implemented smoothstep alpha function

ChangeLog

@@ -1,3 +1,13 @@
+2007-05-16  Tomas Frydrych  <tf@openedhand.com>
+	
+	* clutter/clutter-alpha.h:
+	* clutter/clutter-alpha.c:
+	* doc/reference/clutter-sections.txt:
+	* doc/rererence/clutter.types:
+	* doc/reference/tmpl/clutter-alpha.sgml:
+	clutter_smoothstep_func alpha function, 
+	ClutterSmoothstep struct for smoothstep function data.
+
 2007-05-16  Matthew Allum  <mallum@openedhand.com>
 
 	* clutter/clutter-backend.c:

clutter/clutter-alpha.c

@@ -6,8 +6,9 @@
  * Authored By Matthew Allum  <mallum@openedhand.com>
  *             Jorn Baayen  <jorn@openedhand.com>
  *             Emmanuele Bassi  <ebassi@openedhand.com>
+ *             Tomas Frydrych <tf@openedhand.com>
  *
- * Copyright (C) 2006 OpenedHand
+ * Copyright (C) 2006, 2007 OpenedHand
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Lesser General Public
@@ -647,3 +648,127 @@ clutter_square_func (ClutterAlpha *alpha,
   return (current_frame_num > (n_frames / 2)) ? CLUTTER_ALPHA_MAX_ALPHA
                                               : 0;
 }
+
+/**
+ * clutter_smoothstep_copy:
+ * @smoothstep: a #ClutterSmoothstep
+ *
+ * Makes an allocated copy of a smoothstep.
+ *
+ * Return value: the copied smoothstep.
+ *
+ * Since: 0.4
+ */
+ClutterSmoothstep *
+clutter_smoothstep_copy (const ClutterSmoothstep *smoothstep)
+{
+  ClutterSmoothstep *copy;
+
+  copy = g_slice_new0 (ClutterSmoothstep);
+  
+  *copy = *smoothstep;
+
+  return copy;
+}
+
+/**
+ * clutter_smoothstep_free:
+ * @smoothstep: a #ClutterSmoothstep
+ *
+ * Frees the memory of an allocated smoothstep.
+ *
+ * Since: 0.4
+ */
+void
+clutter_smoothstep_free (ClutterSmoothstep *smoothstep)
+{
+  if (G_LIKELY (smoothstep))
+    {
+      g_slice_free (ClutterSmoothstep, smoothstep);
+    }
+}
+
+GType
+clutter_smoothstep_get_type (void)
+{
+  static GType our_type = 0;
+
+  if (G_UNLIKELY (!our_type))
+    {
+      our_type =
+        g_boxed_type_register_static ("ClutterSmoothstep",
+                                      (GBoxedCopyFunc) clutter_smoothstep_copy,
+                                      (GBoxedFreeFunc) clutter_smoothstep_free);
+    }
+
+  return our_type;
+}
+
+/**
+ * clutter_smoothstep_func:
+ * @alpha: a #ClutterAlpha
+ * @data: pointer to a #ClutterSmoothstep defining the minimum and
+ * maximum thresholds for the smoothstep as supplied to
+ * clutter_alpha_set_func().
+ *
+ * Convenience alpha function for a smoothstep curve. You can use this
+ * function as the alpha function for clutter_alpha_set_func().
+ *
+ * Return value: an alpha value
+ *
+ * Since: 0.4
+ */
+guint32
+clutter_smoothstep_func (ClutterAlpha  * alpha,
+			 gpointer      * data)
+{
+  ClutterSmoothstep * smoothstep = data;
+  ClutterTimeline   * timeline;
+  gint                frame;
+  gint                n_frames;
+  gint32              r;
+  gint32              x; 
+
+  /*
+   * The smoothstep function uses f(x) = -2x^3 + 3x^2 where x is from <0,1>,
+   * and precission is critical -- we use 8.24 fixed format for this operation.
+   * The earlier operations involve division, which we cannot do in 8.24 for
+   * numbers in <0,1> we use ClutterFixed.
+   */
+  
+  g_return_val_if_fail (data, 0);
+  
+  timeline = clutter_alpha_get_timeline (alpha);
+  frame    = clutter_timeline_get_current_frame (timeline);
+  n_frames = clutter_timeline_get_n_frames (timeline);
+
+  r = CFX_DIV (frame, n_frames);
+
+  if (r <= smoothstep->min)
+      return 0;
+
+  if (r >= smoothstep->max)
+      return CLUTTER_ALPHA_MAX_ALPHA;
+
+  /*
+   * Normalize x for the smoothstep polynomal.
+   *
+   * Convert result to 8.24 for next step.
+   */
+  x = CFX_DIV ((r - smoothstep->min), (smoothstep->max - smoothstep->min))
+      << 8;
+
+  /*
+   * f(x) = -2x^3 + 3x^2
+   * 
+   * Convert result to ClutterFixed to avoid overflow in next step.
+   */
+  r = ((x >> 12) * (x >> 12) * 3 - (x >> 15) * (x >> 16) * (x >> 16)) >> 8;
+
+  g_debug ("Frame %d of %d, x %f, ret %f",
+	   frame, n_frames,
+	   CLUTTER_FIXED_TO_DOUBLE (x >> 8),
+	   CLUTTER_FIXED_TO_DOUBLE (r));
+	   
+  return CFX_INT (r * CLUTTER_ALPHA_MAX_ALPHA);
+}

clutter/clutter-alpha.h

@@ -6,8 +6,9 @@
  * Authored By Matthew Allum  <mallum@openedhand.com>
  *             Jorn Baayen  <jorn@openedhand.com>
  *             Emmanuele Bassi  <ebassi@openedhand.com>
+ *             Tomas Frydrych <tf@openedhand.com>
  *
- * Copyright (C) 2006 OpenedHand
+ * Copyright (C) 2006, 2007 OpenedHand
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Lesser General Public
@@ -30,6 +31,7 @@
 
 #include <glib-object.h>
 #include <clutter/clutter-timeline.h>
+#include <clutter/clutter-fixed.h>
 
 G_BEGIN_DECLS
 
@@ -106,6 +108,21 @@ ClutterTimeline *clutter_alpha_get_timeline (ClutterAlpha     *alpha);
 #define CLUTTER_ALPHA_SINE       clutter_sine_func
 /* FIXME add SINE_INC/DEC */
 #define CLUTTER_ALPHA_SQUARE     clutter_square_func
+#define CLUTTER_ALPHA_SMOOTHSTEP clutter_smoothstep_func
+
+#define CLUTTER_TYPE_SMOOTHSTEP (clutter_smoothstep_get_type ())
+
+typedef struct _ClutterSmoothstep  ClutterSmoothstep;
+
+struct _ClutterSmoothstep
+{
+  ClutterFixed min;
+  ClutterFixed max;
+};
+
+ClutterSmoothstep * clutter_smoothstep_copy    (const ClutterSmoothstep *smoothstep);
+
+void                clutter_smoothstep_free    (ClutterSmoothstep *smoothstep);
 
 guint32             clutter_ramp_inc_func      (ClutterAlpha     *alpha,
 						gpointer          dummy);
@@ -117,6 +134,8 @@ guint32          clutter_sine_func          (ClutterAlpha     *alpha,
 						gpointer          dummy);
 guint32             clutter_square_func        (ClutterAlpha     *alpha,
 						gpointer          dummy);
+guint32             clutter_smoothstep_func    (ClutterAlpha     *alpha,
+			                        gpointer         *data);
 
 G_END_DECLS
 

doc/reference/clutter-sections.txt

@@ -101,6 +101,9 @@ ClutterAlphaFunc
 clutter_alpha_set_func
 clutter_alpha_set_timeline
 clutter_alpha_get_timeline
+ClutterSmoothstep
+clutter_smoothstep_copy
+clutter_smoothstep_free
 CLUTTER_ALPHA_RAMP_INC
 clutter_ramp_inc_func
 CLUTTER_ALPHA_RAMP_DEC
@@ -111,6 +114,8 @@ CLUTTER_ALPHA_SINE
 clutter_sine_func
 CLUTTER_ALPHA_SQUARE
 clutter_square_func
+CLUTTER_ALPHA_SMOOTHSTEP
+clutter_smoothstep_func
 <SUBSECTION Standard>
 CLUTTER_ALPHA
 CLUTTER_IS_ALPHA

doc/reference/clutter.types

@@ -11,6 +11,7 @@ clutter_timeline_get_type
 clutter_media_get_type
 clutter_behaviour_get_type
 clutter_alpha_get_type
+clutter_smoothstep_get_type
 clutter_behaviour_bspline_get_type
 clutter_behaviour_ellipse_get_type
 clutter_behaviour_opacity_get_type

doc/reference/tmpl/clutter-alpha.sgml

@@ -123,6 +123,35 @@ transforming the current position in the timeline.
 @Returns: 
 
 
+<!-- ##### STRUCT ClutterSmoothstep ##### -->
+<para>
+Represents minimum and maximum thresholds for the smoothstep function. The
+thresholds are values from &lt;0,1&gt; relative to the frame-length of the behaviour,
+i.e., if the behaviour consists of 60 frames, threshold of 0.25 corresponds to
+frame 15, and threshold of 1.0 to frame 60.
+</para>
+
+@min: lower threshold; a #ClutterFixed value from &lt;0,1&gt;
+@max: upper threshold; a #ClutterFixed value from &lt;0,1&gt;
+
+
+<!-- ##### FUNCTION clutter_smoothstep_copy ##### -->
+<para>
+
+</para>
+
+@smoothstep: 
+@Returns: 
+
+
+<!-- ##### FUNCTION clutter_smoothstep_free ##### -->
+<para>
+
+</para>
+
+@smoothstep: 
+
+
 <!-- ##### MACRO CLUTTER_ALPHA_RAMP_INC ##### -->
 <para>
 Symbolic name for passing clutter_ramp_inc_func().