, bottom to top.  We cache it here
+   * so that subsequent times we'll be able to do incremental moves.
+   */
+  GArray *last_root_children_stacked;
+
+  /**
+   * Number of stack positions; same as the length of added, but
+   * kept for quick reference.
+   */
+  gint n_positions;
+
+  /** Is the stack in need of re-sorting? */
+  unsigned int need_resort : 1;
+
+  /**
+   * Are the windows in the stack in need of having their
+   * layers recalculated?
+   */
+  unsigned int need_relayer : 1;
+
+  /**
+   * Are the windows in the stack in need of having their positions
+   * recalculated with respect to transiency (parent and child windows)?
+   */
+  unsigned int need_constrain : 1;
+};
+
+/**
+ * Creates and initialises a MetaStack.
+ *
+ * \param screen  The MetaScreen which will be the parent of this stack.
+ * \return The new screen.
+ */
+MetaStack *meta_stack_new       (MetaScreen     *screen);
+
+/**
+ * Destroys and frees a MetaStack.
+ *
+ * \param stack  The stack to destroy.
+ */
+void       meta_stack_free      (MetaStack      *stack);
+
+/**
+ * Adds a window to the local stack.  It is a fatal error to call this
+ * function on a window which already exists on the stack of any screen.
+ *
+ * \param window  The window to add
+ * \param stack  The stack to add it to
+ */
+void       meta_stack_add       (MetaStack      *stack,
+                                 MetaWindow     *window);
+
+/**
+ * Removes a window from the local stack.  It is a fatal error to call this
+ * function on a window which exists on the stack of any screen.
+ *
+ * \param window  The window to remove
+ * \param stack   The stack to remove it from
+ */
+void       meta_stack_remove    (MetaStack      *stack,
+                                 MetaWindow     *window);
+/**
+ * Recalculates the correct layer for all windows in the stack,
+ * and moves them about accordingly.
+ *
+ * \param window  Dummy parameter
+ * \param stack   The stack to recalculate
+ * \bug What's with the dummy parameter?
+ */
+void       meta_stack_update_layer    (MetaStack      *stack,
+                                       MetaWindow     *window);
+
+/**
+ * Recalculates the correct stacking order for all windows in the stack
+ * according to their transience, and moves them about accordingly.
+ *
+ * \param window  Dummy parameter
+ * \param stack   The stack to recalculate
+ * \bug What's with the dummy parameter?
+ */
+void       meta_stack_update_transient (MetaStack     *stack,
+                                        MetaWindow    *window);
+
+/**
+ * Move a window to the top of its layer.
+ *
+ * \param stack  The stack to modify.
+ * \param window  The window that's making an ascension.
+ *                (Amulet of Yendor not required.)
+ */
+void       meta_stack_raise     (MetaStack      *stack,
+                                 MetaWindow     *window);
+/**
+ * Move a window to the bottom of its layer.
+ *
+ * \param stack  The stack to modify.
+ * \param window  The window that's on the way downwards.
+ */
+void       meta_stack_lower     (MetaStack      *stack,
+                                 MetaWindow     *window);
+
+/**
+ * Prevent syncing to server until the next call of meta_stack_thaw(),
+ * so that we can carry out multiple operations in one go without having
+ * everything halfway reflected on the X server.
+ *
+ * (Calls to meta_stack_freeze() nest, so that multiple calls to
+ * meta_stack_freeze will require multiple calls to meta_stack_thaw().)
+ *
+ * \param stack  The stack to freeze.
+ */
+void       meta_stack_freeze    (MetaStack      *stack);
+
+/**
+ * Undoes a meta_stack_freeze(), and processes anything which has become
+ * necessary during the freeze.  It is an error to call this function if
+ * the stack has not been frozen.
+ *
+ * \param stack  The stack to thaw.
+ */
+void       meta_stack_thaw      (MetaStack      *stack);
+
+/**
+ * Finds the top window on the stack.
+ *
+ * \param stack  The stack to examine.
+ * \return The top window on the stack, or NULL in the vanishingly unlikely
+ *         event that you have no windows on your screen whatsoever.
+ */
+MetaWindow* meta_stack_get_top    (MetaStack  *stack);
+
+/**
+ * Finds the window at the bottom of the stack.  Since that's pretty much
+ * always the desktop, this isn't the most useful of functions, and nobody
+ * actually calls it.  We should probably get rid of it.
+ *
+ * \param stack  The stack to search
+ */
+MetaWindow* meta_stack_get_bottom (MetaStack  *stack);
+
+/**
+ * Finds the window above a given window in the stack.
+ * It is not an error to pass in a window which does not exist in
+ * the stack; the function will merely return NULL.
+ *
+ * \param stack   The stack to search.
+ * \param window  The window to look above.
+ * \param only_within_layer  If true, will return NULL if "window" is the
+ *                           top window in its layer.
+ * \return NULL if there is no such window;
+ *         the window above "window" otherwise.
+ */
+MetaWindow* meta_stack_get_above  (MetaStack  *stack,
+                                   MetaWindow *window,
+                                   gboolean    only_within_layer);
+
+/**
+ * Finds the window below a given window in the stack.
+ * It is not an error to pass in a window which does not exist in
+ * the stack; the function will merely return NULL.
+ *
+ * \param stack   The stack to search.
+ * \param window  The window to look below.
+ * \param only_within_layer  If true, will return NULL if "window" is the
+ *                           bottom window in its layer.
+ * \return NULL if there is no such window;
+ *         the window below "window" otherwise.
+ */
+MetaWindow* meta_stack_get_below  (MetaStack  *stack,
+                                   MetaWindow *window,
+                                   gboolean    only_within_layer);
+
+/**
+ * Find the topmost, focusable, mapped, window in a stack.  If you supply
+ * a window as "not_this_one", we won't return that one (presumably
+ * because it's going to be going away).  But if you do supply "not_this_one"
+ * and we find its parent, we'll return that; and if "not_this_one" is in
+ * a group, we'll return the top window of that group.
+ *
+ * Also, we are prejudiced against dock windows.  Every kind of window, even
+ * the desktop, will be returned in preference to a dock window.
+ *
+ * \param stack  The stack to search.
+ * \param workspace  NULL to search all workspaces; otherwise only windows
+ *                   from that workspace will be returned.
+ * \param not_this_one  Window to ignore because it's being unfocussed or
+ *                      going away.
+ * \return The window matching all these constraints or NULL if none does.
+ * 
+ * \bug Never called!
+  */
+MetaWindow* meta_stack_get_default_focus_window          (MetaStack     *stack,
+                                                          MetaWorkspace *workspace,
+                                                          MetaWindow    *not_this_one);
+
+/**
+ * Find the topmost, focusable, mapped, window in a stack.  If you supply
+ * a window as "not_this_one", we won't return that one (presumably
+ * because it's going to be going away).  But if you do supply "not_this_one"
+ * and we find its parent, we'll return that; and if "not_this_one" is in
+ * a group, we'll return the top window of that group.
+ *
+ * Also, we are prejudiced against dock windows.  Every kind of window, even
+ * the desktop, will be returned in preference to a dock window.
+ *
+ * \param stack  The stack to search.
+ * \param workspace  NULL to search all workspaces; otherwise only windows
+ *                   from that workspace will be returned.
+ * \param not_this_one  Window to ignore because it's being unfocussed or
+ *                      going away.
+ * \param root_x  The returned window must contain this point,
+ *                unless it's a dock.
+ * \param root_y  See root_x.
+ * \return The window matching all these constraints or NULL if none does.
+ */
+MetaWindow* meta_stack_get_default_focus_window_at_point (MetaStack     *stack,
+                                                          MetaWorkspace *workspace,
+                                                          MetaWindow    *not_this_one,
+                                                          int            root_x,
+                                                          int            root_y);
+
+/**
+ * Finds all the windows in the stack, in order.
+ *
+ * \param stack  The stack to examine.
+ * \param workspace  If non-NULL, only windows on this workspace will be
+ *                   returned; otherwise all windows in the stack will be
+ *                   returned.
+ * \return A list of windows, in stacking order, honouring layers.
+ */
+GList*      meta_stack_list_windows (MetaStack *stack,
+                                     MetaWorkspace *workspace);
+
+/**
+ * Comparison function for windows within a stack.  This is not directly
+ * suitable for use within a standard comparison routine, because it takes
+ * an extra parameter; you will need to wrap it.
+ *
+ * (FIXME: We could remove the stack parameter and use the stack of
+ * the screen of window A, and complain if the stack of the screen of
+ * window B differed; then this would be a usable general comparison function.)
+ *
+ * (FIXME: Apparently identical to compare_window_position(). Merge them.)
+ *
+ * \param stack  A stack containing both window_a and window_b
+ * \param window_a  A window
+ * \param window_b  Another window
+ * \return -1 if window_a is below window_b, honouring layers; 1 if it's
+ *         above it; 0 if you passed in the same window twice!
+ */
+int         meta_stack_windows_cmp  (MetaStack  *stack,
+                                     MetaWindow *window_a,
+                                     MetaWindow *window_b);
+
+/**
+ * Sets the position of a window within the stack.  This will only move it
+ * up or down within its layer.  It is an error to attempt to move this
+ * below position zero or above the last position in the stack (however, since
+ * we don't provide a simple way to tell the number of windows in the stack,
+ * this requirement may not be easy to fulfil).
+ *
+ * \param window  The window which is moving.
+ * \param position  Where it should move to (0 is the bottom).
+ */
+void meta_window_set_stack_position (MetaWindow *window,
+                                     int         position);
+
+/**
+ * Returns the current stack state, allowing rudimentary transactions.
+ *
+ * \param stack  The stack to examine.
+ * \return An opaque GList representing the current stack sort order;
+ *         it is the caller's responsibility to free it.
+ *         Pass this to meta_stack_set_positions() later if you want to restore
+ *         the state to where it was when you called this function.
+ */
+GList* meta_stack_get_positions (MetaStack *stack);
+
+/**
+ * Rolls back a transaction, given the list returned from
+ * meta_stack_get_positions().
+ *
+ * \param stack  The stack to roll back.
+ * \param windows  The list returned from meta_stack_get_positions().
+ */
+void   meta_stack_set_positions (MetaStack *stack,
+                                 GList     *windows);
+
+#endif