mutter/src/constraints.c

/* Metacity size/position constraints */

/*
 * Copyright (C) 2002, 2003 Red Hat, Inc.
 * Copyright (C) 2003, 2004 Rob Adams
 * 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.
 */

#include <config.h>
#include "constraints.h"
#include "workspace.h"
#include "place.h"

#include <stdlib.h>
#include <math.h>

#if 0
 // This is the short and sweet version of how to hack on this file; see
 // doc/how-constraints-works.txt for the gory details.  The basics of
 // understanding this file can be shown by the steps needed to add a new
 // constraint, which are:
 //   1) Add a new entry in the ConstraintPriority enum; higher values
 //      have higher priority
 //   2) Write a new function following the format of the example below,
 //      "constrain_whatever".
 //   3) Add your function to the all_constraints and all_constraint_names
 //      arrays (the latter of which is for debugging purposes)
 // 
 // An example constraint function, constrain_whatever:
 //
 // /* constrain_whatever does the following:
 //  *   Quits (returning true) if priority is higher than PRIORITY_WHATEVER
 //  *   If check_only is TRUE
 //  *     Returns whether the constraint is satisfied or not
 //  *   otherwise
 //  *     Enforces the constraint
 //  * Note that the value of PRIORITY_WHATEVER is centralized with the
 //  * priorities of other constraints in the definition of ConstrainPriority
 //  * for easier maintenance and shuffling of priorities.
 //  */
 // static gboolean
 // constrain_whatever (MetaWindow         *window,
 //                     ConstraintInfo     *info,
 //                     ConstraintPriority  priority,
 //                     gboolean            check_only)
 // {
 //   if (priority > PRIORITY_WHATEVER)
 //     return TRUE;
 //
 //   /* Determine whether constraint applies; note that if the constraint
 //    * cannot possibly be satisfied, constraint_applies should be set to
 //    * false.  If we don't do this, all constraints with a lesser priority
 //    * will be dropped along with this one, and we'd rather apply as many as
 //    * possible.
 //    */
 //   if (!constraint_applies)
 //     return TRUE;
 //
 //   /* Determine whether constraint is already satisfied; if we're only
 //    * checking the status of whether the constraint is satisfied, we end
 //    * here.
 //    */
 //   if (check_only || constraint_already_satisfied)
 //     return constraint_already_satisfied;
 //
 //   /* Enforce constraints */
 //   return TRUE;  /* Note that we exited early if check_only is FALSE; also,
 //                  * we know we can return TRUE here because we exited early
 //                  * if the constraint could not be satisfied; not that the
 //                  * return value is heeded in this case...
 //                  */
 // }
#endif

typedef enum
{
  PRIORITY_MINIMUM = 0, // Dummy value used for loop start = min(all priorities)
  PRIORITY_ASPECT_RATIO = 0,
  PRIORITY_ENTIRELY_VISIBLE_ON_SINGLE_XINERAMA = 0,
  PRIORITY_ENTIRELY_VISIBLE_ON_WORKAREA = 1,
  PRIORITY_SIZE_HINTS_INCREMENTS = 1,
  PRIORITY_MAXIMIZATION = 2,
  PRIORITY_FULLSCREEN = 2,
  PRIORITY_SIZE_HINTS_LIMITS = 3,
  PRIORITY_PARTIALLY_VISIBLE_ON_WORKAREA = 4,
  PRIORITY_MAXIMUM = 4  // Dummy value used for loop end = max(all priorities)
} ConstraintPriority;

typedef enum
{
  ACTION_MOVE,
  ACTION_RESIZE,
  ACTION_MOVE_AND_RESIZE
} ActionType;

typedef struct
{
  MetaRectangle        orig;
  MetaRectangle        current;
  MetaFrameGeometry   *fgeom;
  ActionType           action_type;
  gboolean             is_user_action;

  /* I know that these two things probably look similar at first, but they
   * have much different uses.  See doc/how-constraints-works.txt for for
   * explanation of the differences and similarity between resize_gravity
   * and fixed_directions
   */
  int                  resize_gravity;
  FixedDirections      fixed_directions;

  /* work_area_xinerama - current xinerama region minus struts
   * entire_xinerama    - current xienrama, including strut regions
   */
  MetaRectangle        work_area_xinerama;
  MetaRectangle        entire_xinerama;

  /* Spanning rectangles for the non-covered (by struts) region of the
   * screen and also for just the current xinerama
   */
  GList  *usable_screen_region;
  GList  *usable_xinerama_region;
} ConstraintInfo;

static gboolean constrain_maximization       (MetaWindow         *window,
                                              ConstraintInfo     *info,
                                              ConstraintPriority  priority,
                                              gboolean            check_only);
static gboolean constrain_fullscreen         (MetaWindow         *window,
                                              ConstraintInfo     *info,
                                              ConstraintPriority  priority,
                                              gboolean            check_only);
static gboolean constrain_size_increments    (MetaWindow         *window,
                                              ConstraintInfo     *info,
                                              ConstraintPriority  priority,
                                              gboolean            check_only);
static gboolean constrain_size_limits        (MetaWindow         *window,
                                              ConstraintInfo     *info,
                                              ConstraintPriority  priority,
                                              gboolean            check_only);
static gboolean constrain_aspect_ratio       (MetaWindow         *window,
                                              ConstraintInfo     *info,
                                              ConstraintPriority  priority,
                                              gboolean            check_only);
static gboolean constrain_to_single_xinerama (MetaWindow         *window,
                                              ConstraintInfo     *info,
                                              ConstraintPriority  priority,
                                              gboolean            check_only);
static gboolean constrain_fully_onscreen     (MetaWindow         *window,
                                              ConstraintInfo     *info,
                                              ConstraintPriority  priority,
                                              gboolean            check_only);
static gboolean constrain_partially_onscreen (MetaWindow         *window,
                                              ConstraintInfo     *info,
                                              ConstraintPriority  priority,
                                              gboolean            check_only);

static void setup_constraint_info        (ConstraintInfo      *info,
                                          MetaWindow          *window,
                                          MetaFrameGeometry   *orig_fgeom,
                                          MetaMoveResizeFlags  flags,
                                          int                  resize_gravity,
                                          const MetaRectangle *orig,
                                          MetaRectangle       *new);
static void place_window_if_needed       (MetaWindow     *window,
                                          ConstraintInfo *info);
static void update_onscreen_requirements (MetaWindow     *window,
                                          ConstraintInfo *info);
static void extend_by_frame              (MetaRectangle           *rect,
                                          const MetaFrameGeometry *fgeom);
static void unextend_by_frame            (MetaRectangle           *rect,
                                          const MetaFrameGeometry *fgeom);
static inline void get_size_limits       (const MetaWindow        *window,
                                          const MetaFrameGeometry *fgeom,
                                          gboolean include_frame,
                                          MetaRectangle *min_size,
                                          MetaRectangle *max_size);

typedef gboolean (* ConstraintFunc) (MetaWindow         *window,
                                     ConstraintInfo     *info,
                                     ConstraintPriority  priority,
                                     gboolean            check_only);

typedef struct {
  ConstraintFunc func;
  const char* name;
} Constraint;

static const Constraint all_constraints[] = {
  {constrain_maximization,       "constrain_maximization"},
  {constrain_fullscreen,         "constrain_fullscreen"},
  {constrain_size_increments,    "constrain_size_increments"},
  {constrain_size_limits,        "constrain_size_limits"},
  {constrain_aspect_ratio,       "constrain_aspect_ratio"},
  {constrain_to_single_xinerama, "constrain_to_single_xinerama"},
  {constrain_fully_onscreen,     "constrain_fully_onscreen"},
  {constrain_partially_onscreen, "constrain_partially_onscreen"},
  {NULL,                         NULL}
};

static gboolean
do_all_constraints (MetaWindow         *window,
                    ConstraintInfo     *info,
                    ConstraintPriority  priority,
                    gboolean            check_only)
{
  const Constraint *constraint;
  gboolean          satisfied;

  constraint = &all_constraints[0];
  satisfied = TRUE;
  while (constraint->func != NULL)
    {
      satisfied = satisfied &&
                  (*constraint->func) (window, info, priority, check_only);

      if (!check_only)
        {
          /* Log how the constraint modified the position */
          meta_topic (META_DEBUG_GEOMETRY,
                      "info->current is %d,%d +%d,%d after %s\n",
                      info->current.x, info->current.y, 
                      info->current.width, info->current.height,
                      constraint->name);
        }
      else if (!satisfied)
        {
          /* Log which constraint was not satisfied */
          meta_topic (META_DEBUG_GEOMETRY,
                      "constraint %s not satisfied.\n",
                      constraint->name);
          return FALSE;
        }
      ++constraint;
    }

  return TRUE;
}

void
meta_window_constrain (MetaWindow          *window,
                       MetaFrameGeometry   *orig_fgeom,
                       MetaMoveResizeFlags  flags,
                       int                  resize_gravity,
                       const MetaRectangle *orig,
                       MetaRectangle       *new)
{
  ConstraintInfo info;

  /* WARNING: orig and new specify positions and sizes of the inner window,
   * not the outer.  This is a common gotcha since half the constraints
   * deal with inner window position/size and half deal with outer.  See
   * doc/how-constraints-works.txt for more information.
   */
  meta_topic (META_DEBUG_GEOMETRY,
              "Constraining %s in move from %d,%d %dx%d to %d,%d %dx%d\n",
              window->desc,
              orig->x, orig->y, orig->width, orig->height,
              new->x,  new->y,  new->width,  new->height);

  setup_constraint_info (&info,
                         window, 
                         orig_fgeom, 
                         flags,
                         resize_gravity,
                         orig,
                         new);
  place_window_if_needed (window, &info);

  ConstraintPriority priority = PRIORITY_MINIMUM;
  gboolean satisfied = FALSE;
  while (!satisfied && priority <= PRIORITY_MAXIMUM) {
    gboolean check_only = TRUE;

    /* Individually enforce all the high-enough priority constraints */
    do_all_constraints (window, &info, priority, !check_only);

    /* Check if all high-enough priority constraints are simultaneously 
     * satisfied
     */
    satisfied = do_all_constraints (window, &info, priority, check_only);

    /* Drop the least important constraints if we can't satisfy them all */
    priority++;
  }

  /* Make sure we use the constrained position */
  *new = info.current;

  /* We may need to update window->require_fully_onscreen,
   * window->require_on_single_xinerama, and perhaps other quantities
   * if this was a user move or user move-and-resize operation.
   */
  update_onscreen_requirements (window, &info);

  /* Ew, what an ugly way to do things.  Destructors (in a real OOP language,
   * not gobject-style--gobject would be more pain than it's worth) or
   * smart pointers would be so much nicer here.  *shrug*
   */
  if (!orig_fgeom)
    g_free (info.fgeom);
}

static void
setup_constraint_info (ConstraintInfo      *info,
                       MetaWindow          *window,
                       MetaFrameGeometry   *orig_fgeom,
                       MetaMoveResizeFlags  flags,
                       int                  resize_gravity,
                       const MetaRectangle *orig,
                       MetaRectangle       *new)
{
  info->orig    = *orig;
  info->current = *new;

  /* Create a fake frame geometry if none really exists */
  if (orig_fgeom && !window->fullscreen)
    info->fgeom = orig_fgeom;
  else
    info->fgeom = g_new0 (MetaFrameGeometry, 1);

  if (flags & META_IS_MOVE_ACTION && flags & META_IS_RESIZE_ACTION)
    info->action_type = ACTION_MOVE_AND_RESIZE;
  else if (flags & META_IS_RESIZE_ACTION)
    info->action_type = ACTION_RESIZE;
  else if (flags & META_IS_MOVE_ACTION)
    info->action_type = ACTION_MOVE_AND_RESIZE;
  else
    g_error ("BAD, BAD developer!  No treat for you!  (Fix your calls to "
             "meta_window_move_resize_internal()).\n");

  info->is_user_action = (flags & META_IS_USER_ACTION);

  info->resize_gravity = resize_gravity;

  info->fixed_directions = 0;
  /* If x directions don't change but either y direction does */
  if ( orig->x == new->x && orig->x + orig->width  == new->x + new->width   &&
      (orig->y != new->y || orig->y + orig->height != new->y + new->height))
    {
      info->fixed_directions = FIXED_DIRECTION_X;
    }
  /* If y directions don't change but either x direction does */
  if ( orig->y == new->y && orig->y + orig->height == new->y + new->height  &&
      (orig->x != new->x || orig->x + orig->width  != new->x + new->width ))
    {
      info->fixed_directions = FIXED_DIRECTION_Y;
    }

  meta_window_get_work_area_current_xinerama (window, &info->work_area_xinerama);

  const MetaXineramaScreenInfo *xinerama_info =
    meta_screen_get_xinerama_for_window (window->screen, window);
  info->entire_xinerama = xinerama_info->rect;

  MetaWorkspace *cur_workspace = window->screen->active_workspace;
  info->usable_screen_region   = 
    meta_workspace_get_onscreen_region (cur_workspace);
  info->usable_xinerama_region = 
    meta_workspace_get_onxinerama_region (cur_workspace, 
                                          xinerama_info->number);

  /* Log all this information for debugging */
  meta_topic (META_DEBUG_GEOMETRY,
              "Setting up constraint info:\n"
              "  orig: %d,%d +%d,%d\n"
              "  new : %d,%d +%d,%d\n"
              "  fgeom: %d,%d,%d,%d\n"
              "  action_type     : %s\n"
              "  is_user_action  : %s\n"
              "  resize_gravity  : %s\n"
              "  fixed_directions: %s\n"
              "  work_area_xinerama: %d,%d +%d,%d\n"
              "  entire_xinerama   : %d,%d +%d,%d\n",
              info->orig.x, info->orig.y, info->orig.width, info->orig.height,
              info->current.x, info->current.y, 
                info->current.width, info->current.height,
              info->fgeom->left_width, info->fgeom->right_width,
                info->fgeom->top_height, info->fgeom->bottom_height,
              (info->action_type == ACTION_MOVE) ? "Move" :
                (info->action_type == ACTION_RESIZE) ? "Resize" :
                (info->action_type == ACTION_MOVE_AND_RESIZE) ? "Move&Resize" :
                "Freakin' Invalid Stupid",
              (info->is_user_action) ? "true" : "false",
              meta_gravity_to_string (info->resize_gravity),
              (info->fixed_directions == 0) ? "None" :
                (info->fixed_directions == FIXED_DIRECTION_X) ? "X fixed" :
                (info->fixed_directions == FIXED_DIRECTION_Y) ? "Y fixed" :
                "Freakin' Invalid Stupid",
              info->work_area_xinerama.x, info->work_area_xinerama.y,
                info->work_area_xinerama.width, 
                info->work_area_xinerama.height,
              info->entire_xinerama.x, info->entire_xinerama.y,
                info->entire_xinerama.width, info->entire_xinerama.height);
}

static void
place_window_if_needed(MetaWindow     *window,
                       ConstraintInfo *info)
{
  gboolean did_placement;

  /* Do placement if any, so we go ahead and apply position
   * constraints in a move-only context. Don't place
   * maximized/fullscreen windows until they are unmaximized
   * and unfullscreened
   */
  did_placement = FALSE;
  if (!window->placed &&
      window->calc_placement &&
      !META_WINDOW_MAXIMIZED (window) &&
      !window->fullscreen)
    {
      MetaRectangle placed_rect = info->orig;

      meta_window_place (window, info->fgeom, info->orig.x, info->orig.y,
                         &placed_rect.x, &placed_rect.y);
      did_placement = TRUE;

      /* placing the window may have changed the xinerama.  Find the
       * new xinerama and update the ConstraintInfo
       */
      const MetaXineramaScreenInfo *xinerama_info =
        meta_screen_get_xinerama_for_rect (window->screen, &placed_rect);
      info->entire_xinerama = xinerama_info->rect;
      meta_window_get_work_area_for_xinerama (window,
                                              xinerama_info->number,
                                              &info->work_area_xinerama);
      MetaWorkspace *cur_workspace = window->screen->active_workspace;
      info->usable_xinerama_region = 
        meta_workspace_get_onxinerama_region (cur_workspace, 
                                              xinerama_info->number);


      info->current.x = placed_rect.x;
      info->current.y = placed_rect.y;

      /* Since we just barely placed the window, there's no reason to
       * consider any of the directions fixed.
       */
      info->fixed_directions = 0;
    }

  if ((window->maximize_horizontally_after_placement ||
       window->maximize_vertically_after_placement) &&
      (window->placed || did_placement))
    {
      /* define a sane saved_rect so that the user can unmaximize to
       * something reasonable.
       */
      if (info->current.width >= info->work_area_xinerama.width)
        {
          info->current.width = .75 * info->work_area_xinerama.width;
          info->current.x = info->work_area_xinerama.x +
                   .125 * info->work_area_xinerama.width;
        }
      if (info->current.height >= info->work_area_xinerama.height)
        {
          info->current.height = .75 * info->work_area_xinerama.height;
          info->current.y = info->work_area_xinerama.y +
                   .083 * info->work_area_xinerama.height;
        }

      if (window->maximize_horizontally_after_placement &&
          window->maximize_vertically_after_placement)
        meta_window_maximize_internal (window,   
                                       META_MAXIMIZE_HORIZONTAL |
                                       META_MAXIMIZE_VERTICAL,
                                       &info->current);
      else if (window->maximize_horizontally_after_placement)
        {
          info->current.x = info->work_area_xinerama.x
            + info->fgeom->left_width;
          info->current.width = info->work_area_xinerama.width
            - info->fgeom->left_width - info->fgeom->right_width;
        }
      else if (window->maximize_vertically_after_placement);
        {
          info->current.y = info->work_area_xinerama.y
            + info->fgeom->top_height;
          info->current.height = info->work_area_xinerama.height
            - info->fgeom->top_height - info->fgeom->bottom_height;
        }

      /* maximization may have changed frame geometry */
      if (window->frame && !window->fullscreen)
        meta_frame_calc_geometry (window->frame, info->fgeom);

      window->maximize_horizontally_after_placement = FALSE;
      window->maximize_vertically_after_placement = FALSE;
    }
}

static void
update_onscreen_requirements (MetaWindow     *window,
                              ConstraintInfo *info)
{
  gboolean old;

  /* We only apply the various onscreen requirements to normal windows */
  if (window->type == META_WINDOW_DESKTOP ||
      window->type == META_WINDOW_DOCK)
    return;

  /* USABILITY NOTE: Naturally, I only want the require_fully_onscreen and
   * require_on_single_xinerama flags to *become false* due to user
   * interactions (which is allowed since certain constraints are ignored
   * for user interactions regardless of the setting of these flags).
   * However, whether to make these flags *become true* due to just an
   * application interaction is a little trickier.  It's possible that
   * users may find not doing that strange since two application
   * interactions that resize in opposite ways don't necessarily end up
   * cancelling--but it may also be strange for the user to have an
   * application resize the window so that it's onscreen, the user forgets
   * about it, and then later the app is able to resize itself off the
   * screen.  Anyway, for now, I'm think the latter is the more problematic
   * case but this may need to be revisited.
   */

  /* The require onscreen/on-single-xinerama stuff is relative to the
   * outer window, not the inner
   */
  extend_by_frame (&info->current, info->fgeom);

  /* Update whether we want future constraint runs to require the
   * window to be on fully onscreen.
   */
  old = window->require_fully_onscreen;
  window->require_fully_onscreen =
    meta_rectangle_contained_in_region (info->usable_screen_region,
                                        &info->current);
  if (old ^ window->require_fully_onscreen)
    meta_topic (META_DEBUG_GEOMETRY,
                "require_fully_onscreen for %s toggled to %s\n",
                window->desc,
                window->require_fully_onscreen ? "TRUE" : "FALSE");

  /* Update whether we want future constraint runs to require the
   * window to be on a single xinerama.
   */
  old = window->require_on_single_xinerama;
  window->require_on_single_xinerama =
    meta_rectangle_contained_in_region (info->usable_xinerama_region,
                                        &info->current);
  if (old ^ window->require_on_single_xinerama)
    meta_topic (META_DEBUG_GEOMETRY,
                "require_on_single_xinerama for %s toggled to %s\n",
                window->desc, 
                window->require_on_single_xinerama ? "TRUE" : "FALSE");

  /* Don't forget to restore the position of the window */
  unextend_by_frame (&info->current, info->fgeom);
}

static void
extend_by_frame (MetaRectangle           *rect,
                 const MetaFrameGeometry *fgeom)
{
  rect->x -= fgeom->left_width;
  rect->y -= fgeom->top_height;
  rect->width  += fgeom->left_width + fgeom->right_width;
  rect->height += fgeom->top_height + fgeom->bottom_height;
}

static void
unextend_by_frame (MetaRectangle           *rect,
                   const MetaFrameGeometry *fgeom)
{
  rect->x += fgeom->left_width;
  rect->y += fgeom->top_height;
  rect->width  -= fgeom->left_width + fgeom->right_width;
  rect->height -= fgeom->top_height + fgeom->bottom_height;
}

static inline void
get_size_limits (const MetaWindow        *window,
                 const MetaFrameGeometry *fgeom,
                 gboolean                 include_frame,
                 MetaRectangle *min_size,
                 MetaRectangle *max_size)
{
  /* We pack the results into MetaRectangle structs just for convienience; we
   * don't actually use the position of those rects.
   */
  min_size->width  = window->size_hints.min_width;
  min_size->height = window->size_hints.min_height;
  max_size->width  = window->size_hints.max_width;
  max_size->height = window->size_hints.max_height;

  if (include_frame)
    {
      int fw = fgeom->left_width + fgeom->right_width;
      int fh = fgeom->top_height + fgeom->bottom_height;

      min_size->width  += fw;
      min_size->height += fh;
      max_size->width  += fw;
      max_size->height += fh;
    }
}

static gboolean
constrain_maximization (MetaWindow         *window,
                        ConstraintInfo     *info,
                        ConstraintPriority  priority,
                        gboolean            check_only)
{
  if (priority > PRIORITY_MAXIMIZATION)
    return TRUE;

  /* Determine whether constraint applies; exit if it doesn't */
  if (!window->maximized_horizontally && !window->maximized_vertically)
    return TRUE;

  MetaRectangle min_size, max_size;
  MetaRectangle work_area = info->work_area_xinerama;
  unextend_by_frame (&work_area, info->fgeom);
  get_size_limits (window, info->fgeom, FALSE, &min_size, &max_size);

  gboolean hminbad, vminbad, hmaxbad, vmaxbad;
  hminbad = work_area.width < min_size.width && window->maximized_horizontally;
  vminbad = work_area.height < min_size.height && window->maximized_vertically;
  hmaxbad = work_area.width > max_size.width && window->maximized_horizontally;
  vmaxbad = work_area.height > max_size.height && window->maximized_vertically;
  if (hminbad || vminbad || hmaxbad || vmaxbad)
    return TRUE;

  /* Determine whether constraint is already satisfied; exit if it is */
  gboolean horiz_equal, vert_equal;
  horiz_equal = work_area.x      == info->current.x &&
                work_area.width  == info->current.width;
  vert_equal  = work_area.y      == info->current.y &&
                work_area.height == info->current.height;
  gboolean constraint_already_satisfied =
    (horiz_equal || !window->maximized_horizontally) &&
    (vert_equal  || !window->maximized_vertically);
  if (check_only || constraint_already_satisfied)
    return constraint_already_satisfied;

  /*** Enforce constraint ***/
  if (window->maximized_horizontally)
    {
      info->current.x      = work_area.x;
      info->current.width  = work_area.width;
    }
  if (window->maximized_vertically)
    {
      info->current.y      = work_area.y;
      info->current.height = work_area.height;
    }
  return TRUE;
}

static gboolean
constrain_fullscreen (MetaWindow         *window,
                      ConstraintInfo     *info,
                      ConstraintPriority  priority,
                      gboolean            check_only)
{
  if (priority > PRIORITY_FULLSCREEN)
    return TRUE;

  /* Determine whether constraint applies; exit if it doesn't */
  if (!window->fullscreen)
    return TRUE;
  MetaRectangle min_size, max_size;
  MetaRectangle xinerama = info->entire_xinerama;
  get_size_limits (window, info->fgeom, FALSE, &min_size, &max_size);
  gboolean too_big =   !meta_rectangle_could_fit_rect (&xinerama, &min_size);
  gboolean too_small = !meta_rectangle_could_fit_rect (&max_size, &xinerama);
  if (too_big || too_small)
    return TRUE;

  /* Determine whether constraint is already satisfied; exit if it is */
  gboolean constraint_already_satisfied =
    meta_rectangle_equal (&info->current, &xinerama);
  if (check_only || constraint_already_satisfied)
    return constraint_already_satisfied;

  /*** Enforce constraint ***/
  info->current = xinerama;
  return TRUE;
}

static gboolean
constrain_size_increments (MetaWindow         *window,
                           ConstraintInfo     *info,
                           ConstraintPriority  priority,
                           gboolean            check_only)
{
  if (priority > PRIORITY_SIZE_HINTS_INCREMENTS)
    return TRUE;

  /* Determine whether constraint applies; exit if it doesn't */
  if (META_WINDOW_MAXIMIZED (window) || window->fullscreen || 
      info->action_type == ACTION_MOVE)
    return TRUE;

  /* Determine whether constraint is already satisfied; exit if it is */
  int bh, hi, bw, wi, extra_height, extra_width;
  bh = window->size_hints.base_height;
  hi = window->size_hints.height_inc;
  bw = window->size_hints.base_width;
  wi = window->size_hints.width_inc;
  extra_height = (info->current.height - bh) % hi;
  extra_width  = (info->current.width  - bw) % wi;
  if (window->maximized_horizontally)
    extra_width *= 0;
  if (window->maximized_vertically)
    extra_height *= 0;
  gboolean constraint_already_satisfied = 
    (extra_height == 0 && extra_width == 0);

  if (check_only || constraint_already_satisfied)
    return constraint_already_satisfied;

  /*** Enforce constraint ***/
  /* Shrink to base + N * inc */
  meta_rectangle_resize_with_gravity (&info->orig,
                                      &info->current, 
                                      info->resize_gravity,
                                      info->current.width - extra_width,
                                      info->current.height - extra_height);
  return TRUE;
}

static gboolean
constrain_size_limits (MetaWindow         *window,
                       ConstraintInfo     *info,
                       ConstraintPriority  priority,
                       gboolean            check_only)
{
  if (priority > PRIORITY_SIZE_HINTS_LIMITS)
    return TRUE;

  /* Determine whether constraint applies; exit if it doesn't.
   *
   * Note: The old code didn't apply this constraint for fullscreen or
   * maximized windows--but that seems odd to me.  *shrug*
   */
  if (info->action_type == ACTION_MOVE)
    return TRUE;

  /* Determine whether constraint is already satisfied; exit if it is */
  MetaRectangle min_size, max_size;
  get_size_limits (window, info->fgeom, FALSE, &min_size, &max_size);
  gboolean too_big =   
    !meta_rectangle_could_fit_rect (&info->current, &min_size);
  gboolean too_small = 
    !meta_rectangle_could_fit_rect (&max_size, &info->current);
  gboolean constraint_already_satisfied = !too_big && !too_small;
  if (check_only || constraint_already_satisfied)
    return constraint_already_satisfied;

  /*** Enforce constraint ***/
  int new_width, new_height;
  new_width  = CLAMP (info->current.width,  min_size.width,  max_size.width);
  new_height = CLAMP (info->current.height, min_size.height, max_size.height);
  meta_rectangle_resize_with_gravity (&info->orig,
                                      &info->current, 
                                      info->resize_gravity,
                                      new_width,
                                      new_height);
  return TRUE;
}

static gboolean
constrain_aspect_ratio (MetaWindow         *window,
                        ConstraintInfo     *info,
                        ConstraintPriority  priority,
                        gboolean            check_only)
{
  if (priority > PRIORITY_ASPECT_RATIO)
    return TRUE;

  /* Determine whether constraint applies; exit if it doesn't. */
  double minr, maxr;
  minr =         window->size_hints.min_aspect.x /
         (double)window->size_hints.min_aspect.y;
  maxr =         window->size_hints.max_aspect.x /
         (double)window->size_hints.max_aspect.y;
  gboolean constraints_are_inconsistent = minr > maxr;
  if (constraints_are_inconsistent ||
      META_WINDOW_MAXIMIZED (window) || window->fullscreen || 
      info->action_type == ACTION_MOVE)
    return TRUE;

  /* Determine whether constraint is already satisfied; exit if it is.  We
   * need the following to hold:
   *
   *                 width
   *         minr <= ------ <= maxr
   *                 height
   *
   * But we need to allow for some slight fudging since width and height
   * are integers instead of floating point numbers (this is particularly
   * important when minr == maxr), so we allow width and height to be off
   * a little bit from strictly satisfying these equations.  For just one
   * sided resizing, we have to make the fudge factor a little bigger
   * because of how meta_rectangle_resize_with_gravity treats those as
   * being a resize increment (FIXME: I should handle real resize
   * increments better here...)
   */
  int fudge;
  switch (info->resize_gravity)
    {
    case WestGravity:
    case NorthGravity:
    case SouthGravity:
    case EastGravity:
      fudge = 2;
      break;

    case NorthWestGravity:
    case SouthWestGravity:
    case CenterGravity:
    case NorthEastGravity:
    case SouthEastGravity:
    case StaticGravity:
    default:
      fudge = 1;
      break;
    }
  gboolean constraint_already_satisfied = 
    info->current.width - (info->current.height * minr ) > -minr*fudge &&
    info->current.width - (info->current.height * maxr ) <  maxr*fudge;
  if (check_only || constraint_already_satisfied)
    return constraint_already_satisfied;

  /*** Enforce constraint ***/
  int new_width, new_height;
  double best_width, best_height;
  double alt_width, alt_height;
  new_width = info->current.width;
  new_height = info->current.height;

  switch (info->resize_gravity)
    {
    case WestGravity:
    case EastGravity:
      /* Yeah, I suck for doing implicit rounding -- sue me */
      new_height = CLAMP (new_height, new_width / maxr,  new_width / minr);
      break;

    case NorthGravity:
    case SouthGravity:
      /* Yeah, I suck for doing implicit rounding -- sue me */
      new_width  = CLAMP (new_width,  new_height * minr, new_height * maxr);
      break;

    case NorthWestGravity:
    case SouthWestGravity:
    case CenterGravity:
    case NorthEastGravity:
    case SouthEastGravity:
    case StaticGravity:
    default:
      /* Find what width would correspond to new_height, and what height would
       * correspond to new_width */
      alt_width  = CLAMP (new_width,  new_height * minr, new_height * maxr);
      alt_height = CLAMP (new_height, new_width / maxr,  new_width / minr);

      /* The line connecting the points (alt_width, new_height) and
       * (new_width, alt_height) provide a range of
       * valid-for-the-aspect-ratio-constraint sizes.  We want the
       * size in that range closest to the value requested, i.e. the
       * point on the line which is closest to the point (new_width,
       * new_height)
       */
      meta_rectangle_find_linepoint_closest_to_point (alt_width, new_height,
                                                      new_width, alt_height,
                                                      new_width, new_height,
                                                      &best_width, &best_height);

      /* Yeah, I suck for doing implicit rounding -- sue me */
      new_width  = best_width;
      new_height = best_height;

      break;
    }

  meta_rectangle_resize_with_gravity (&info->orig,
                                      &info->current, 
                                      info->resize_gravity,
                                      new_width,
                                      new_height);

  return TRUE;
}

static gboolean
do_screen_and_xinerama_relative_constraints (
  MetaWindow     *window,
  GList          *region_spanning_rectangles,
  ConstraintInfo *info,
  gboolean        check_only)
{
  gboolean exit_early = FALSE;

  /* First, log some debugging information */
  char spanning_region[1 + 28 * g_list_length (region_spanning_rectangles)];
  (void) spanning_region;  /* Avoid stupid & incorrect compiler warnings... */
  meta_topic (META_DEBUG_GEOMETRY,
              "screen/xinerama constraint; region_spanning_rectangles: %s\n",
              meta_rectangle_region_to_string (region_spanning_rectangles, ", ", 
                                               spanning_region));

  /* Determine whether constraint applies; exit if it doesn't */
  MetaRectangle how_far_it_can_be_smushed, min_size, max_size;
  how_far_it_can_be_smushed = info->current;
  get_size_limits (window, info->fgeom, TRUE, &min_size, &max_size);
  extend_by_frame (&info->current, info->fgeom);

  if (info->action_type != ACTION_MOVE)
    {
      if (!(info->fixed_directions & FIXED_DIRECTION_X))
        how_far_it_can_be_smushed.width = min_size.width;

      if (!(info->fixed_directions & FIXED_DIRECTION_Y))
        how_far_it_can_be_smushed.height = min_size.height;
    }
  if (!meta_rectangle_could_fit_in_region (region_spanning_rectangles,
                                           &how_far_it_can_be_smushed))
    exit_early = TRUE;

  /* Determine whether constraint is already satisfied; exit if it is */
  gboolean constraint_satisfied = 
    meta_rectangle_contained_in_region (region_spanning_rectangles,
                                        &info->current);
  if (exit_early || constraint_satisfied || check_only)
    {
      unextend_by_frame (&info->current, info->fgeom);
      return constraint_satisfied;
    }

  /* Enforce constraint */

  /* Clamp rectangle size for resize or move+resize actions */
  if (info->action_type != ACTION_MOVE)
    meta_rectangle_clamp_to_fit_into_region (region_spanning_rectangles,
                                             info->fixed_directions,
                                             &info->current,
                                             &min_size);

  if (info->is_user_action && info->action_type == ACTION_RESIZE)
    /* For user resize, clip to the relevant region */
    meta_rectangle_clip_to_region (region_spanning_rectangles,
                                   info->fixed_directions,
                                   &info->current);
  else
    /* For everything else, shove the rectangle into the relevant region */
    meta_rectangle_shove_into_region (region_spanning_rectangles,
                                      info->fixed_directions,
                                      &info->current);

  unextend_by_frame (&info->current, info->fgeom);
  return TRUE;
}

static gboolean
constrain_to_single_xinerama (MetaWindow         *window,
                              ConstraintInfo     *info,
                              ConstraintPriority  priority,
                              gboolean            check_only)
{
  if (priority > PRIORITY_ENTIRELY_VISIBLE_ON_SINGLE_XINERAMA)
    return TRUE;

  /* Exit early if we know the constraint won't apply--note that this constraint
   * is only meant for normal windows (e.g. we don't want docks to be shoved 
   * "onscreen" by their own strut) and we can't apply it to frameless windows
   * or else users will be unable to move windows such as XMMS across xineramas.
   */
  if (window->type == META_WINDOW_DESKTOP   ||
      window->type == META_WINDOW_DOCK      ||
      window->screen->n_xinerama_infos == 1 ||
      !window->require_on_single_xinerama   ||
      !window->frame                        ||
      info->is_user_action)
    return TRUE;

  /* Have a helper function handle the constraint for us */
  gboolean retval =
    do_screen_and_xinerama_relative_constraints (window, 
                                                 info->usable_xinerama_region,
                                                 info,
                                                 check_only);

  /* Free up the data we allocated */
  return retval;
}

static gboolean
constrain_fully_onscreen (MetaWindow         *window,
                          ConstraintInfo     *info,
                          ConstraintPriority  priority,
                          gboolean            check_only)
{
  if (priority > PRIORITY_ENTIRELY_VISIBLE_ON_WORKAREA)
    return TRUE;

  /* Exit early if we know the constraint won't apply--note that this constraint
   * is only meant for normal windows (e.g. we don't want docks to be shoved 
   * "onscreen" by their own strut).
   */
  if (window->type == META_WINDOW_DESKTOP ||
      window->type == META_WINDOW_DOCK    ||
      !window->require_fully_onscreen     || 
      info->is_user_action)
    return TRUE;

  /* Have a helper function handle the constraint for us */
  gboolean retval =
    do_screen_and_xinerama_relative_constraints (window, 
                                                 info->usable_screen_region,
                                                 info,
                                                 check_only);

  return retval;
}

static gboolean
constrain_partially_onscreen (MetaWindow         *window,
                              ConstraintInfo     *info,
                              ConstraintPriority  priority,
                              gboolean            check_only)
{
  if (priority > PRIORITY_PARTIALLY_VISIBLE_ON_WORKAREA)
    return TRUE;

  /* Exit early if we know the constraint won't apply--note that this constraint
   * is only meant for normal windows (e.g. we don't want docks to be shoved 
   * "onscreen" by their own strut).
   */
  if (window->type == META_WINDOW_DESKTOP ||
      window->type == META_WINDOW_DOCK)
    return TRUE;

  /* Determine how much offscreen things are allowed.  We first need to
   * figure out how much must remain on the screen.  For that, we use 25%
   * window width/height but clamp to the range of (10,75) pixels.  This is
   * somewhat of a seat of my pants random guess at what might look good.
   * Then, the amount that is allowed off is just the window size minus
   * this amount.
   */
  int horiz_amount = info->current.width  / 4;
  int vert_amount  = info->current.height / 4;
  horiz_amount = CLAMP (horiz_amount, 10, 75);
  vert_amount  = CLAMP (vert_amount,  10, 75);
  horiz_amount = info->current.width - horiz_amount;
  vert_amount  = info->current.height - vert_amount;

  /* Extend the region, have a helper function handle the constraint,
   * then return the region to its original size.
   */
  meta_rectangle_expand_region (info->usable_screen_region,
                                horiz_amount,
                                horiz_amount, 
                                vert_amount,
                                vert_amount);
  gboolean retval =
    do_screen_and_xinerama_relative_constraints (window, 
                                                 info->usable_screen_region,
                                                 info,
                                                 check_only);
  meta_rectangle_expand_region (info->usable_screen_region,
                                -horiz_amount,
                                -horiz_amount, 
                                -vert_amount,
                                -vert_amount);

  return retval;
}