From 0015ebc4a8f269f6888fcacef3e83e3167241d67 Mon Sep 17 00:00:00 2001
From: Ray Strode <rstrode@redhat.com>
Date: Fri, 24 Jun 2016 07:53:49 -0400
Subject: [PATCH] headerbar: support expand property for children

The header bar currently ignores the expand property on its
children. This commit changes the code to honor that property.

It divvies up any free space and distributes it equally to packed
children (with any left over space given out a pixel at a time
on a first come, first serve basis).

This commit also adds support for the title widget to be made
expandable.

It accomplishes this by using up the padding the title widget
is centered with.

https://bugzilla.gnome.org/show_bug.cgi?id=724332
---
 docs/reference/gtk/migrating-3xtoy.xml |  7 +++
 gtk/gtkheaderbar.c                     | 59 ++++++++++++++++++++++++++
 2 files changed, 66 insertions(+)

diff --git a/docs/reference/gtk/migrating-3xtoy.xml b/docs/reference/gtk/migrating-3xtoy.xml
index b546cbaa70..f140a4a876 100644
--- a/docs/reference/gtk/migrating-3xtoy.xml
+++ b/docs/reference/gtk/migrating-3xtoy.xml
@@ -426,5 +426,12 @@
       and #GtkScrolledWindow:max-content-height will allow control over the
       size of the scrolled window.
     </para>
+
+    <para>
+      GtkHeaderBar now respects the hexpand property for its custom title
+      widget and its packed children. This change may inadvertently cause the
+      layout of those children to change, if they unintentionally had hexpand
+      set before.
+    </para>
   </section>
 </chapter>
diff --git a/gtk/gtkheaderbar.c b/gtk/gtkheaderbar.c
index 031199b2a7..47fb70c22d 100644
--- a/gtk/gtkheaderbar.c
+++ b/gtk/gtkheaderbar.c
@@ -997,7 +997,11 @@ gtk_header_bar_allocate_contents (GtkCssGadget        *gadget,
   gint nvis_children;
   gint title_minimum_size;
   gint title_natural_size;
+  gboolean title_expands;
   gint start_width, end_width;
+  gint uniform_expand_bonus[2] = { 0 };
+  gint leftover_expand_bonus[2] = { 0 };
+  gint nexpand_children[2] = { 0 };
   gint side[2];
   GList *l;
   gint i;
@@ -1024,6 +1028,9 @@ gtk_header_bar_allocate_contents (GtkCssGadget        *gadget,
       if (!gtk_widget_get_visible (child->widget))
         continue;
 
+      if (gtk_widget_compute_expand (child->widget, GTK_ORIENTATION_HORIZONTAL))
+        nexpand_children[child->pack_type]++;
+
       gtk_widget_get_preferred_width_for_height (child->widget,
                                                  height,
                                                  &sizes[i].minimum_size,
@@ -1050,6 +1057,8 @@ gtk_header_bar_allocate_contents (GtkCssGadget        *gadget,
                                                &title_natural_size);
   width -= title_natural_size;
 
+  title_expands = gtk_widget_compute_expand (title_widget, GTK_ORIENTATION_HORIZONTAL);
+
   start_width = 0;
   if (priv->titlebar_start_box != NULL)
     {
@@ -1095,6 +1104,31 @@ gtk_header_bar_allocate_contents (GtkCssGadget        *gadget,
         }
     }
 
+  /* figure out how much space is left on each side of the title,
+   * and earkmark that space for the expanded children.
+   *
+   * If the title itself is expanded, then it gets half the spoils
+   * from each side.
+   */
+  for (packing = GTK_PACK_START; packing <= GTK_PACK_END; packing++)
+    {
+      gint side_free_space;
+
+      side_free_space = allocation->width / 2 - title_natural_size / 2 - side[packing];
+
+      if (side_free_space > 0 && nexpand_children[packing] > 0)
+        {
+          width -= side_free_space;
+
+          if (title_expands)
+            side_free_space -= side_free_space / 2;
+
+          side[packing] += side_free_space;
+          uniform_expand_bonus[packing] = side_free_space / nexpand_children[packing];
+          leftover_expand_bonus[packing] = side_free_space % nexpand_children[packing];
+        }
+    }
+
   /* allocate the children on both sides of the title */
   for (packing = GTK_PACK_START; packing <= GTK_PACK_END; packing++)
     {
@@ -1117,6 +1151,22 @@ gtk_header_bar_allocate_contents (GtkCssGadget        *gadget,
 
           child_size = sizes[i].minimum_size;
 
+          /* if this child is expanded, give it extra space from the reserves */
+          if (gtk_widget_compute_expand (child->widget, GTK_ORIENTATION_HORIZONTAL))
+            {
+              gint expand_bonus;
+
+              expand_bonus = uniform_expand_bonus[packing];
+
+              if (leftover_expand_bonus[packing] > 0)
+                {
+                  expand_bonus++;
+                  leftover_expand_bonus[packing]--;
+                }
+
+              child_size += expand_bonus;
+            }
+
           child_allocation.width = child_size;
 
           if (packing == GTK_PACK_START)
@@ -1153,6 +1203,15 @@ gtk_header_bar_allocate_contents (GtkCssGadget        *gadget,
   child_allocation.x = allocation->x + (allocation->width - child_size) / 2;
   child_allocation.width = child_size;
 
+  /* if the title widget is expanded, then grow it by all the available
+   * free space, and recenter it
+   */
+  if (title_expands && width > 0)
+    {
+      child_allocation.width += width;
+      child_allocation.x -= width / 2;
+    }
+
   if (allocation->x + side[0] > child_allocation.x)
     child_allocation.x = allocation->x + side[0];
   else if (allocation->x + allocation->width - side[1] < child_allocation.x + child_allocation.width)