mutter/src/constraints.c

/* Metacity size/position constraints */

/*
 * Copyright (C) 2002, 2003 Red Hat, Inc.
 *
 * 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 "window.h"
#include "workspace.h"
#include "place.h"

/* The way this code works was suggested by Owen Taylor.
 *
 * For any move_resize, we determine which variables are "free
 * variables" and apply constraints in terms of those. During the move
 * resize, we only want to modify those variables; otherwise the
 * constraint process can have peculiar side effects when the size and
 * position constraints interact. For example, resizing a window from
 * the top might go wrong when position constraints apply to the top
 * edge, and result in the bottom edge moving downward while the top
 * stays fixed.
 *
 * After selecting the variables we plan to vary, we define
 * each constraint on the window in terms of those variables.
 *
 * Trivial example, say we are resizing vertically from the top of the
 * window. In that case we are applying the user's mouse motion delta
 * to an original size and position, note that dy is positive to
 * resize downward:
 *
 *   new_height = orig_height - dy;
 *   new_y      = orig_y + dy;
 *
 * A constraint that the position can't go above the top panel would
 * look like this:
 *
 *   new_y >= screen_top_bound
 *
 * Substitute:
 *
 *   orig_y + dy >= screen_top_bound
 *
 * Find the "boundary point" by changing to an equality:
 *
 *   orig_y + dy = screen_top_bound
 *
 * Solve:
 *
 *   dy = screen_top_bound - orig_y
 *
 * This dy is now the _maximum_ dy and you constrain dy with that
 * value, applying it to both the move and the resize:
 *
 *   new_height = orig_height - dy;
 *   new_y      = orig_y + dy;
 *
 * This way the constraint is applied simultaneously to size/position,
 * so you aren't running the risk of constraining one but still
 * changing the other. i.e. we've converted an operation that may
 * modify both the Y position and the height of the window into an
 * operation that modifies a single variable, dy.  That variable is
 * then constrained, rather than the constraining the Y pos and height
 * separately. This is a rather complicated fix for an obscure bug
 * that happened when resizing a window and encountering a constraint
 * such as the top edge of the screen.
 *
 */


/* To adjust for window gravity, such as a client moving itself to the
 * southeast corner, we want to compute the gravity reference point
 * - (screen_width,screen_height) in the SE corner case - using the
 * size the client had in its configure request. But then we want
 * to compute the actual position we intend to land on using
 * the real constrained dimensions of the window.
 *
 * So for a window being placed in the SE corner and simultaneously
 * resized, we get the gravity reference point, then compute where the
 * window should go to maintain that ref. point at its current size
 * instead of at the requested size, and conceptually move the window
 * to the requested ref. point but at its current size, without
 * applying any constraints. Then we constrain it with the top and
 * left edges as the edges that vary, with a dx/dy that are the delta
 * from the current size to the requested size.
 *
 * This method applies to any ConfigureRequest that does a simultaneous
 * move/resize.
 *
 * We use the same method to e.g. maximize a window; if the window is
 * maximized, we want to MOVE_VERTICAL/MOVE_HORIZONTAL to the top
 * center of the screen, then RESIZE_BOTTOM and
 * RESIZE_HORIZONTAL_CENTER. i.e. essentially NorthGravity.
 *
 */

#define FLOOR(value, base)	( ((int) ((value) / (base))) * (base) )

typedef struct
{
  MetaWindow *window;
  MetaFrameGeometry fgeom;
  const MetaXineramaScreenInfo *xinerama;
  MetaRectangle work_area_xinerama;
  MetaRectangle work_area_screen;
  int nw_x, nw_y, se_x, se_y; /* these are whole-screen not xinerama */
} ConstraintInfo;

/* (FIXME instead of TITLEBAR_LENGTH_ONSCREEN, get the actual
 * size of the menu control?).
 */

#define TITLEBAR_LENGTH_ONSCREEN 75

typedef gboolean (* MetaConstraintAppliesFunc) (MetaWindow *window);

/* There's a function for each case with a different "free variable" */
typedef void (* MetaConstrainTopFunc)     (MetaWindow           *window,
                                           const ConstraintInfo *info,
                                           const MetaRectangle  *orig,
                                           int                  *y_delta);
typedef void (* MetaConstrainBottomFunc)  (MetaWindow           *window,
                                           const ConstraintInfo *info,
                                           const MetaRectangle  *orig,
                                           int                  *y_delta);
typedef void (* MetaConstrainVCenterFunc) (MetaWindow           *window,
                                           const ConstraintInfo *info,
                                           const MetaRectangle  *orig,
                                           int                  *y_delta);
typedef void (* MetaConstrainLeftFunc)    (MetaWindow           *window,
                                           const ConstraintInfo *info,
                                           const MetaRectangle  *orig,
                                           int                  *x_delta);
typedef void (* MetaConstrainRightFunc)   (MetaWindow           *window,
                                           const ConstraintInfo *info,
                                           const MetaRectangle  *orig,
                                           int                  *x_delta);
typedef void (* MetaConstrainHCenterFunc) (MetaWindow           *window,
                                           const ConstraintInfo *info,
                                           const MetaRectangle  *orig,
                                           int                  *x_delta);
typedef void (* MetaConstrainMoveFunc)    (MetaWindow           *window,
                                           const ConstraintInfo *info,
                                           const MetaRectangle  *orig,
                                           int                  *x_delta,
                                           int                  *y_delta);

typedef struct
{
  const char               *name;
  MetaConstraintAppliesFunc applies_func;
  MetaConstrainTopFunc      top_func;
  MetaConstrainBottomFunc   bottom_func;
  MetaConstrainVCenterFunc  vcenter_func;
  MetaConstrainLeftFunc     left_func;
  MetaConstrainRightFunc    right_func;
  MetaConstrainHCenterFunc  hcenter_func;
  MetaConstrainMoveFunc     move_func;
} Constraint;

/* "Is the desktop window" constraint:
 *
 *  new_x = 0;
 *  new_y = 0;
 *  new_w = orig_width;
 *  new_h = orig_height;
 *
 * Note that if we are applying a resize constraint,
 * e.g. constraint_desktop_top_func, this is kind of broken since we
 * end up resizing the window in order to get its position right. But
 * that case shouldn't happen in practice.
 */
static gboolean
constraint_desktop_applies_func (MetaWindow *window)
{
  return window->type == META_WINDOW_DESKTOP;
}

static void
constraint_desktop_top_func     (MetaWindow           *window,
                                 const ConstraintInfo *info,
                                 const MetaRectangle  *orig,
                                 int                  *y_delta)
{
  *y_delta = 0 - orig->y;
}

static void
constraint_desktop_bottom_func  (MetaWindow           *window,
                                 const ConstraintInfo *info,
                                 const MetaRectangle  *orig,
                                 int                  *y_delta)
{
  /* nothing */
}

static void
constraint_desktop_vcenter_func (MetaWindow           *window,
                                 const ConstraintInfo *info,
                                 const MetaRectangle  *orig,
                                 int                  *y_delta)
{
  *y_delta = 0 - orig->y;
}

static void
constraint_desktop_left_func    (MetaWindow           *window,
                                 const ConstraintInfo *info,
                                 const MetaRectangle  *orig,
                                 int                  *x_delta)
{
  *x_delta = 0 - orig->x;
}

static void
constraint_desktop_right_func   (MetaWindow           *window,
                                 const ConstraintInfo *info,
                                 const MetaRectangle  *orig,
                                 int                  *x_delta)
{
  /* nothing */
}

static void
constraint_desktop_hcenter_func (MetaWindow           *window,
                                 const ConstraintInfo *info,
                                 const MetaRectangle  *orig,
                                 int                  *x_delta)
{
  *x_delta = 0 - orig->x;
}

static void
constraint_desktop_move_func    (MetaWindow           *window,
                                 const ConstraintInfo *info,
                                 const MetaRectangle  *orig,
                                 int                  *x_delta,
                                 int                  *y_delta)
{
  *x_delta = 0 - orig->x;
  *y_delta = 0 - orig->y;
}

static const Constraint constraint_desktop = {
  "Desktop",
  constraint_desktop_applies_func,
  constraint_desktop_top_func,
  constraint_desktop_bottom_func,
  constraint_desktop_vcenter_func,
  constraint_desktop_left_func,
  constraint_desktop_right_func,
  constraint_desktop_hcenter_func,
  constraint_desktop_move_func
};

/* Titlebar is onscreen constraint:
 *
 * Constants:
 *  titlebar_width_onscreen = amount of titlebar width that has to be onscreen
 *  nw_x, nw_y = left/top edges that titlebar can't go outside
 *  se_x, se_y = right/bottom edges
 *
 * NW limit has priority over SE, since titlebar is on NW
 *
 * Left resize
 * ===
 *
 *   new_width = orig_width - dx
 *   new_x = orig_x + dx
 *
 * Amount of window+frame that doesn't fit in the work area:
 *
 *   offscreen_width = left_width + new_width + right_width - (se_x - nw_x)
 *
 * If we keep the old metacity rule where a window can be offscreen by
 * offscreen_width, then the math works out that left/top resizes are not
 * constrained. If we instead have a rule where the window can never be offscreen,
 * you get the following:
 *
 *  new_x >= nw_x + left_width + titlebar_width_offscreen
 *  orig_x + dx >= nw_x + left_width + titlebar_width_onscreen
 *  dx >= nw_x + left_width + titlebar_width_onscreen - orig_x
 *
 * i.e. the minimum dx is: nw_x + left_width + titlebar_width_onscreen - orig_x
 *
 * We could have a more complicated rule that constrains only if the current
 * offscreen width is positive, thus allowing something more like the old
 * behavior, but not doing that for now.
 *
 * Top resize works the same as left resize. Right/bottom resize don't have a limit
 * because the constraint is designed to keep the top left corner of the
 * window or its titlebar on the screen, and right/bottom resize will never move that
 * area. Center resize is almost like left/top but dx has the opposite sign
 * and new_width = orig_width + 2dx.
 *
 * For right/bottom we can try to handle windows that aren't in a valid
 * location to begin with:
 *
 *  new_x <= se_x - titlebar_width_onscreen
 *  dx <= se_x - titlebar_width_onscreen - orig_x
 *
 * but in principle this constraint is never triggered.
 *
 * Vertical move
 * ===
 *
 *  new_height = orig_height
 *  new_y = orig_y + dy
 *
 *  new_y >= nw_y + top_height
 *
 *  Min negative dy (nw_y + top_height - orig_y) just as with top resize.
 *  Max positive dy has to be computed from se_y and given less priority than the
 *  min negative:
 *
 *   new_y < se_y
 *   orig_y + dy = se_y
 *   so max dy is (se_y - orig_y)
 *
 * Horizontal move is equivalent to vertical.
 *
 */

static gboolean
constraint_onscreen_applies_func (MetaWindow *window)
{
  return
    !window->fullscreen &&
    window->type != META_WINDOW_DESKTOP &&
    window->type != META_WINDOW_DOCK;
}

static void
get_outermost_onscreen_positions (MetaWindow           *window,
                                  const ConstraintInfo *info,
                                  const MetaRectangle  *orig,
                                  int                  delta_x,
                                  int                  delta_y,
                                  int                  *leftmost_x_p,
                                  int                  *rightmost_x_p,
                                  int                  *topmost_y_p,
                                  int                  *bottommost_y_p)
{
  GList *workspaces;
  GList *tmp;
  GSList *stmp;
  MetaRectangle current;
  int bottommost_y;

  /* to handle struts, we get the list of workspaces for the window
   * and traverse all the struts in each of the cached strut lists for
   * the workspaces.  Note that because the workarea has already been
   * computed, these strut lists should already be up to date. This function
   * should have good performance since we call it a lot.
   */

  current = *orig;
  current.x += delta_x;
  current.y += delta_y;

  workspaces = meta_window_get_workspaces (window);
  tmp = workspaces;

  if (leftmost_x_p)
    {
      *leftmost_x_p = info->nw_x;
      while (tmp)
        {
          stmp = ((MetaWorkspace*) tmp->data)->left_struts;
          while (stmp)
            {
              MetaRectangle *rect = (MetaRectangle*) stmp->data;
              /* the strut only matters if the title bar is
               * overlapping the strut rect.
               */
              if (((current.y - info->fgeom.top_height >= rect->y) &&
                   (current.y - info->fgeom.top_height < rect->y + rect->height)) ||
                  ((current.y >= rect->y) &&
                   (current.y < rect->y + rect->height)))
                {
                  *leftmost_x_p = MAX (*leftmost_x_p, rect->width);
                }
              
              stmp = stmp->next;
            }
          
          tmp = tmp->next;
        }
      
      *leftmost_x_p = *leftmost_x_p - current.width + 
        MIN (TITLEBAR_LENGTH_ONSCREEN, current.width);
    }
  
  tmp = workspaces;
  if (rightmost_x_p)
    {
      *rightmost_x_p = info->se_x;
      while (tmp)
        {
          stmp = ((MetaWorkspace*) tmp->data)->right_struts;
          while (stmp)
            {
              MetaRectangle *rect = (MetaRectangle*) stmp->data;
              /* the strut only matters if the title bar is
               * overlapping the strut rect.
               */
              if (((current.y - info->fgeom.top_height >= rect->y) &&
                   (current.y - info->fgeom.top_height < rect->y + rect->height)) ||
                  ((current.y >= rect->y) &&
                   (current.y < rect->y + rect->height)))
                {
                  *rightmost_x_p = MIN (*rightmost_x_p, rect->x);
                }
              
              stmp = stmp->next;
            }
          
          tmp = tmp->next;
        }
      
      *rightmost_x_p = *rightmost_x_p - 
        MIN (TITLEBAR_LENGTH_ONSCREEN, current.width);
    }

  tmp = workspaces;
  if (topmost_y_p)
    {
      *topmost_y_p = info->nw_y;
      while (tmp)
        {
          stmp = ((MetaWorkspace*) tmp->data)->top_struts;
          while (stmp)
            {
              MetaRectangle *rect = (MetaRectangle*) stmp->data;
              /* here the strut matters if the titlebar is overlapping
               * the window horizontally
               */
              if ((current.x < rect->x + rect->width) &&
                  (current.x + current.width > rect->x))
                {
                  *topmost_y_p = MAX (*topmost_y_p, rect->height);
                }
              
              stmp = stmp->next;
            }
          
          tmp = tmp->next;
        }
      
      *topmost_y_p = *topmost_y_p + info->fgeom.top_height;
    }

  tmp = workspaces;
  bottommost_y = G_MAXUSHORT;
  if (bottommost_y_p || topmost_y_p)
    {
      bottommost_y = info->se_y;
      while (tmp)
        {
          stmp = ((MetaWorkspace*) tmp->data)->bottom_struts;
          while (stmp)
            {
              MetaRectangle *rect = (MetaRectangle*) stmp->data;
              /* here the strut matters if the titlebar is overlapping
               * the window horizontally
               */
              if ((current.x < rect->x + rect->width) &&
                  (current.x + current.width > rect->x))
                {
                  bottommost_y = MIN (bottommost_y, rect->y);
                }
              
              stmp = stmp->next;
            }
          
          tmp = tmp->next;
        }
    }

  if (bottommost_y_p)
    {
      *bottommost_y_p = bottommost_y;

      /* If no frame, keep random TITLEBAR_LENGTH_ONSCREEN pixels on the
       * screen.
       */
      if (!window->frame)
        *bottommost_y_p = *bottommost_y_p -
          MIN (TITLEBAR_LENGTH_ONSCREEN, current.height);
    }

  /* if the window has a minimum size too big for the "effective" work
   * area let it "cheat" a little by allowing a user to move it up so
   * that you can see the bottom of the window.
   */
  if (topmost_y_p)
    {
      int minheight;
      
      if (window->frame)
        {
          /* this is the "normal" case of, e.g. a dialog that's
           * just too big for the work area
           */
          minheight = window->frame->bottom_height +
            window->size_hints.min_height;
        }
      else
        {
          /* let frameless windows move offscreen is too large for the
           * effective work area.  This may include windows that try
           * to make themselves full screen by removing the
           * decorations and repositioning themselves.
           */
          minheight = orig->height;
        }
      
      if (minheight > (bottommost_y - *topmost_y_p))
          *topmost_y_p = bottommost_y - minheight;
    }
}

static void
constraint_onscreen_top_func     (MetaWindow           *window,
                                  const ConstraintInfo *info,
                                  const MetaRectangle  *orig,
                                  int                  *y_delta)
{
  int min_dy;
  int topmost_y;

  get_outermost_onscreen_positions (window, info, orig, 0, *y_delta,
                                    NULL, NULL, &topmost_y, NULL);

  min_dy = topmost_y - orig->y;

  if (*y_delta < min_dy)
    *y_delta = min_dy;
}

static void
constraint_onscreen_bottom_func  (MetaWindow           *window,
                                  const ConstraintInfo *info,
                                  const MetaRectangle  *orig,
                                  int                  *y_delta)
{
  /* no way to resize off the bottom so that constraints are
     violated */
  return;
}

static void
constraint_onscreen_vcenter_func (MetaWindow           *window,
                                  const ConstraintInfo *info,
                                  const MetaRectangle  *orig,
                                  int                  *y_delta)
{
  int max_dy;
  int topmost_y;

  get_outermost_onscreen_positions (window, info, orig, 0, *y_delta,
                                    NULL, NULL, &topmost_y, NULL);

  max_dy = orig->y - topmost_y;

  if (*y_delta > max_dy)
    *y_delta = max_dy;
}

static void
constraint_onscreen_left_func    (MetaWindow           *window,
                                  const ConstraintInfo *info,
                                  const MetaRectangle  *orig,
                                  int                  *x_delta)
{
  /* no way to resize off the sides so that constraints are violated
   */
  return;
}

static void
constraint_onscreen_right_func   (MetaWindow           *window,
                                  const ConstraintInfo *info,
                                  const MetaRectangle  *orig,
                                  int                  *x_delta)
{
  /* no way to resize off the sides so that constraints are violated
   */
  return;
}

static void
constraint_onscreen_hcenter_func (MetaWindow           *window,
                                  const ConstraintInfo *info,
                                  const MetaRectangle  *orig,
                                  int                  *x_delta)
{
  /* no way to resize off the sides so that constraints are violated
   */
  return;
}

static void
constraint_onscreen_move_func    (MetaWindow           *window,
                                  const ConstraintInfo *info,
                                  const MetaRectangle  *orig,
                                  int                  *x_delta,
                                  int                  *y_delta)
{
  int min_delta;
  int max_delta;
  int leftmost_x, rightmost_x, topmost_y, bottommost_y;

  get_outermost_onscreen_positions (window, info, orig, *x_delta, *y_delta,
                                    &leftmost_x, &rightmost_x,
                                    &topmost_y, &bottommost_y);

  min_delta = topmost_y - orig->y;
  max_delta = bottommost_y - orig->y;

  /* Note that min delta (top left) has priority over
   * max delta (bottom right) to facilitate keeping
   * titlebar on the screen
   */
  if (*y_delta > max_delta)
    *y_delta = max_delta;
  if (*y_delta < min_delta)
    *y_delta = min_delta;

  min_delta = leftmost_x - orig->x;
  max_delta = rightmost_x - orig->x;

  if (*x_delta > max_delta)
    *x_delta = max_delta;
  if (*x_delta < min_delta)
    *x_delta = min_delta;
}

static const Constraint constraint_onscreen = {
  "Onscreen",
  constraint_onscreen_applies_func,
  constraint_onscreen_top_func,
  constraint_onscreen_bottom_func,
  constraint_onscreen_vcenter_func,
  constraint_onscreen_left_func,
  constraint_onscreen_right_func,
  constraint_onscreen_hcenter_func,
  constraint_onscreen_move_func
};


/* Size hints constraints:
 *
 * For min/max size we just clamp to those, and for resize increment
 * we clamp to the one at or below the requested place.
 *
 * For aspect ratio, we special-case it at the end of
 * meta_window_constrain, because it involves both dimensions, and
 * thus messes up our generic framework.
 *
 * Left resize can be solved for dx like this:
 *   new_width = orig_width - dx
 *   new_x = orig_x + dx
 *
 *   new_width >= min_width
 *   orig_width - dx >= min_width
 *   - dx >= min_width - orig_width
 *   dx <= orig_width - min_width
 *
 *   new_width <= max_width
 *   orig_width - dx <= max_width
 *   - dx <= max_width - orig_width
 *   dx >= orig_width - max_width
 *
 */

#define USE_HINTS_FOR_WINDOW_STATE(window) (!((window)->fullscreen || (window)->maximized))

static gboolean
constraint_hints_applies_func (MetaWindow *window)
{
  return USE_HINTS_FOR_WINDOW_STATE (window);
}

static void
constraint_hints_top_func     (MetaWindow           *window,
                               const ConstraintInfo *info,
                               const MetaRectangle  *orig,
                               int                  *y_delta)
{
  int min_dy;
  int max_dy;
  int height;

  max_dy = orig->height - window->size_hints.min_height;
  min_dy = orig->height - window->size_hints.max_height;

  g_assert (max_dy >= min_dy);

  if (*y_delta > max_dy)
    *y_delta = max_dy;
  if (*y_delta < min_dy)
    *y_delta = min_dy;

  /* shrink to base + N * inc
   */
  height = orig->height - *y_delta;
  height = window->size_hints.base_height +
    FLOOR (height - window->size_hints.base_height, window->size_hints.height_inc);

  *y_delta = orig->height - height;
}

static void
constraint_hints_bottom_func  (MetaWindow           *window,
                               const ConstraintInfo *info,
                               const MetaRectangle  *orig,
                               int                  *y_delta)
{
  int min_dy;
  int max_dy;
  int height;

  min_dy = window->size_hints.min_height - orig->height;
  max_dy = window->size_hints.max_height - orig->height;

  g_assert (max_dy >= min_dy);

  if (*y_delta > max_dy)
    *y_delta = max_dy;
  if (*y_delta < min_dy)
    *y_delta = min_dy;

  /* shrink to base + N * inc
   */
  height = orig->height + *y_delta;
  height = window->size_hints.base_height +
    FLOOR (height - window->size_hints.base_height, window->size_hints.height_inc);

  *y_delta = height - orig->height;
}

static void
constraint_hints_vcenter_func (MetaWindow           *window,
                               const ConstraintInfo *info,
                               const MetaRectangle  *orig,
                               int                  *y_delta)
{
  int min_dy;
  int max_dy;
  int height;

  /* Remember our delta is negative to shrink window, positive to
   * grow it, and the actual resize is y_delta * 2 (which is broken,
   * but that's how it currently is)
   */

  min_dy = (window->size_hints.min_height - orig->height) / 2;
  max_dy = (window->size_hints.max_height - orig->height) / 2;

  g_assert (max_dy >= min_dy);

  if (*y_delta > max_dy)
    *y_delta = max_dy;
  if (*y_delta < min_dy)
    *y_delta = min_dy;

  /* shrink to base + N * inc
   */
  height = orig->height + *y_delta * 2;
  height = window->size_hints.base_height +
    FLOOR (height - window->size_hints.base_height, window->size_hints.height_inc);

  *y_delta = (height - orig->height) / 2;
}

static void
constraint_hints_left_func    (MetaWindow           *window,
                               const ConstraintInfo *info,
                               const MetaRectangle  *orig,
                               int                  *x_delta)
{
  int min_dx;
  int max_dx;
  int width;

  max_dx = orig->width - window->size_hints.min_width;
  min_dx = orig->width - window->size_hints.max_width;

  g_assert (max_dx >= min_dx);

  if (*x_delta > max_dx)
    *x_delta = max_dx;
  if (*x_delta < min_dx)
    *x_delta = min_dx;

  /* shrink to base + N * inc
   */
  width = orig->width - *x_delta;
  width = window->size_hints.base_width +
    FLOOR (width - window->size_hints.base_width, window->size_hints.width_inc);

  *x_delta = orig->width - width;
}

static void
constraint_hints_right_func   (MetaWindow           *window,
                               const ConstraintInfo *info,
                               const MetaRectangle  *orig,
                               int                  *x_delta)
{
  int min_dx;
  int max_dx;
  int width;

  min_dx = window->size_hints.min_width - orig->width;
  max_dx = window->size_hints.max_width - orig->width;

  g_assert (max_dx >= min_dx);

  if (*x_delta > max_dx)
    *x_delta = max_dx;
  if (*x_delta < min_dx)
    *x_delta = min_dx;

  /* shrink to base + N * inc
   */
  width = orig->width + *x_delta;
  width = window->size_hints.base_width +
    FLOOR (width - window->size_hints.base_width, window->size_hints.width_inc);

  *x_delta = width - orig->width;
}

static void
constraint_hints_hcenter_func (MetaWindow           *window,
                               const ConstraintInfo *info,
                               const MetaRectangle  *orig,
                               int                  *x_delta)
{
  int min_dx;
  int max_dx;
  int width;
  
  /* Remember our delta is negative to shrink window, positive to
   * grow it, and the actual resize is x_delta * 2 (which is broken,
   * but that's how it currently is)
   */

  min_dx = (window->size_hints.min_width - orig->width) / 2;
  max_dx = (window->size_hints.max_width - orig->width) / 2;

  g_assert (max_dx >= min_dx);

  if (*x_delta > max_dx)
    *x_delta = max_dx;
  if (*x_delta < min_dx)
    *x_delta = min_dx;

  /* shrink to base + N * inc
   */
  width = orig->width + *x_delta * 2;
  width = window->size_hints.base_width +
    FLOOR (width - window->size_hints.base_width, window->size_hints.width_inc);

  *x_delta = (width - orig->width) / 2;
}

static void
constraint_hints_move_func    (MetaWindow           *window,
                               const ConstraintInfo *info,
                               const MetaRectangle  *orig,
                               int                  *x_delta,
                               int                  *y_delta)
{
  /* nothing */
}

static const Constraint constraint_hints = {
  "Hints",
  constraint_hints_applies_func,
  constraint_hints_top_func,
  constraint_hints_bottom_func,
  constraint_hints_vcenter_func,
  constraint_hints_left_func,
  constraint_hints_right_func,
  constraint_hints_hcenter_func,
  constraint_hints_move_func
};

/* Array of all constraints at once */
static const Constraint *all_constraints[] = {
  &constraint_desktop,
  &constraint_onscreen,
  &constraint_hints,
  NULL
};

/* Move with no accompanying change to window size */
static void
constrain_move (MetaWindow           *window,
                const ConstraintInfo *info,
                const MetaRectangle  *orig,
                int                   x_delta,
                int                   y_delta,
                MetaRectangle        *new)
{
  const Constraint **cp;
  int old_x, old_y;
  int paranoia;

  /* Evidence that we can't actually prove this algorithm is right */
#define MAX_ITERATIONS 10
  paranoia = 0;
  
  do {
    old_x = x_delta;
    old_y = y_delta;
    cp = &all_constraints[0];

    while (*cp)
      {
        meta_topic (META_DEBUG_GEOMETRY,
                    "Before: %d %d (Move constraint '%s')\n",
                    x_delta, y_delta, (*cp)->name);

        if ((* (*cp)->applies_func) (window))
          (* (*cp)->move_func) (window, info, orig,
                                &x_delta, &y_delta);

        meta_topic (META_DEBUG_GEOMETRY,
                    "After:  %d %d (Move constraint '%s')\n",
                    x_delta, y_delta, (*cp)->name);
      
        ++cp;
      }

    ++paranoia;
  } while (((old_x != x_delta) || (old_y != y_delta)) && paranoia < MAX_ITERATIONS);

  new->x = orig->x + x_delta;
  new->y = orig->y + y_delta;

  if (paranoia >= MAX_ITERATIONS)
    meta_topic (META_DEBUG_GEOMETRY,
                "Constraints were never satisfied for window %s\n",
                window->desc);
}

static void
constrain_resize_left (MetaWindow           *window,
                       const ConstraintInfo *info,
                       const MetaRectangle  *orig,
                       int                   x_delta,
                       MetaRectangle        *new)
{
  const Constraint **cp;

  cp = &all_constraints[0];

  while (*cp)
    {
      meta_topic (META_DEBUG_GEOMETRY,
                  "Before: %d (Left constraint '%s')\n",
                  x_delta, (*cp)->name);
      
      if ((* (*cp)->applies_func) (window))
        (* (*cp)->left_func) (window, info, orig,
                              &x_delta);

      meta_topic (META_DEBUG_GEOMETRY,
                  "After:  %d (Left constraint '%s')\n",
                  x_delta, (*cp)->name);
      
      ++cp;
    }

  /* Moving mouse from 10 to 5 means current - orig means 5 - 10 means
   * a delta of -5
   */
  new->x = orig->x + x_delta;
  new->width = orig->width - x_delta;
}

static void
constrain_resize_hcenter (MetaWindow           *window,
                          const ConstraintInfo *info,
                          const MetaRectangle  *orig,
                          int                   x_delta,
                          MetaRectangle        *new)
{
  const Constraint **cp;
  
  cp = &all_constraints[0];

  while (*cp)
    {
      meta_topic (META_DEBUG_GEOMETRY,
                  "Before: %d (HCenter constraint '%s')\n",
                  x_delta, (*cp)->name);
      
      if ((* (*cp)->applies_func) (window))
        (* (*cp)->hcenter_func) (window, info, orig,
                                 &x_delta);

      meta_topic (META_DEBUG_GEOMETRY,
                  "After:  %d (HCenter constraint '%s')\n",
                  x_delta, (*cp)->name);
      
      ++cp;
    }
  
  /* center deltas are positive to grow the window and negative to
   * shrink it.
   */
  new->x = orig->x - x_delta;
  new->width = orig->width + x_delta * 2;
  /* FIXME above implies that with center gravity you have to grow
   * in increments of two
   */
}

static void
constrain_resize_right (MetaWindow           *window,
                        const ConstraintInfo *info,
                        const MetaRectangle  *orig,
                        int                   x_delta,
                        MetaRectangle        *new)
{
  const Constraint **cp;

  cp = &all_constraints[0];

  while (*cp)
    {
      meta_topic (META_DEBUG_GEOMETRY,
                  "Before: %d (Right constraint '%s')\n",
                  x_delta, (*cp)->name);
      
      if ((* (*cp)->applies_func) (window))
        (* (*cp)->right_func) (window, info, orig,
                               &x_delta);

      meta_topic (META_DEBUG_GEOMETRY,
                  "After:  %d (Right constraint '%s')\n",
                  x_delta, (*cp)->name);
      
      ++cp;
    }

  new->width = orig->width + x_delta;
}

static void
constrain_resize_top (MetaWindow           *window,
                      const ConstraintInfo *info,
                      const MetaRectangle  *orig,
                      int                   y_delta,
                      MetaRectangle        *new)
{
  const Constraint **cp;

  cp = &all_constraints[0];

  while (*cp)
    {
      meta_topic (META_DEBUG_GEOMETRY,
                  "Before: %d (Top constraint '%s')\n",
                  y_delta, (*cp)->name);
      
      if ((* (*cp)->applies_func) (window))
        (* (*cp)->top_func) (window, info, orig,
                             &y_delta);

      meta_topic (META_DEBUG_GEOMETRY,
                  "After:  %d (Top constraint '%s')\n",
                  y_delta, (*cp)->name);
      
      ++cp;
    }

  new->y = orig->y + y_delta;
  new->height = orig->height - y_delta;
}

static void
constrain_resize_vcenter (MetaWindow           *window,
                          const ConstraintInfo *info,
                          const MetaRectangle  *orig,
                          int                   y_delta,
                          MetaRectangle        *new)
{
  const Constraint **cp;

  cp = &all_constraints[0];

  while (*cp)
    {
      meta_topic (META_DEBUG_GEOMETRY,
                  "Before: %d (VCenter constraint '%s')\n",
                  y_delta, (*cp)->name);
      
      if ((* (*cp)->applies_func) (window))
        (* (*cp)->vcenter_func) (window, info, orig,
                                 &y_delta);

      meta_topic (META_DEBUG_GEOMETRY,
                  "After:  %d (VCenter constraint '%s')\n",
                  y_delta, (*cp)->name);
      
      ++cp;
    }

  /* center deltas are positive to grow the window and negative to
   * shrink it.
   */
  new->y = orig->y - y_delta;
  new->height = orig->height + y_delta * 2;
  /* FIXME above implies that with center gravity you have to grow
   * in increments of two
   */
}

static void
constrain_resize_bottom (MetaWindow           *window,
                         const ConstraintInfo *info,
                         const MetaRectangle  *orig,
                         int                   y_delta,
                         MetaRectangle        *new)
{
  const Constraint **cp;

  cp = &all_constraints[0];

  while (*cp)
    {
      meta_topic (META_DEBUG_GEOMETRY,
                  "Before: %d (Bottom constraint '%s')\n",
                  y_delta, (*cp)->name);
      
      if ((* (*cp)->applies_func) (window))
        (* (*cp)->bottom_func) (window, info, orig,
                                &y_delta);

      meta_topic (META_DEBUG_GEOMETRY,
                  "After:  %d (Bottom constraint '%s')\n",
                  y_delta, (*cp)->name);
      
      ++cp;
    }

  new->height = orig->height + y_delta;
}

static void
update_position_limits (MetaWindow          *window,
                        ConstraintInfo      *info)
{
  int nw_x, nw_y;
  int se_x, se_y;

  /* For maximized windows the limits are the work area, for
   * other windows we see which struts apply based on the
   * window's position later on
   */
  if (window->maximized)
    {
      nw_x = MIN (info->work_area_xinerama.x, info->work_area_screen.x);
      nw_y = MIN (info->work_area_xinerama.y, info->work_area_screen.y);

      /* find bottom-right corner of workarea */
      se_x = MAX (info->work_area_xinerama.x + info->work_area_xinerama.width,
		  info->work_area_screen.x + info->work_area_screen.width);
      se_y = MAX (info->work_area_xinerama.y + info->work_area_xinerama.height,
		  info->work_area_screen.y + info->work_area_screen.height);
    }
  else
    {
      nw_x = 0;
      nw_y = 0;
      se_x = window->screen->width;
      se_y = window->screen->height;
   }

  /* If we have a micro-screen or huge frames maybe nw/se got
   * swapped
   */
  if (nw_x > se_x)
    {
      int tmp = nw_x;
      nw_x = se_x;
      se_x = tmp;
    }

  if (nw_y > se_y)
    {
      int tmp = nw_y;
      nw_y = se_y;
      se_y = tmp;
    }

  info->nw_x = nw_x;
  info->nw_y = nw_y;
  info->se_x = se_x;
  info->se_y = se_y;
}

/* The delta values are the mouse motion distance deltas,
 * i.e. mouse_current_pos - mouse_orig_pos, for resizing on
 * the sides, or moving. For center resize, the delta
 * value is positive to grow the window and negative to
 * shrink it (while the sign of the mouse delta
 * depends on which side of the window you are center resizing
 * from)
 */
void
meta_window_constrain (MetaWindow          *window,
                       MetaFrameGeometry   *orig_fgeom,
                       const MetaRectangle *orig,
                       int                  x_move_delta,
                       int                  y_move_delta,
                       MetaResizeDirection  x_direction,
                       int                  x_delta,
                       MetaResizeDirection  y_direction,
                       int                  y_delta,
                       MetaRectangle       *new)
{
  ConstraintInfo info;
  MetaRectangle current;
  gboolean did_placement;

#define OUTER_WIDTH(rect) ((rect).width + info.fgeom.left_width + info.fgeom.right_width)
#define OUTER_HEIGHT(rect) ((rect).height + info.fgeom.top_height + info.fgeom.bottom_height)

  meta_topic (META_DEBUG_GEOMETRY,
              "Constraining %s x_move_delta = %d y_move_delta = %d x_direction = %d y_direction = %d x_delta = %d y_delta = %d orig %d,%d %dx%d\n",
              window->desc, x_move_delta, y_move_delta,
              x_direction, y_direction, x_delta, y_delta,
              orig->x, orig->y, orig->width, orig->height);

  /* Create a fake frame geometry if none really exists */
  if (orig_fgeom && !window->fullscreen)
    info.fgeom = *orig_fgeom;
  else
    {
      info.fgeom.top_height = 0;
      info.fgeom.bottom_height = 0;
      info.fgeom.left_width = 0;
      info.fgeom.right_width = 0;
    }

  meta_window_get_work_area_current_xinerama (window, &info.work_area_xinerama);
  meta_window_get_work_area_all_xineramas (window, &info.work_area_screen);

  info.window = window;
  info.xinerama = meta_screen_get_xinerama_for_window (window->screen,
                                                       window);
  /* Init info->nw_x etc. */
  update_position_limits (window, &info);

  current = *orig;
  *new = current;

  /* 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 &&
      !window->maximized &&
      !window->fullscreen)
    {
      MetaRectangle placed_rect = current;

      meta_window_place (window, orig_fgeom, current.x, current.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
       */
      info.xinerama = meta_screen_get_xinerama_for_rect (window->screen,
                                              &placed_rect);
      meta_window_get_work_area_for_xinerama (window,
                                              info.xinerama->number,
                                              &info.work_area_xinerama);
      update_position_limits (window, &info);

      constrain_move (window, &info, &current,
                      placed_rect.x - current.x,
                      placed_rect.y - current.y,
                      new);
      current = *new;

      /* Ignore any non-placement movement */
      x_move_delta = 0;
      y_move_delta = 0;

    }

  if (window->maximize_after_placement &&
      (window->placed || did_placement))
    {
      window->maximize_after_placement = FALSE;

      if (OUTER_WIDTH (*new) >= info.work_area_xinerama.width &&
	  OUTER_HEIGHT (*new) >= info.work_area_xinerama.height)
	{
	  /* define a sane saved_rect so that the user can unmaximize
	   * to something reasonable.
	   */
	  new->width = .75 * info.work_area_xinerama.width;
	  new->height = .75 * info.work_area_xinerama.height;
	  new->x = info.work_area_xinerama.x + .125 * info.work_area_xinerama.width;
	  new->y = info.work_area_xinerama.y + .083 * info.work_area_xinerama.height;
	}

      meta_window_maximize_internal (window, new);

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

  /* Maximization, fullscreen, etc. are defined as a resize followed by
   * a move, as explained in one of the big comments at the top of
   * this file.
   */
  if (window->fullscreen)
    {
      current = *new;
      constrain_resize_bottom (window, &info, &current,
                               (info.xinerama->height - OUTER_HEIGHT (current)),
                               new);

      current = *new;

      constrain_resize_right (window, &info, &current,
                              info.xinerama->width - OUTER_WIDTH (current),
                              new);
      current = *new;

      constrain_move (window, &info, &current,
                      info.xinerama->x_origin - current.x + info.fgeom.left_width,
                      info.xinerama->y_origin - current.y + info.fgeom.top_height,
                      new);
    }
  else if (window->maximized)
    {
      constrain_resize_bottom (window, &info, &current,
                               (info.work_area_xinerama.height - OUTER_HEIGHT (current)),
                               new);

      current = *new;

      constrain_resize_right (window, &info, &current,
                              info.work_area_xinerama.width - OUTER_WIDTH (current),
                              new);
      current = *new;

      constrain_move (window, &info, &current,
                      info.work_area_xinerama.x - current.x + info.fgeom.left_width,
                      info.work_area_xinerama.y - current.y + info.fgeom.top_height,
                      new);

      current = *new;
    }
  else
    {
      switch (x_direction)
        {
        case META_RESIZE_LEFT_OR_TOP:
          constrain_resize_left (window, &info, &current,
                                 x_delta, new);
          break;
        case META_RESIZE_CENTER:
          constrain_resize_hcenter (window, &info, &current,
                                    x_delta, new);
          break;
        case META_RESIZE_RIGHT_OR_BOTTOM:
          constrain_resize_right (window, &info, &current,
                                  x_delta, new);
          break;
        }

      switch (y_direction)
        {
        case META_RESIZE_LEFT_OR_TOP:
          constrain_resize_top (window, &info, &current,
                                y_delta, new);
          break;
        case META_RESIZE_CENTER:
          constrain_resize_vcenter (window, &info, &current,
                                    y_delta, new);
          break;
        case META_RESIZE_RIGHT_OR_BOTTOM:
          constrain_resize_bottom (window, &info, &current,
                                   y_delta, new);
          break;
        }

      current = *new;

      constrain_move (window, &info, &current,
                      x_move_delta, y_move_delta,
                      new);

      current = *new;
    }

  /* Now we have to sort out the aspect ratio */
  if (!window->fullscreen)
    {
      /*
       *                width
       * min_aspect <= -------- <= max_aspect
       *                height
       */
      double min_aspect, max_aspect;
      int width, height;
      
      min_aspect = window->size_hints.min_aspect.x / (double) window->size_hints.min_aspect.y;
      max_aspect = window->size_hints.max_aspect.x / (double) window->size_hints.max_aspect.y;
      
      width = current.width;
      height = current.height;

      if (min_aspect * height > width)
        {
          int delta;
          
          if (y_direction == META_RESIZE_CENTER)
            {
              delta = FLOOR (height * min_aspect - width, window->size_hints.width_inc);
              if (width + delta <= window->size_hints.max_width)
                width += delta;
              else
                {
                  delta = FLOOR (height - width / min_aspect, window->size_hints.height_inc);
                  if (height - delta >= window->size_hints.min_height)
                    height -= delta;
                }
            }
          else
            {
              delta = FLOOR (height - width / min_aspect, window->size_hints.height_inc);
              if (height - delta >= window->size_hints.min_height)
                height -= delta;
              else
                {
                  delta = FLOOR (height * min_aspect - width, window->size_hints.width_inc);
                  if (width + delta <= window->size_hints.max_width)
                    width += delta;
                }
            }
        }
      
      if (max_aspect * height < width)
        {
          int delta;
          
          if (x_direction == META_RESIZE_CENTER)
            {
              delta = FLOOR (width / max_aspect - height, window->size_hints.height_inc);
              if (height + delta <= window->size_hints.max_height)
                height += delta;
              else
                {
                  delta = FLOOR (width - height * max_aspect, window->size_hints.width_inc);
                  if (width - delta >= window->size_hints.min_width)
                    width -= delta;
                }
            }
          else
            {
              delta = FLOOR (width - height * max_aspect, window->size_hints.width_inc);
              if (width - delta >= window->size_hints.min_width)
                width -= delta;
              else
                {
                  delta = FLOOR (width / max_aspect - height, window->size_hints.height_inc);
                  if (height + delta <= window->size_hints.max_height)
                    height += delta;
                }
            }
        }
      
      /* Convert into terms of the direction of resize and reapply the
       * earlier constraints; this means aspect ratio becomes the
       * least-important of the constraints. If we wanted aspect to be
       * the most important, we could just not do this next bit.
       */
      
      if (current.width != width)
        {
          x_delta = width - current.width; /* positive delta to increase width */
          switch (x_direction)
            {
            case META_RESIZE_LEFT_OR_TOP:
              constrain_resize_left (window, &info, &current,
                                     - x_delta, new);
              break;
            case META_RESIZE_CENTER:
              constrain_resize_hcenter (window, &info, &current,
                                        x_delta, new);
              break;
            case META_RESIZE_RIGHT_OR_BOTTOM:
              constrain_resize_right (window, &info, &current,
                                      x_delta, new);
              break;
            }
        }
      
      if (current.height != height)
        {
          y_delta = height - current.height; /* positive to increase height */
          
          switch (y_direction)
            {
            case META_RESIZE_LEFT_OR_TOP:
              constrain_resize_top (window, &info, &current,
                                    - y_delta, new);
              break;
            case META_RESIZE_CENTER:
              constrain_resize_vcenter (window, &info, &current,
                                        y_delta, new);
              break;
            case META_RESIZE_RIGHT_OR_BOTTOM:
              constrain_resize_bottom (window, &info, &current,
                                       y_delta, new);
              break;
            }
        }
      
      current = *new;
    }

  meta_topic (META_DEBUG_GEOMETRY,
              "Constrained %s new %d,%d %dx%d old %d,%d %dx%d\n",
              window->desc,
              new->x, new->y, new->width, new->height,
              orig->x, orig->y, orig->width, orig->height);
}

MetaResizeDirection
meta_x_direction_from_gravity (int gravity)
{
  switch (gravity)
    {
    case EastGravity:
    case NorthEastGravity:
    case SouthEastGravity:
      return META_RESIZE_LEFT_OR_TOP;
      break;

    case WestGravity:
    case NorthWestGravity:
    case SouthWestGravity:
    case StaticGravity:
      return META_RESIZE_RIGHT_OR_BOTTOM;
      break;

    default:
      return META_RESIZE_CENTER;
      break;
    }
}

MetaResizeDirection
meta_y_direction_from_gravity (int gravity)
{
  switch (gravity)
    {
    case SouthGravity:
    case SouthWestGravity:
    case SouthEastGravity:
      return META_RESIZE_LEFT_OR_TOP;
      break;

    case NorthGravity:
    case NorthWestGravity:
    case NorthEastGravity:
    case StaticGravity:
      return META_RESIZE_RIGHT_OR_BOTTOM;
      break;

    default:
      return META_RESIZE_CENTER;
    }
}