Allow StBoxLayout to shrink down to its minimum size

When a StBoxLayout is allocated a size less than its natural size,
think "shrink" needs to be divided among the children that have
a smaller minimum size than natural size.

This is done by preferentially shrinking the children that are most
expanded from their minimum size and then increasing that set of
children until we've found enough total shrink.

A new method is used of allocating children at integral sizes - instead
of rounding the per-child extra amount to an integer (which causes
cumulative round-off errors), compute the position as we go along in
floats and round individually for each child widget.

Extend the box-layout test to include of a test of a box being set
to various widths, starting quite narrow.

http://bugzilla.moblin.org/show_bug.cgi?id=6311
https://bugzilla.gnome.org/show_bug.cgi?id=595995

src/st/st-box-layout.c

@@ -34,6 +34,8 @@
  *
  */
 
+#include <stdlib.h>
+
 #include "st-box-layout.h"
 
 #include "st-private.h"
@@ -571,6 +573,125 @@ st_box_layout_get_preferred_height (ClutterActor *actor,
                                          min_height_p, natural_height_p);
 }
 
+typedef struct {
+  int child_index;
+  gfloat shrink_amount;
+} BoxChildShrink;
+
+/* Sort with the greatest shrink amount first */
+static int
+compare_by_shrink_amount (const void *a,
+                          const void *b)
+{
+  float diff = ((const BoxChildShrink *)a)->shrink_amount - ((const BoxChildShrink *)b)->shrink_amount;
+  return diff < 0 ? 1 : (diff == 0 ? 0 : -1);
+}
+
+/* Sort in ascending order by child index */
+static int
+compare_by_child_index (const void *a,
+                        const void *b)
+{
+  return ((const BoxChildShrink *)a)->child_index - ((const BoxChildShrink *)b)->child_index;
+}
+
+static BoxChildShrink *
+compute_shrinks (StBoxLayout *self,
+                 gfloat       for_length,
+                 gfloat       total_shrink)
+{
+  StBoxLayoutPrivate *priv = self->priv;
+  int n_children = g_list_length (priv->children);
+  BoxChildShrink *shrinks = g_new0 (BoxChildShrink, n_children);
+  gfloat shrink_so_far, base_shrink;
+  int n_shrink_children;
+  GList *l;
+  int i;
+
+  /* The effect that we want is that all the children get an equal chance
+   * to expand from their minimum size up to the natural size. Or to put
+   * it a different way, we want to start by shrinking only the child that
+   * can shrink most, then shrink that and the next most shrinkable child,
+   * to the point where we are shrinking everything.
+   */
+
+  /* Find the amount of possible shrink for each child */
+  int n_visible_children = 0;
+  for (l = priv->children, i = 0; l; l = l->next, i++)
+    {
+      gfloat child_min, child_nat;
+
+      shrinks[i].child_index = i;
+      if (CLUTTER_ACTOR_IS_VISIBLE (l->data))
+        {
+          if (priv->is_vertical)
+            clutter_actor_get_preferred_height ((ClutterActor*) l->data,
+                                                for_length,
+                                                &child_min, &child_nat);
+          else
+            clutter_actor_get_preferred_width ((ClutterActor*) l->data,
+                                               for_length,
+                                               &child_min, &child_nat);
+
+          shrinks[i].shrink_amount = MAX (0., child_nat - child_min);
+          n_visible_children++;
+        }
+      else
+        {
+          shrinks[i].shrink_amount = -1.;
+        }
+    }
+
+  /* We want to process children starting from the child with the maximum available
+   * shrink, so sort in this order; !visible children end up at the end */
+  qsort (shrinks, n_children, sizeof (BoxChildShrink), compare_by_shrink_amount);
+
+  /*   +--+
+   *   |  |
+   *   |  | +--
+   *   |  | | |
+   *   |  | | | +-+
+   * --+--+-+-+-+-+----------
+   *   |  | | | | | +-+ +-+
+   *   |  | | | | | | | | |
+   * --+--+-+-+-+-+-+-+------
+   *
+   * We are trying to find the correct position for the upper line the "water mark"
+   * so that total of the portion of the bars above the line is equal to the total
+   * amount we want to shrink.
+   */
+
+  /* Start by moving the line downward, top-of-bar by top-of-bar */
+  shrink_so_far = 0;
+  for (n_shrink_children = 1; n_shrink_children <= n_visible_children; n_shrink_children++)
+    {
+      if (n_shrink_children < n_visible_children)
+        base_shrink = shrinks[n_shrink_children].shrink_amount;
+      else
+        base_shrink = 0;
+      shrink_so_far += n_shrink_children * (shrinks[n_shrink_children - 1].shrink_amount - base_shrink);
+
+      if (shrink_so_far >= total_shrink || n_shrink_children == n_visible_children)
+        break;
+    }
+
+  /* OK, we found enough shrinkage, move it back upwards to the right position */
+  base_shrink += (shrink_so_far - total_shrink) / n_shrink_children;
+  if (base_shrink < 0) /* can't shrink that much, probably round-off error */
+    base_shrink = 0;
+
+  /* Assign the portion above the base shrink line to the shrink_amount */
+  for (i = 0; i < n_shrink_children; i++)
+    shrinks[i].shrink_amount -= base_shrink;
+  for (; i < n_children; i++)
+    shrinks[i].shrink_amount = 0;
+
+  /* And sort back to their original order */
+  qsort (shrinks, n_children, sizeof (BoxChildShrink), compare_by_child_index);
+
+  return shrinks;
+}
+
 static void
 st_box_layout_allocate (ClutterActor          *actor,
                         const ClutterActorBox *box,
@@ -579,10 +700,12 @@ st_box_layout_allocate (ClutterActor          *actor,
   StBoxLayoutPrivate *priv = ST_BOX_LAYOUT (actor)->priv;
   StThemeNode *theme_node = st_widget_get_theme_node (ST_WIDGET (actor));
   ClutterActorBox content_box;
-  gfloat avail_width, avail_height, pref_width, pref_height;
+  gfloat avail_width, avail_height, min_width, natural_width, min_height, natural_height;
-  gfloat position = 0;
+  gfloat position, next_position;
   GList *l;
-  gint n_expand_children, extra_space;
+  gint n_expand_children = 0, i;
+  gfloat expand_amount, shrink_amount;
+  BoxChildShrink *shrinks = NULL;
 
   CLUTTER_ACTOR_CLASS (st_box_layout_parent_class)->allocate (actor, box,
                                                               flags);
@@ -596,9 +719,9 @@ st_box_layout_allocate (ClutterActor          *actor,
   avail_height = content_box.y2 - content_box.y1;
 
   get_content_preferred_height (ST_BOX_LAYOUT (actor), avail_width,
-                                NULL, &pref_height);
+                                &min_height, &natural_height);
   get_content_preferred_width (ST_BOX_LAYOUT (actor), avail_height,
-                               NULL, &pref_width);
+                               &min_width, &natural_width);
 
   /* update adjustments for scrolling */
   if (priv->vadjustment)
@@ -607,7 +730,7 @@ st_box_layout_allocate (ClutterActor          *actor,
 
       g_object_set (G_OBJECT (priv->vadjustment),
                     "lower", 0.0,
-                    "upper", pref_height,
+                    "upper", natural_height,
                     "page-size", avail_height,
                     "step-increment", avail_height / 6,
                     "page-increment", avail_height,
@@ -623,7 +746,7 @@ st_box_layout_allocate (ClutterActor          *actor,
 
       g_object_set (G_OBJECT (priv->hadjustment),
                     "lower", 0.0,
-                    "upper", pref_width,
+                    "upper", natural_width,
                     "page-size", avail_width,
                     "step-increment", avail_width / 6,
                     "page-increment", avail_width,
@@ -633,62 +756,72 @@ st_box_layout_allocate (ClutterActor          *actor,
       st_adjustment_set_value (priv->hadjustment, prev_value);
     }
 
-  /* count the number of children with expand set to TRUE */
+  if (priv->is_vertical)
-  n_expand_children = 0;
-  for (l = priv->children; l; l = l->next)
     {
-      gboolean expand;
+      expand_amount = MAX (0, avail_height - natural_height);
-
+      shrink_amount = MAX (0, natural_height - MAX (avail_height, min_height));
-      if (!CLUTTER_ACTOR_IS_VISIBLE (l->data))
-        continue;
-
-      clutter_container_child_get ((ClutterContainer *) actor,
-                                   (ClutterActor*) l->data,
-                                   "expand", &expand,
-                                   NULL);
-      if (expand)
-        n_expand_children++;
-    }
-
-  if (n_expand_children == 0)
-    {
-      extra_space = 0;
-      n_expand_children = 1;
     }
   else
     {
-      if (priv->is_vertical)
+      expand_amount = MAX (0, avail_width - natural_width);
-        extra_space = (avail_height - pref_height) / n_expand_children;
+      shrink_amount = MAX (0, natural_width - MAX (avail_width, min_width));
-      else
-        extra_space = (avail_width - pref_width) / n_expand_children;
-
-      /* don't shrink anything */
-      if (extra_space < 0)
-        extra_space = 0;
     }
 
+  if (expand_amount > 0)
+    {
+      /* count the number of children with expand set to TRUE */
+      n_expand_children = 0;
+      for (l = priv->children; l; l = l->next)
+        {
+          gboolean expand;
+
+          if (!CLUTTER_ACTOR_IS_VISIBLE (l->data))
+            continue;
+
+          clutter_container_child_get ((ClutterContainer *) actor,
+                                       (ClutterActor*) l->data,
+                                       "expand", &expand,
+                                       NULL);
+          if (expand)
+            n_expand_children++;
+        }
+
+      if (n_expand_children == 0)
+        expand_amount = 0;
+    }
+  else if (shrink_amount > 0)
+    {
+      shrinks = compute_shrinks (ST_BOX_LAYOUT (actor),
+                                 priv->is_vertical ? avail_width : avail_height,
+                                 shrink_amount);
+     }
+
   if (priv->is_vertical)
     position = content_box.y1;
   else
     position = content_box.x1;
 
   if (priv->is_pack_start)
-    l = g_list_last (priv->children);
+    {
+      l = g_list_last (priv->children);
+      i = g_list_length (priv->children);
+    }
   else
-    l = priv->children;
+    {
+      l = priv->children;
+      i = 0;
+    }
 
-  for (l = (priv->is_pack_start) ? g_list_last (priv->children) : priv->children;
+  while (l)
-       l;
-       l = (priv->is_pack_start) ? l->prev : l->next)
     {
       ClutterActor *child = (ClutterActor*) l->data;
       ClutterActorBox child_box;
-      gfloat child_nat;
+      gfloat child_min, child_nat, child_allocated;
       gboolean xfill, yfill, expand;
       StAlign xalign, yalign;
 
       if (!CLUTTER_ACTOR_IS_VISIBLE (child))
-        continue;
+        goto next_child;
 
       clutter_container_child_get ((ClutterContainer*) actor, child,
                                    "x-fill", &xfill,
@@ -701,48 +834,61 @@ st_box_layout_allocate (ClutterActor          *actor,
       if (priv->is_vertical)
         {
           clutter_actor_get_preferred_height (child, avail_width,
-                                              NULL, &child_nat);
+                                              &child_min, &child_nat);
+        }
+      else
+        {
+          clutter_actor_get_preferred_width (child, avail_height,
+                                             &child_min, &child_nat);
+        }
 
-          child_box.y1 = position;
+      child_allocated = child_nat;
-          if (expand)
+      if (expand_amount > 0 && expand)
-            child_box.y2 = position + child_nat + extra_space;
+        child_allocated +=  expand_amount / n_expand_children;
-          else
+      else if (shrink_amount > 0)
-            child_box.y2 = position + child_nat;
+        child_allocated -= shrinks[i].shrink_amount;
+
+      next_position = position + child_allocated;
+
+      if (priv->is_vertical)
+        {
+          child_box.y1 = (int)(0.5 + position);
+          child_box.y2 = (int)(0.5 + next_position);
           child_box.x1 = content_box.x1;
           child_box.x2 = content_box.x2;
 
           _st_allocate_fill (child, &child_box, xalign, yalign, xfill, yfill);
           clutter_actor_allocate (child, &child_box, flags);
 
-          if (expand)
-            position += (child_nat + priv->spacing + extra_space);
-          else
-            position += (child_nat + priv->spacing);
         }
       else
         {
-
+          child_box.x1 = (int)(0.5 + position);
-          clutter_actor_get_preferred_width (child, avail_height,
+          child_box.x2 = (int)(0.5 + next_position);
-                                             NULL, &child_nat);
-
-          child_box.x1 = position;
-
-          if (expand)
-            child_box.x2 = position + child_nat + extra_space;
-          else
-            child_box.x2 = position + child_nat;
-
           child_box.y1 = content_box.y1;
           child_box.y2 = content_box.y2;
+
           _st_allocate_fill (child, &child_box, xalign, yalign, xfill, yfill);
           clutter_actor_allocate (child, &child_box, flags);
+        }
 
-          if (expand)
+      position = next_position + priv->spacing;
-            position += (child_nat + priv->spacing + extra_space);
+
-          else
+    next_child:
-            position += (child_nat + priv->spacing);
+      if (priv->is_pack_start)
+        {
+          l = l->prev;
+          i--;
+        }
+      else
+        {
+          l = l->next;
+          i++;
         }
     }
+
+  if (shrinks)
+    g_free (shrinks);
 }
 
 static void

tests/interactive/box-layout.js

@@ -8,32 +8,79 @@ const UI = imports.testcommon.ui;
 UI.init();
 let stage = Clutter.Stage.get_default();
 
-let b = new St.BoxLayout({ vertical: true,
+let vbox = new St.BoxLayout({ vertical: true,
-			     width: stage.width,
+                              width: stage.width,
-			     height: stage.height });
+                              height: stage.height,
-stage.add_actor(b);
+                              spacing: 10,
+                              style: 'padding: 10px' });
+stage.add_actor(vbox);
 
-let b2 = new St.BoxLayout();
+////////////////////////////////////////////////////////////////////////////////
-b.add(b2, { expand: true, fill: true });
 
-let r1 = new St.BoxLayout({ style_class: 'red',
+let colored_boxes = new St.BoxLayout({ vertical: true,
-                              width: 10,
+                                       width:  200,
-                              height: 10 });
+                                       height: 200,
-b2.add(r1, { expand: true });
+                                       style: 'border: 2px solid black;' });
+vbox.add(colored_boxes, { x_fill: false,
+                          x_align: St.Align.MIDDLE });
 
-let r2 = new St.BoxLayout({ style_class: 'green',
+let b2 = new St.BoxLayout({ style: 'border: 2px solid #666666' });
-                              width: 10,
+colored_boxes.add(b2, { expand: true });
-                              height: 10 });
-b2.add(r2, { expand: true,
-             x_fill: false,
-             x_align: St.Align.MIDDLE,
-             y_fill: false,
-             y_align: St.Align.MIDDLE });
 
-let r3 = new St.BoxLayout({ style_class: 'blue',
+b2.add(new St.Label({ text: "Expand",
-                              width: 10,
+                      style: 'border: 1px solid #aaaaaa; '
-                              height: 10 });
+                             + 'background: #ffeecc' }),
-b.add(r3);
+       { expand: true });
+b2.add(new St.Label({ text: "Expand\nNo Fill",
+                      style: 'border: 1px solid #aaaaaa; '
+                             + 'background: #ccffaa' }),
+       { expand: true,
+         x_fill: false,
+         x_align: St.Align.MIDDLE,
+         y_fill: false,
+         y_align: St.Align.MIDDLE });
+
+colored_boxes.add(new St.Label({ text: "Default",
+                                 style: 'border: 1px solid #aaaaaa; '
+                                        + 'background: #cceeff' }));
+
+////////////////////////////////////////////////////////////////////////////////
+
+function createCollapsableBox(width) {
+    let b = new St.BoxLayout({ width: width,
+                               style: 'border: 1px solid black;'
+                                      + 'font: 13px Sans;' });
+    b.add(new St.Label({ text: "Very Very Very Long",
+                         style: 'background: #ffaacc;'
+                                + 'padding: 5px; '
+                                + 'border: 1px solid #666666;' }),
+          { expand: true });
+    b.add(new St.Label({ text: "Very Very Long",
+                         style: 'background: #ffeecc; '
+                                + 'padding: 5px; '
+                                + 'border: 1px solid #666666;' }),
+          { expand: true });
+    b.add(new St.Label({ text: "Very Long",
+                         style: 'background: #ccffaa; '
+                                + 'padding: 5px; '
+                                + 'border: 1px solid #666666;' }),
+          { expand: true });
+    b.add(new St.Label({ text: "Short",
+                         style: 'background: #cceeff; '
+                                + 'padding: 5px; '
+                                + 'border: 1px solid #666666;' }),
+          { expand: true });
+
+    return b;
+}
+
+for (let width = 200; width <= 500; width += 60 ) {
+    vbox.add(createCollapsableBox (width),
+             { x_fill: false,
+               x_align: St.Align.MIDDLE });
+}
+
+////////////////////////////////////////////////////////////////////////////////
 
 stage.show();
 Clutter.main();