From 6e39efb9aaa1ed87b7320736ab08aabdbda4e4e1 Mon Sep 17 00:00:00 2001
From: Tomas Frydrych <tf@openedhand.com>
Date: Tue, 29 May 2007 09:21:18 +0000
Subject: [PATCH] fixed clutter cos functions; fixed tilt calculations in
 elliptic path

---
 ChangeLog                           | 15 +++++++++++
 clutter/clutter-behaviour-ellipse.c | 41 +++++++++++++----------------
 clutter/clutter-fixed.h             |  4 +--
 examples/behave.c                   |  2 +-
 4 files changed, 37 insertions(+), 25 deletions(-)

diff --git a/ChangeLog b/ChangeLog
index af3fa1b85..78d4f5fb4 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,18 @@
+2007-05-29  Tomas Frydrych  <tf@openedhand.com>
+
+	* clutter/clutter-fixed.h:
+	(clutter_cosx):
+	(clutter_cosi):
+	Fixed wrong sign in cos -> sin tranformation.
+
+	* clutter/clutter-behaviour-ellipse.c:
+	(clutter_behaviour_ellipse_advance):
+	Replaced coordinace calculation for tilted ellipse with a sane
+	algorithm.
+
+	* examples/behave.c:
+	Added tilt parameter to the example ellptic path.
+	
 2007-05-29  Tomas Frydrych  <tf@openedhand.com>
 
 	* clutter/cogl/gles/cogl.c:
diff --git a/clutter/clutter-behaviour-ellipse.c b/clutter/clutter-behaviour-ellipse.c
index bb1bef93c..f11a0ee9f 100644
--- a/clutter/clutter-behaviour-ellipse.c
+++ b/clutter/clutter-behaviour-ellipse.c
@@ -111,33 +111,30 @@ clutter_behaviour_ellipse_advance (ClutterBehaviourEllipse * e,
 
   if (e->priv->angle_tilt)
     {
-      /* Problem: sqrti is not giving us sufficient precission here
-       * and ClutterFixed range is too small to hold x^2+y^2 even for
-       * reasonable x, y values.
+      /*
+       * x2 = r * cos (angle + tilt)
+       * y2 = r * sin (angle + tilt)
+       *
+       * These can be trasformed to the formulas below using properties of
+       * sin (a + b) and cos (a + b)
        *
-       * We take advantage of sqrt (a * b^2) == sqrt (a) * b,
-       * and divide repeatedly by 4 until we get it into range, and then
-       * multiply the result by 2 the same number of times.
        */
-      ClutterFixed r;
-      guint q = x*x + y*y;
-      gint shift = 0;
+      ClutterFixed x2, y2;
 
-      while (q > G_MAXINT16)
-        {
-          ++shift;
-          
-          q >>= 2;
-        }
+      x2 = x * clutter_cosi (e->priv->angle_tilt) -
+        y * clutter_sini (e->priv->angle_tilt);
 
-      r = clutter_sqrtx (CLUTTER_INT_TO_FIXED (q)) << shift;
-
-      x = CFX_INT (CFX_MUL (r, clutter_cosi (angle + e->priv->angle_tilt)));
-      y = CFX_INT (CFX_MUL (r, clutter_sini (angle + e->priv->angle_tilt)));
+      y2 = y * clutter_cosi (e->priv->angle_tilt) +
+        x * clutter_sini (e->priv->angle_tilt);
+      
+      knot->x = CFX_INT (x2);
+      knot->y = CFX_INT (y2);
+    }
+  else
+    {
+      knot->x = x;
+      knot->y = y;
     }
-
-  knot->x = x;
-  knot->y = y;
   
 #if 0
    g_debug ("advancing to angle %d [%d, %d] (a: %d, b: %d)", 
diff --git a/clutter/clutter-fixed.h b/clutter/clutter-fixed.h
index 10bdfd659..d252bd3e9 100644
--- a/clutter/clutter-fixed.h
+++ b/clutter/clutter-fixed.h
@@ -171,7 +171,7 @@ ClutterFixed clutter_tani (ClutterAngle angle);
  *
  * Since: 0.2
  */
-#define clutter_cosx(angle) clutter_fixed_sin((angle) - CFX_PI_2)
+#define clutter_cosx(angle) clutter_fixed_sin((angle) + CFX_PI_2)
 
 /**
  * clutter_cosi:
@@ -188,7 +188,7 @@ ClutterFixed clutter_tani (ClutterAngle angle);
  *
  * Since: 0.2
  */
-#define clutter_cosi(angle) clutter_sini((angle) - 256)
+#define clutter_cosi(angle) clutter_sini((angle) + 256)
 
 ClutterFixed clutter_sqrtx (ClutterFixed x);
 gint         clutter_sqrti (gint         x);
diff --git a/examples/behave.c b/examples/behave.c
index 31a74bd6b..87718fa22 100644
--- a/examples/behave.c
+++ b/examples/behave.c
@@ -166,7 +166,7 @@ main (int argc, char *argv[])
     case PATH_ELLIPSE:
       p_behave =
 	clutter_behaviour_ellipse_new (alpha, 200, 200, 400, 300,
-				       0.0, 360.0, 0.0);
+				       0.0, 360.0, 120.0);
       break;
 
     case PATH_BSPLINE: