path: root/gtk/gtksizerequest.c

/* gtksizerequest.c
 * Copyright (C) 2007-2010 Openismus GmbH
 *
 * Authors:
 *      Mathias Hasselmann <mathias@openismus.com>
 *      Tristan Van Berkom <tristan.van.berkom@gmail.com>
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Library General Public
 * License as published by the Free Software Foundation; either
 * version 2 of the License, or (at your option) any later version.
 *
 * This library 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
 * Library General Public License for more details.
 *
 * You should have received a copy of the GNU Library General Public
 * License along with this library. If not, see <http://www.gnu.org/licenses/>.
 */

#include <config.h>

#include "gtksizerequest.h"

#include "gtkdebug.h"
#include "gtkintl.h"
#include "gtkprivate.h"
#include "gtksizegroup-private.h"
#include "gtkwidgetprivate.h"
#include "deprecated/gtkstyle.h"


#ifndef G_DISABLE_CHECKS
static GQuark recursion_check_quark = 0;
#endif /* G_DISABLE_CHECKS */

static void
push_recursion_check (GtkWidget       *widget,
                      GtkSizeGroupMode orientation,
                      gint             for_size)
{
#ifndef G_DISABLE_CHECKS
  const char *previous_method;
  const char *method;

  if (recursion_check_quark == 0)
    recursion_check_quark = g_quark_from_static_string ("gtk-size-request-in-progress");

  previous_method = g_object_get_qdata (G_OBJECT (widget), recursion_check_quark);

  if (orientation == GTK_SIZE_GROUP_HORIZONTAL)
    {
      method = for_size < 0 ? "get_width" : "get_width_for_height";
    }
  else
    {
      method = for_size < 0 ? "get_height" : "get_height_for_width";
    }

  if (previous_method != NULL)
    {
      g_warning ("%s %p: widget tried to gtk_widget_%s inside "
                 " GtkWidget     ::%s implementation. "
                 "Should just invoke GTK_WIDGET_GET_CLASS(widget)->%s "
                 "directly rather than using gtk_widget_%s",
                 G_OBJECT_TYPE_NAME (widget), widget,
                 method, previous_method,
                 method, method);
    }

  g_object_set_qdata (G_OBJECT (widget), recursion_check_quark, (char*) method);
#endif /* G_DISABLE_CHECKS */
}

static void
pop_recursion_check (GtkWidget       *widget,
                     GtkSizeGroupMode orientation)
{
#ifndef G_DISABLE_CHECKS
  g_object_set_qdata (G_OBJECT (widget), recursion_check_quark, NULL);
#endif
}


static void
clear_cache (SizeRequestCache   *cache,
	     GtkSizeGroupMode    orientation)
{
  SizeRequest **sizes;
  gint          i;

  if (orientation == GTK_SIZE_GROUP_HORIZONTAL)
    {
      sizes = cache->widths;

      cache->widths            = NULL;
      cache->cached_widths     = 0;
      cache->last_cached_width = 0;
      cache->cached_base_width = FALSE;
    }
  else
    {
      sizes = cache->heights;

      cache->heights            = NULL;
      cache->cached_heights     = 0;
      cache->last_cached_height = 0; 
      cache->cached_base_height = FALSE;
   }

  if (sizes)
    {
      for (i = 0; i < GTK_SIZE_REQUEST_CACHED_SIZES && sizes[i] != NULL; i++)
	g_slice_free (SizeRequest, sizes[i]);
      
      g_slice_free1 (sizeof (SizeRequest *) * GTK_SIZE_REQUEST_CACHED_SIZES, sizes);
    }
}

void
_gtk_widget_free_cached_sizes (GtkWidget *widget)
{
  SizeRequestCache   *cache;

  cache = _gtk_widget_peek_request_cache (widget);

  clear_cache (cache, GTK_SIZE_GROUP_HORIZONTAL);
  clear_cache (cache, GTK_SIZE_GROUP_VERTICAL);
}

/* This function checks if 'request_needed' flag is present
 * and resets the cache state if a request is needed for
 * a given orientation.
 */
static SizeRequestCache *
init_cache (GtkWidget        *widget)
{
  SizeRequestCache *cache;

  cache = _gtk_widget_peek_request_cache (widget);

  if (_gtk_widget_get_width_request_needed (widget))
    clear_cache (cache, GTK_SIZE_GROUP_HORIZONTAL);
  
  if (_gtk_widget_get_height_request_needed (widget))
    clear_cache (cache, GTK_SIZE_GROUP_VERTICAL);

  return cache;
}

/* looks for a cached size request for this for_size. If not
 * found, returns the oldest entry so it can be overwritten
 *
 * Note that this caching code was originally derived from
 * the Clutter toolkit but has evolved for other GTK+ requirements.
 */
static gboolean
get_cached_size (GtkWidget         *widget,
		 GtkSizeGroupMode   orientation,
		 gint               for_size,
		 CachedSize       **result)
{
  SizeRequestCache  *cache;
  SizeRequest      **cached_sizes;
  guint              i, n_sizes;

  cache = init_cache (widget);

  if (for_size < 0)
    {
      if (orientation == GTK_SIZE_GROUP_HORIZONTAL)
	{
	  *result = &cache->cached_width;
	  return cache->cached_base_width;
	}
      else
	{
	  *result = &cache->cached_height;
	  return cache->cached_base_height;
	}
    }

  if (orientation == GTK_SIZE_GROUP_HORIZONTAL)
    {
      cached_sizes = cache->widths;
      n_sizes      = cache->cached_widths;
    }
  else
    {
      cached_sizes = cache->heights;
      n_sizes      = cache->cached_heights;
    }

  /* Search for an already cached size */
  for (i = 0; i < n_sizes; i++)
    {
      if (cached_sizes[i]->lower_for_size <= for_size &&
	  cached_sizes[i]->upper_for_size >= for_size)
	{
	  *result = &cached_sizes[i]->cached_size;
	  return TRUE;
	}
    }

  return FALSE;
}

static void
commit_cached_size (GtkWidget         *widget,
		    GtkSizeGroupMode   orientation,
		    gint               for_size,
		    gint               minimum_size,
		    gint               natural_size)
{
  SizeRequestCache  *cache;
  SizeRequest      **cached_sizes;
  guint              i, n_sizes;

  cache = _gtk_widget_peek_request_cache (widget);

  /* First handle caching of the base requests */
  if (for_size < 0)
    {
      if (orientation == GTK_SIZE_GROUP_HORIZONTAL)
	{
	  cache->cached_width.minimum_size = minimum_size;
	  cache->cached_width.natural_size = natural_size;
	  cache->cached_base_width = TRUE;
	}
      else
	{
	  cache->cached_height.minimum_size = minimum_size;
	  cache->cached_height.natural_size = natural_size;
	  cache->cached_base_height = TRUE;
	}
      return;
    }

  /* Check if the minimum_size and natural_size is already
   * in the cache and if this result can be used to extend
   * that cache entry 
   */
  if (orientation == GTK_SIZE_GROUP_HORIZONTAL)
    {
      cached_sizes = cache->widths;
      n_sizes = cache->cached_widths;
    }
  else
    {
      cached_sizes = cache->heights;
      n_sizes = cache->cached_heights;
    }

  for (i = 0; i < n_sizes; i++)
    {
      if (cached_sizes[i]->cached_size.minimum_size == minimum_size &&
	  cached_sizes[i]->cached_size.natural_size == natural_size)
	{
	  cached_sizes[i]->lower_for_size = MIN (cached_sizes[i]->lower_for_size, for_size);
	  cached_sizes[i]->upper_for_size = MAX (cached_sizes[i]->upper_for_size, for_size);
	  return;
	}
    }

  /* If not found, pull a new size from the cache, the returned size cache
   * will immediately be used to cache the new computed size so we go ahead
   * and increment the last_cached_width/height right away */
  if (orientation == GTK_SIZE_GROUP_HORIZONTAL)
    {
      if (cache->cached_widths < GTK_SIZE_REQUEST_CACHED_SIZES)
	{
	  cache->cached_widths++;
	  cache->last_cached_width = cache->cached_widths - 1;
	}
      else
	{
	  if (++cache->last_cached_width == GTK_SIZE_REQUEST_CACHED_SIZES)
	    cache->last_cached_width = 0;
	}

      if (!cache->widths)
	cache->widths = g_slice_alloc0 (sizeof (SizeRequest *) * GTK_SIZE_REQUEST_CACHED_SIZES);

      if (!cache->widths[cache->last_cached_width])
	cache->widths[cache->last_cached_width] = g_slice_new (SizeRequest);

      cache->widths[cache->last_cached_width]->lower_for_size = for_size;
      cache->widths[cache->last_cached_width]->upper_for_size = for_size;
      cache->widths[cache->last_cached_width]->cached_size.minimum_size = minimum_size;
      cache->widths[cache->last_cached_width]->cached_size.natural_size = natural_size;
    }
  else /* GTK_SIZE_GROUP_VERTICAL */
    {
      if (cache->cached_heights < GTK_SIZE_REQUEST_CACHED_SIZES)
	{
	  cache->cached_heights++;
	  cache->last_cached_height = cache->cached_heights - 1;
	}
      else
	{
	  if (++cache->last_cached_height == GTK_SIZE_REQUEST_CACHED_SIZES)
	    cache->last_cached_height = 0;
	}

      if (!cache->heights)
	cache->heights = g_slice_alloc0 (sizeof (SizeRequest *) * GTK_SIZE_REQUEST_CACHED_SIZES);

      if (!cache->heights[cache->last_cached_height])
	cache->heights[cache->last_cached_height] = g_slice_new (SizeRequest);

      cache->heights[cache->last_cached_height]->lower_for_size = for_size;
      cache->heights[cache->last_cached_height]->upper_for_size = for_size;
      cache->heights[cache->last_cached_height]->cached_size.minimum_size = minimum_size;
      cache->heights[cache->last_cached_height]->cached_size.natural_size = natural_size;
    }
}

static const char *
get_vfunc_name (GtkSizeGroupMode orientation,
                gint             for_size)
{
  if (orientation == GTK_SIZE_GROUP_HORIZONTAL)
    return for_size < 0 ? "get_preferred_width" : "get_preferred_width_for_height";
  else
    return for_size < 0 ? "get_preferred_height" : "get_preferred_height_for_width";
}

/* This is the main function that checks for a cached size and
 * possibly queries the widget class to compute the size if it's
 * not cached. If the for_size here is -1, then get_preferred_width()
 * or get_preferred_height() will be used.
 */
static void
compute_size_for_orientation (GtkWidget         *widget,
                              GtkSizeGroupMode   orientation,
                              gint               for_size,
                              gint              *minimum_size,
                              gint              *natural_size)
{
  CachedSize       *cached_size;
  gboolean          found_in_cache = FALSE;
  gint              min_size = 0;
  gint              nat_size = 0;

  found_in_cache = get_cached_size (widget, orientation, for_size, &cached_size);

  if (!found_in_cache)
    {
      gint adjusted_min, adjusted_natural, adjusted_for_size = for_size;

      gtk_widget_ensure_style (widget);

      if (orientation == GTK_SIZE_GROUP_HORIZONTAL)
        {
          if (for_size < 0)
            {
	      push_recursion_check (widget, orientation, for_size);
              GTK_WIDGET_GET_CLASS (widget)->get_preferred_width (widget, &min_size, &nat_size);
	      pop_recursion_check (widget, orientation);
            }
          else
            {
              gint ignored_position = 0;
              gint minimum_height;
              gint natural_height;

	      /* Pull the base natural height from the cache as it's needed to adjust
	       * the proposed 'for_size' */
	      gtk_widget_get_preferred_height (widget, &minimum_height, &natural_height);

              /* convert for_size to unadjusted height (for_size is a proposed allocation) */
              GTK_WIDGET_GET_CLASS (widget)->adjust_size_allocation (widget,
                                                                     GTK_ORIENTATION_VERTICAL,
                                                                     &minimum_height,
								     &natural_height,
                                                                     &ignored_position,
                                                                     &adjusted_for_size);

	      push_recursion_check (widget, orientation, for_size);
              GTK_WIDGET_GET_CLASS (widget)->get_preferred_width_for_height (widget, 
									     MAX (adjusted_for_size, minimum_height),
									     &min_size, &nat_size);
	      pop_recursion_check (widget, orientation);
            }
        }
      else
        {
          if (for_size < 0)
            {
	      push_recursion_check (widget, orientation, for_size);
              GTK_WIDGET_GET_CLASS (widget)->get_preferred_height (widget, &min_size, &nat_size);
	      pop_recursion_check (widget, orientation);
            }
          else
            {
              gint ignored_position = 0;
              gint minimum_width;
              gint natural_width;

	      /* Pull the base natural width from the cache as it's needed to adjust
	       * the proposed 'for_size' */
	      gtk_widget_get_preferred_width (widget, &minimum_width, &natural_width);

              /* convert for_size to unadjusted width (for_size is a proposed allocation) */
              GTK_WIDGET_GET_CLASS (widget)->adjust_size_allocation (widget,
                                                                     GTK_ORIENTATION_HORIZONTAL,
								     &minimum_width,
                                                                     &natural_width,
                                                                     &ignored_position,
                                                                     &adjusted_for_size);

	      push_recursion_check (widget, orientation, for_size);
              GTK_WIDGET_GET_CLASS (widget)->get_preferred_height_for_width (widget, 
									     MAX (adjusted_for_size, minimum_width),
									     &min_size, &nat_size);
	      pop_recursion_check (widget, orientation);
            }
        }

      if (min_size > nat_size)
        {
          g_warning ("%s %p reported min size %d and natural size %d in %s(); natural size must be >= min size",
                     G_OBJECT_TYPE_NAME (widget), widget, min_size, nat_size, get_vfunc_name (orientation, for_size));
        }

      if (orientation == GTK_SIZE_GROUP_HORIZONTAL)
          _gtk_widget_set_width_request_needed (widget, FALSE);
      else
          _gtk_widget_set_height_request_needed (widget, FALSE);

      adjusted_min     = min_size;
      adjusted_natural = nat_size;
      GTK_WIDGET_GET_CLASS (widget)->adjust_size_request (widget,
                                                          orientation == GTK_SIZE_GROUP_HORIZONTAL ?
                                                          GTK_ORIENTATION_HORIZONTAL :
                                                          GTK_ORIENTATION_VERTICAL,
                                                          &adjusted_min,
                                                          &adjusted_natural);

      if (adjusted_min < min_size ||
          adjusted_natural < nat_size)
        {
          g_warning ("%s %p adjusted size %s min %d natural %d must not decrease below min %d natural %d",
                     G_OBJECT_TYPE_NAME (widget), widget,
                     orientation == GTK_SIZE_GROUP_VERTICAL ? "vertical" : "horizontal",
                     adjusted_min, adjusted_natural,
                     min_size, nat_size);
          /* don't use the adjustment */
        }
      else if (adjusted_min > adjusted_natural)
        {
          g_warning ("%s %p adjusted size %s min %d natural %d original min %d natural %d has min greater than natural",
                     G_OBJECT_TYPE_NAME (widget), widget,
                     orientation == GTK_SIZE_GROUP_VERTICAL ? "vertical" : "horizontal",
                     adjusted_min, adjusted_natural,
                     min_size, nat_size);
          /* don't use the adjustment */
        }
      else
        {
          /* adjustment looks good */
          min_size = adjusted_min;
          nat_size = adjusted_natural;
        }

      /* Update size-groups with our request and update our cached requests
       * with the size-group values in a single pass.
       */
      _gtk_size_group_bump_requisition (widget,
					orientation,
                                        for_size,
					&min_size,
					&nat_size);

      commit_cached_size (widget, orientation, for_size, min_size, nat_size);
    }
  else
    {
      min_size = cached_size->minimum_size;
      nat_size = cached_size->natural_size;
    }

  if (minimum_size)
    *minimum_size = min_size;

  if (natural_size)
    *natural_size = nat_size;

  g_assert (min_size <= nat_size);

  GTK_NOTE (SIZE_REQUEST,
            g_print ("[%p] %s\t%s: %d is minimum %d and natural: %d (hit cache: %s)\n",
                     widget, G_OBJECT_TYPE_NAME (widget),
                     orientation == GTK_SIZE_GROUP_HORIZONTAL ?
                     "width for height" : "height for width" ,
                     for_size, min_size, nat_size,
                     found_in_cache ? "yes" : "no"));

}

/**
 * gtk_widget_get_request_mode:
 * @widget: a #GtkWidget instance
 *
 * Gets whether the widget prefers a height-for-width layout
 * or a width-for-height layout.
 *
 * <note><para>#GtkBin widgets generally propagate the preference of
 * their child, container widgets need to request something either in
 * context of their children or in context of their allocation
 * capabilities.</para></note>
 *
 * Returns: The #GtkSizeRequestMode preferred by @widget.
 *
 * Since: 3.0
 */
GtkSizeRequestMode
gtk_widget_get_request_mode (GtkWidget *widget)
{
  g_return_val_if_fail (GTK_IS_WIDGET (widget), GTK_SIZE_REQUEST_CONSTANT_SIZE);

  return GTK_WIDGET_GET_CLASS (widget)->get_request_mode (widget);
}

/**
 * gtk_widget_get_preferred_width:
 * @widget: a #GtkWidget instance
 * @minimum_width: (out) (allow-none): location to store the minimum width, or %NULL
 * @natural_width: (out) (allow-none): location to store the natural width, or %NULL
 *
 * Retrieves a widget's initial minimum and natural width.
 *
 * <note><para>This call is specific to height-for-width
 * requests.</para></note>
 *
 * The returned request will be modified by the
 * GtkWidgetClass::adjust_size_request virtual method and by any
 * #GtkSizeGroup<!-- -->s that have been applied. That is, the returned request
 * is the one that should be used for layout, not necessarily the one
 * returned by the widget itself.
 *
 * Since: 3.0
 */
void
gtk_widget_get_preferred_width (GtkWidget *widget,
                                gint      *minimum_width,
                                gint      *natural_width)
{
  g_return_if_fail (GTK_IS_WIDGET (widget));
  g_return_if_fail (minimum_width != NULL || natural_width != NULL);

  compute_size_for_orientation (widget, GTK_SIZE_GROUP_HORIZONTAL,
                                -1, minimum_width, natural_width);
}


/**
 * gtk_widget_get_preferred_height:
 * @widget: a #GtkWidget instance
 * @minimum_height: (out) (allow-none): location to store the minimum height, or %NULL
 * @natural_height: (out) (allow-none): location to store the natural height, or %NULL
 *
 * Retrieves a widget's initial minimum and natural height.
 *
 * <note><para>This call is specific to width-for-height requests.</para></note>
 *
 * The returned request will be modified by the
 * GtkWidgetClass::adjust_size_request virtual method and by any
 * #GtkSizeGroup<!-- -->s that have been applied. That is, the returned request
 * is the one that should be used for layout, not necessarily the one
 * returned by the widget itself.
 *
 * Since: 3.0
 */
void
gtk_widget_get_preferred_height (GtkWidget *widget,
                                 gint      *minimum_height,
                                 gint      *natural_height)
{
  g_return_if_fail (GTK_IS_WIDGET (widget));
  g_return_if_fail (minimum_height != NULL || natural_height != NULL);

  compute_size_for_orientation (widget, GTK_SIZE_GROUP_VERTICAL,
                                -1, minimum_height, natural_height);
}



/**
 * gtk_widget_get_preferred_width_for_height:
 * @widget: a #GtkWidget instance
 * @height: the height which is available for allocation
 * @minimum_width: (out) (allow-none): location for storing the minimum width, or %NULL
 * @natural_width: (out) (allow-none): location for storing the natural width, or %NULL
 *
 * Retrieves a widget's minimum and natural width if it would be given
 * the specified @height.
 *
 * The returned request will be modified by the
 * GtkWidgetClass::adjust_size_request virtual method and by any
 * #GtkSizeGroup<!-- -->s that have been applied. That is, the returned request
 * is the one that should be used for layout, not necessarily the one
 * returned by the widget itself.
 *
 * Since: 3.0
 */
void
gtk_widget_get_preferred_width_for_height (GtkWidget *widget,
                                           gint       height,
                                           gint      *minimum_width,
                                           gint      *natural_width)
{
  g_return_if_fail (GTK_IS_WIDGET (widget));
  g_return_if_fail (minimum_width != NULL || natural_width != NULL);
  g_return_if_fail (height >= 0);

  if (GTK_WIDGET_GET_CLASS (widget)->get_request_mode (widget) == GTK_SIZE_REQUEST_CONSTANT_SIZE)
    compute_size_for_orientation (widget, GTK_SIZE_GROUP_HORIZONTAL,
				  -1, minimum_width, natural_width);
  else
    compute_size_for_orientation (widget, GTK_SIZE_GROUP_HORIZONTAL,
				  height, minimum_width, natural_width);
}

/**
 * gtk_widget_get_preferred_height_for_width:
 * @widget: a #GtkWidget instance
 * @width: the width which is available for allocation
 * @minimum_height: (out) (allow-none): location for storing the minimum height, or %NULL
 * @natural_height: (out) (allow-none): location for storing the natural height, or %NULL
 *
 * Retrieves a widget's minimum and natural height if it would be given
 * the specified @width.
 *
 * The returned request will be modified by the
 * GtkWidgetClass::adjust_size_request virtual method and by any
 * #GtkSizeGroup<!-- -->s that have been applied. That is, the returned request
 * is the one that should be used for layout, not necessarily the one
 * returned by the widget itself.
 *
 * Since: 3.0
 */
void
gtk_widget_get_preferred_height_for_width (GtkWidget *widget,
                                           gint       width,
                                           gint      *minimum_height,
                                           gint      *natural_height)
{
  g_return_if_fail (GTK_IS_WIDGET (widget));
  g_return_if_fail (minimum_height != NULL || natural_height != NULL);
  g_return_if_fail (width >= 0);

  if (GTK_WIDGET_GET_CLASS (widget)->get_request_mode (widget) == GTK_SIZE_REQUEST_CONSTANT_SIZE)
    compute_size_for_orientation (widget, GTK_SIZE_GROUP_VERTICAL,
				  -1, minimum_height, natural_height);
  else
    compute_size_for_orientation (widget, GTK_SIZE_GROUP_VERTICAL,
				  width, minimum_height, natural_height);
}

/**
 * gtk_widget_get_preferred_size:
 * @widget: a #GtkWidget instance
 * @minimum_size: (out) (allow-none): location for storing the minimum size, or %NULL
 * @natural_size: (out) (allow-none): location for storing the natural size, or %NULL
 *
 * Retrieves the minimum and natural size of a widget, taking
 * into account the widget's preference for height-for-width management.
 *
 * This is used to retrieve a suitable size by container widgets which do
 * not impose any restrictions on the child placement. It can be used
 * to deduce toplevel window and menu sizes as well as child widgets in
 * free-form containers such as GtkLayout.
 *
 * <note><para>Handle with care. Note that the natural height of a height-for-width
 * widget will generally be a smaller size than the minimum height, since the required
 * height for the natural width is generally smaller than the required height for
 * the minimum width.</para></note>
 *
 * Since: 3.0
 */
void
gtk_widget_get_preferred_size (GtkWidget      *widget,
                               GtkRequisition *minimum_size,
                               GtkRequisition *natural_size)
{
  gint min_width, nat_width;
  gint min_height, nat_height;

  g_return_if_fail (GTK_IS_WIDGET (widget));

  if (gtk_widget_get_request_mode (widget) == GTK_SIZE_REQUEST_HEIGHT_FOR_WIDTH)
    {
      gtk_widget_get_preferred_width (widget, &min_width, &nat_width);

      if (minimum_size)
	{
	  minimum_size->width = min_width;
	  gtk_widget_get_preferred_height_for_width (widget, min_width,
                                                     &minimum_size->height, NULL);
	}

      if (natural_size)
	{
	  natural_size->width = nat_width;
	  gtk_widget_get_preferred_height_for_width (widget, nat_width,
                                                     NULL, &natural_size->height);
	}
    }
  else /* GTK_SIZE_REQUEST_WIDTH_FOR_HEIGHT or CONSTANT_SIZE */
    {
      gtk_widget_get_preferred_height (widget, &min_height, &nat_height);

      if (minimum_size)
	{
	  minimum_size->height = min_height;
	  gtk_widget_get_preferred_width_for_height (widget, min_height,
                                                     &minimum_size->width, NULL);
	}

      if (natural_size)
	{
	  natural_size->height = nat_height;
	  gtk_widget_get_preferred_width_for_height (widget, nat_height,
                                                     NULL, &natural_size->width);
	}
    }
}


static gint
compare_gap (gconstpointer p1,
	     gconstpointer p2,
	     gpointer      data)
{
  GtkRequestedSize *sizes = data;
  const guint *c1 = p1;
  const guint *c2 = p2;

  const gint d1 = MAX (sizes[*c1].natural_size -
                       sizes[*c1].minimum_size,
                       0);
  const gint d2 = MAX (sizes[*c2].natural_size -
                       sizes[*c2].minimum_size,
                       0);

  gint delta = (d2 - d1);

  if (0 == delta)
    delta = (*c2 - *c1);

  return delta;
}

/**
 * gtk_distribute_natural_allocation:
 * @extra_space: Extra space to redistribute among children after subtracting
 *               minimum sizes and any child padding from the overall allocation
 * @n_requested_sizes: Number of requests to fit into the allocation
 * @sizes: An array of structs with a client pointer and a minimum/natural size
 *         in the orientation of the allocation.
 *
 * Distributes @extra_space to child @sizes by bringing smaller
 * children up to natural size first.
 *
 * The remaining space will be added to the @minimum_size member of the
 * GtkRequestedSize struct. If all sizes reach their natural size then
 * the remaining space is returned.
 *
 * Returns: The remainder of @extra_space after redistributing space
 * to @sizes.
 */
gint
gtk_distribute_natural_allocation (gint              extra_space,
				   guint             n_requested_sizes,
				   GtkRequestedSize *sizes)
{
  guint *spreading;
  gint   i;

  g_return_val_if_fail (extra_space >= 0, 0);

  spreading = g_newa (guint, n_requested_sizes);

  for (i = 0; i < n_requested_sizes; i++)
    spreading[i] = i;

  /* Distribute the container's extra space c_gap. We want to assign
   * this space such that the sum of extra space assigned to children
   * (c^i_gap) is equal to c_cap. The case that there's not enough
   * space for all children to take their natural size needs some
   * attention. The goals we want to achieve are:
   *
   *   a) Maximize number of children taking their natural size.
   *   b) The allocated size of children should be a continuous
   *   function of c_gap.  That is, increasing the container size by
   *   one pixel should never make drastic changes in the distribution.
   *   c) If child i takes its natural size and child j doesn't,
   *   child j should have received at least as much gap as child i.
   *
   * The following code distributes the additional space by following
   * these rules.
   */

  /* Sort descending by gap and position. */
  g_qsort_with_data (spreading,
		     n_requested_sizes, sizeof (guint),
		     compare_gap, sizes);

  /* Distribute available space.
   * This master piece of a loop was conceived by Behdad Esfahbod.
   */
  for (i = n_requested_sizes - 1; extra_space > 0 && i >= 0; --i)
    {
      /* Divide remaining space by number of remaining children.
       * Sort order and reducing remaining space by assigned space
       * ensures that space is distributed equally.
       */
      gint glue = (extra_space + i) / (i + 1);
      gint gap = sizes[(spreading[i])].natural_size
	- sizes[(spreading[i])].minimum_size;

      gint extra = MIN (glue, gap);

      sizes[spreading[i]].minimum_size += extra;

      extra_space -= extra;
    }

  return extra_space;
}