center box: complete the baseline support

When there is no externally allocated baseline, we should
do the same thing that GtkBox does, and determine one from
the children that want baseline alignment.

This commit adds a GtkCenterBox::baseline-position property
with setters and getters.

docs/reference/gtk/gtk4-sections.txt

@@ -352,6 +352,8 @@ gtk_center_box_set_end_widget
 gtk_center_box_get_start_widget
 gtk_center_box_get_center_widget
 gtk_center_box_get_end_widget
+gtk_center_box_set_baseline_position
+gtk_center_box_get_baseline_position
 <PRIVATE>
 GTK_TYPE_CENTER_BOX
 GTK_CENTER_BOX

gtk/gtkcenterbox.c

@@ -59,6 +59,9 @@
 #include "gtkorientableprivate.h"
 #include "gtkbuildable.h"
 #include "gtksizerequest.h"
+#include "gtktypebuiltins.h"
+#include "gtkprivate.h"
+#include "gtkintl.h"
 
 struct _GtkCenterBox
 {
@@ -69,6 +72,7 @@ struct _GtkCenterBox
   GtkWidget *end_widget;
 
   GtkOrientation orientation;
+  GtkBaselinePosition baseline_pos;
 };
 
 struct _GtkCenterBoxClass
@@ -79,6 +83,7 @@ struct _GtkCenterBoxClass
 
 enum {
   PROP_0,
+  PROP_BASELINE_POSITION,
   PROP_ORIENTATION
 };
 
@@ -386,6 +391,8 @@ gtk_center_box_size_allocate (GtkWidget     *widget,
       baseline = -1;
     }
 
+  /* Allocate child sizes */
+
   gtk_center_box_distribute (self, for_size, size, sizes);
 
   if (self->orientation == GTK_ORIENTATION_HORIZONTAL &&
@@ -408,6 +415,65 @@ gtk_center_box_size_allocate (GtkWidget     *widget,
       child_size[2] = sizes[2].minimum_size;
     }
 
+  /* Determine baseline */
+  if (self->orientation == GTK_ORIENTATION_HORIZONTAL &&
+      baseline == -1)
+    {
+      int min_above, nat_above;
+      int min_below, nat_below;
+      gboolean have_baseline;
+
+      have_baseline = FALSE;
+      min_above = nat_above = 0;
+      min_below = nat_below = 0;
+
+      for (i = 0; i < 3; i++)
+        {
+          if (gtk_widget_get_valign (child[i]) == GTK_ALIGN_BASELINE)
+            {
+              int child_min_height, child_nat_height;
+              int child_min_baseline, child_nat_baseline;
+
+              child_min_baseline = child_nat_baseline = -1;
+
+              gtk_widget_measure (child[i], GTK_ORIENTATION_VERTICAL,
+                                  child_size[i],
+                                  &child_min_height, &child_nat_height,
+                                  &child_min_baseline, &child_nat_baseline);
+
+              if (child_min_baseline >= 0)
+                {
+                  have_baseline = TRUE;
+                  min_below = MAX (min_below, child_min_height - child_min_baseline);
+                  nat_below = MAX (nat_below, child_nat_height - child_nat_baseline);
+                  min_above = MAX (min_above, child_min_baseline);
+                  nat_above = MAX (nat_above, child_nat_baseline);
+                }
+            }
+        }
+
+      if (have_baseline)
+        {
+          /* TODO: This is purely based on the minimum baseline.
+           * When things fit we should use the natural one
+           */
+          switch (self->baseline_pos)
+            {
+            case GTK_BASELINE_POSITION_TOP:
+              baseline = min_above;
+              break;
+            case GTK_BASELINE_POSITION_CENTER:
+              baseline = min_above + (allocation->height - (min_above + min_below)) / 2;
+              break;
+            case GTK_BASELINE_POSITION_BOTTOM:
+              baseline = allocation->height - min_below;
+              break;
+            }
+        }
+    }
+
+  /* Allocate child positions */
+
   child_pos[0] = 0;
   child_pos[1] = (size / 2) - (child_size[1] / 2);
   child_pos[2] = size - child_size[2];
@@ -443,7 +509,7 @@ gtk_center_box_size_allocate (GtkWidget     *widget,
           child_allocation.height = child_size[i];
         }
 
-      gtk_widget_size_allocate_with_baseline (child[i], &child_allocation, baseline);
+      gtk_widget_size_allocate_with_baseline (child[i], &child_allocation, allocation->y + baseline);
       gtk_widget_get_clip (child[i], &child_clip);
       gdk_rectangle_union (&clip, &clip, &child_clip);
     }
@@ -534,6 +600,10 @@ gtk_center_box_set_property (GObject      *object,
 
   switch (prop_id)
     {
+    case PROP_BASELINE_POSITION:
+      gtk_center_box_set_baseline_position (self, g_value_get_enum (value));
+      break;
+
     case PROP_ORIENTATION:
       {
         GtkOrientation orientation = g_value_get_enum (value);
@@ -563,6 +633,10 @@ gtk_center_box_get_property (GObject    *object,
 
   switch (prop_id)
     {
+    case PROP_BASELINE_POSITION:
+      g_value_set_enum (value, self->baseline_pos);
+      break;
+
     case PROP_ORIENTATION:
       g_value_set_enum (value, self->orientation);
       break;
@@ -590,6 +664,15 @@ gtk_center_box_class_init (GtkCenterBoxClass *klass)
 
   g_object_class_override_property (object_class, PROP_ORIENTATION, "orientation");
 
+  g_object_class_install_property (object_class, PROP_BASELINE_POSITION,
+          g_param_spec_enum ("baseline-position",
+                             P_("Baseline position"),
+                             P_("The position of the baseline aligned widgets if extra space is available"),
+                             GTK_TYPE_BASELINE_POSITION,
+                             GTK_BASELINE_POSITION_CENTER,
+                             GTK_PARAM_READWRITE|G_PARAM_EXPLICIT_NOTIFY));
+
+
   gtk_widget_class_set_accessible_role (widget_class, ATK_ROLE_FILLER);
   gtk_widget_class_set_css_name (widget_class, "box");
 }
@@ -604,6 +687,7 @@ gtk_center_box_init (GtkCenterBox *self)
   self->end_widget = NULL;
 
   self->orientation = GTK_ORIENTATION_HORIZONTAL;
+  self->baseline_pos = GTK_BASELINE_POSITION_CENTER;
 }
 
 /**
@@ -737,3 +821,51 @@ gtk_center_box_get_end_widget (GtkCenterBox *self)
 {
   return self->end_widget;
 }
+
+/**
+ * gtk_center_box_set_baseline_position:
+ * @self: a #GtkCenterBox
+ * @position: a #GtkBaselinePosition
+ *
+ * Sets the baseline position of a center box.
+ *
+ * This affects only horizontal boxes with at least one baseline
+ * aligned child. If there is more vertical space available than
+ * requested, and the baseline is not allocated by the parent then
+ * @position is used to allocate the baseline wrt. the extra space
+ * available.
+ *
+ * Since: 3.92
+ */
+void
+gtk_center_box_set_baseline_position (GtkCenterBox        *self,
+                                      GtkBaselinePosition  position)
+{
+  g_return_if_fail (GTK_IS_CENTER_BOX (self));
+
+  if (self->baseline_pos != position)
+    {
+      self->baseline_pos = position;
+      g_object_notify (G_OBJECT (self), "baseline-position");
+      gtk_widget_queue_resize (GTK_WIDGET (self));
+    }
+}
+
+/**
+ * gtk_center_box_get_baseline_position:
+ * @self: a #GtkCenterBox
+ *
+ * Gets the value set by gtk_center_box_set_baseline_position().
+ *
+ * Returns: the baseline position
+ *
+ * Since: 3.92
+ */
+GtkBaselinePosition
+gtk_center_box_get_baseline_position (GtkCenterBox *self)
+{
+  g_return_val_if_fail (GTK_IS_CENTER_BOX (self), GTK_BASELINE_POSITION_CENTER);
+
+  return self->baseline_pos;
+}
+

gtk/gtkcenterbox.h

@@ -56,5 +56,10 @@ GtkWidget * gtk_center_box_get_center_widget (GtkCenterBox *self);
 GDK_AVAILABLE_IN_3_92
 GtkWidget * gtk_center_box_get_end_widget    (GtkCenterBox *self);
 
+GDK_AVAILABLE_IN_3_92
+void                gtk_center_box_set_baseline_position (GtkCenterBox        *self,
+                                                          GtkBaselinePosition  position);
+GDK_AVAILABLE_IN_3_92
+GtkBaselinePosition gtk_center_box_get_baseline_position (GtkCenterBox        *self);
 
 #endif