stack: More readability when adding transitions

This small refactor makes the code more readable when adding more
transition types that have left, right, up, and down variations.

It adds inline boolean functions to tell information about transition
types (avoiding long if clauses) and changes long chains of "else if
(transition_type == ...)" into switch statements. Both are only likely
to get longer as more transition types are added.

https://bugzilla.gnome.org/show_bug.cgi?id=726676

1 files changed, 94 insertions, 46 deletions

diff --git a/gtk/gtkstack.c b/gtk/gtkstack.c
index 042f8fd95b..b248161632 100644
--- a/gtk/gtkstack.c
+++ b/gtk/gtkstack.c
@@ -675,6 +675,77 @@ ease_out_cubic (double t)
   return p * p * p + 1;
 }
 
+static inline gboolean
+is_left_transition (GtkStackTransitionType transition_type)
+{
+  return (transition_type == GTK_STACK_TRANSITION_TYPE_SLIDE_LEFT ||
+          transition_type == GTK_STACK_TRANSITION_TYPE_OVER_LEFT);
+}
+
+static inline gboolean
+is_right_transition (GtkStackTransitionType transition_type)
+{
+  return (transition_type == GTK_STACK_TRANSITION_TYPE_SLIDE_RIGHT ||
+          transition_type == GTK_STACK_TRANSITION_TYPE_OVER_RIGHT);
+}
+
+static inline gboolean
+is_up_transition (GtkStackTransitionType transition_type)
+{
+  return (transition_type == GTK_STACK_TRANSITION_TYPE_SLIDE_UP ||
+          transition_type == GTK_STACK_TRANSITION_TYPE_OVER_UP);
+}
+
+static inline gboolean
+is_down_transition (GtkStackTransitionType transition_type)
+{
+  return (transition_type == GTK_STACK_TRANSITION_TYPE_SLIDE_DOWN ||
+          transition_type == GTK_STACK_TRANSITION_TYPE_OVER_DOWN);
+}
+
+/* Transitions that cause the bin window to move */
+static inline gboolean
+is_window_moving_transition (GtkStackTransitionType transition_type)
+{
+  return (transition_type == GTK_STACK_TRANSITION_TYPE_SLIDE_LEFT ||
+          transition_type == GTK_STACK_TRANSITION_TYPE_SLIDE_RIGHT ||
+          transition_type == GTK_STACK_TRANSITION_TYPE_SLIDE_UP ||
+          transition_type == GTK_STACK_TRANSITION_TYPE_SLIDE_DOWN ||
+          transition_type == GTK_STACK_TRANSITION_TYPE_OVER_UP ||
+          transition_type == GTK_STACK_TRANSITION_TYPE_OVER_DOWN ||
+          transition_type == GTK_STACK_TRANSITION_TYPE_OVER_LEFT ||
+          transition_type == GTK_STACK_TRANSITION_TYPE_OVER_RIGHT);
+}
+
+/* Transitions that change direction depending on the relative order of the
+old and new child */
+static inline gboolean
+is_direction_dependent_transition (GtkStackTransitionType transition_type)
+{
+  return (transition_type == GTK_STACK_TRANSITION_TYPE_SLIDE_LEFT_RIGHT ||
+          transition_type == GTK_STACK_TRANSITION_TYPE_SLIDE_UP_DOWN ||
+          transition_type == GTK_STACK_TRANSITION_TYPE_OVER_UP_DOWN);
+}
+
+/* Returns simple transition type for a direction dependent transition, given
+whether the new child (the one being switched to) is first in the stacking order
+(added earlier). */
+static inline GtkStackTransitionType
+get_simple_transition_type (gboolean               new_child_first,
+                            GtkStackTransitionType transition_type)
+{
+  switch (transition_type)
+    {
+    case GTK_STACK_TRANSITION_TYPE_SLIDE_LEFT_RIGHT:
+      return new_child_first ? GTK_STACK_TRANSITION_TYPE_SLIDE_RIGHT : GTK_STACK_TRANSITION_TYPE_SLIDE_LEFT;
+    case GTK_STACK_TRANSITION_TYPE_SLIDE_UP_DOWN:
+      return new_child_first ? GTK_STACK_TRANSITION_TYPE_SLIDE_DOWN : GTK_STACK_TRANSITION_TYPE_SLIDE_UP;
+    case GTK_STACK_TRANSITION_TYPE_OVER_UP_DOWN:
+      return new_child_first ? GTK_STACK_TRANSITION_TYPE_UNDER_DOWN : GTK_STACK_TRANSITION_TYPE_OVER_UP;
+    }
+  return transition_type;
+}
+
 static gint
 get_bin_window_x (GtkStack      *stack,
                   GtkAllocation *allocation)
@@ -684,11 +755,9 @@ get_bin_window_x (GtkStack      *stack,
 
   if (priv->transition_pos < 1.0)
     {
-      if (priv->active_transition_type == GTK_STACK_TRANSITION_TYPE_SLIDE_LEFT ||
-          priv->active_transition_type == GTK_STACK_TRANSITION_TYPE_OVER_LEFT)
+      if (is_left_transition (priv->active_transition_type))
         x = allocation->width * (1 - ease_out_cubic (priv->transition_pos));
-      if (priv->active_transition_type == GTK_STACK_TRANSITION_TYPE_SLIDE_RIGHT ||
-          priv->active_transition_type == GTK_STACK_TRANSITION_TYPE_OVER_RIGHT)
+      if (is_right_transition (priv->active_transition_type))
         x = -allocation->width * (1 - ease_out_cubic (priv->transition_pos));
     }
 
@@ -704,11 +773,9 @@ get_bin_window_y (GtkStack      *stack,
 
   if (priv->transition_pos < 1.0)
     {
-      if (priv->active_transition_type == GTK_STACK_TRANSITION_TYPE_SLIDE_UP ||
-          priv->active_transition_type == GTK_STACK_TRANSITION_TYPE_OVER_UP)
+      if (is_up_transition (priv->active_transition_type))
         y = allocation->height * (1 - ease_out_cubic (priv->transition_pos));
-      if (priv->active_transition_type == GTK_STACK_TRANSITION_TYPE_SLIDE_DOWN ||
-          priv->active_transition_type == GTK_STACK_TRANSITION_TYPE_OVER_DOWN)
+      if (is_down_transition(priv->active_transition_type))
         y = -allocation->height * (1 - ease_out_cubic (priv->transition_pos));
     }
 
@@ -726,14 +793,7 @@ gtk_stack_set_transition_position (GtkStack *stack,
   gtk_widget_queue_draw (GTK_WIDGET (stack));
 
   if (priv->bin_window != NULL &&
-      (priv->active_transition_type == GTK_STACK_TRANSITION_TYPE_SLIDE_LEFT ||
-       priv->active_transition_type == GTK_STACK_TRANSITION_TYPE_SLIDE_RIGHT ||
-       priv->active_transition_type == GTK_STACK_TRANSITION_TYPE_SLIDE_UP ||
-       priv->active_transition_type == GTK_STACK_TRANSITION_TYPE_SLIDE_DOWN ||
-       priv->active_transition_type == GTK_STACK_TRANSITION_TYPE_OVER_UP ||
-       priv->active_transition_type == GTK_STACK_TRANSITION_TYPE_OVER_DOWN ||
-       priv->active_transition_type == GTK_STACK_TRANSITION_TYPE_OVER_LEFT ||
-       priv->active_transition_type == GTK_STACK_TRANSITION_TYPE_OVER_RIGHT))
+      is_window_moving_transition (priv->active_transition_type))
     {
       GtkAllocation allocation;
       gtk_widget_get_allocation (GTK_WIDGET (stack), &allocation);
@@ -830,18 +890,21 @@ effective_transition_type (GtkStack               *stack,
 {
   if (gtk_widget_get_direction (GTK_WIDGET (stack)) == GTK_TEXT_DIR_RTL)
     {
-      if (transition_type == GTK_STACK_TRANSITION_TYPE_SLIDE_LEFT)
-        return GTK_STACK_TRANSITION_TYPE_SLIDE_RIGHT;
-      else if (transition_type == GTK_STACK_TRANSITION_TYPE_SLIDE_RIGHT)
-        return GTK_STACK_TRANSITION_TYPE_SLIDE_LEFT;
-      else if (transition_type == GTK_STACK_TRANSITION_TYPE_OVER_LEFT)
-        return GTK_STACK_TRANSITION_TYPE_OVER_RIGHT;
-      else if (transition_type == GTK_STACK_TRANSITION_TYPE_OVER_RIGHT)
-        return GTK_STACK_TRANSITION_TYPE_OVER_LEFT;
-      else if (transition_type == GTK_STACK_TRANSITION_TYPE_UNDER_LEFT)
-        return GTK_STACK_TRANSITION_TYPE_UNDER_RIGHT;
-      else if (transition_type == GTK_STACK_TRANSITION_TYPE_UNDER_RIGHT)
-        return GTK_STACK_TRANSITION_TYPE_UNDER_LEFT;
+      switch (transition_type)
+        {
+        case GTK_STACK_TRANSITION_TYPE_SLIDE_LEFT:
+          return GTK_STACK_TRANSITION_TYPE_SLIDE_RIGHT;
+        case GTK_STACK_TRANSITION_TYPE_SLIDE_RIGHT:
+          return GTK_STACK_TRANSITION_TYPE_SLIDE_LEFT;
+        case GTK_STACK_TRANSITION_TYPE_OVER_LEFT:
+          return GTK_STACK_TRANSITION_TYPE_OVER_RIGHT;
+        case GTK_STACK_TRANSITION_TYPE_OVER_RIGHT:
+          return GTK_STACK_TRANSITION_TYPE_OVER_LEFT;
+        case GTK_STACK_TRANSITION_TYPE_UNDER_LEFT:
+          return GTK_STACK_TRANSITION_TYPE_UNDER_RIGHT;
+        case GTK_STACK_TRANSITION_TYPE_UNDER_RIGHT:
+          return GTK_STACK_TRANSITION_TYPE_UNDER_LEFT;
+        }
     }
 
   return transition_type;
@@ -930,15 +993,11 @@ set_visible_child (GtkStack               *stack,
     gtk_widget_set_child_visible (child_info->widget, TRUE);
 
   if ((child_info == NULL || priv->last_visible_child == NULL) &&
-      (transition_type == GTK_STACK_TRANSITION_TYPE_SLIDE_LEFT_RIGHT ||
-       transition_type == GTK_STACK_TRANSITION_TYPE_SLIDE_UP_DOWN ||
-       transition_type == GTK_STACK_TRANSITION_TYPE_OVER_UP_DOWN))
+      is_direction_dependent_transition (transition_type))
     {
       transition_type = GTK_STACK_TRANSITION_TYPE_NONE;
     }
-  else if (transition_type == GTK_STACK_TRANSITION_TYPE_SLIDE_LEFT_RIGHT ||
-	   transition_type == GTK_STACK_TRANSITION_TYPE_SLIDE_UP_DOWN ||
-	   transition_type == GTK_STACK_TRANSITION_TYPE_OVER_UP_DOWN)
+  else if (is_direction_dependent_transition (transition_type))
     {
       gboolean i_first = FALSE;
       for (l = priv->children; l != NULL; l = g_list_next (l))
@@ -952,18 +1011,7 @@ set_visible_child (GtkStack               *stack,
 	    break;
         }
 
-      if (transition_type == GTK_STACK_TRANSITION_TYPE_SLIDE_LEFT_RIGHT)
-	{
-	  transition_type = i_first ? GTK_STACK_TRANSITION_TYPE_SLIDE_RIGHT : GTK_STACK_TRANSITION_TYPE_SLIDE_LEFT;
-	}
-      else if (transition_type == GTK_STACK_TRANSITION_TYPE_SLIDE_UP_DOWN)
-	{
-	  transition_type = i_first ? GTK_STACK_TRANSITION_TYPE_SLIDE_DOWN : GTK_STACK_TRANSITION_TYPE_SLIDE_UP;
-	}
-      else if (transition_type == GTK_STACK_TRANSITION_TYPE_OVER_UP_DOWN)
-	{
-	  transition_type = i_first ? GTK_STACK_TRANSITION_TYPE_UNDER_DOWN : GTK_STACK_TRANSITION_TYPE_OVER_UP;
-	}
+      transition_type = get_simple_transition_type (i_first, transition_type);
     }
 
   gtk_widget_queue_resize (GTK_WIDGET (stack));