[clutter] actor: Fix transforming stage point when scale is less than 1

[Jonas Ådahl <jadahl src gnome org>]

commit 5d83260b19c06f216cfdb21a57f256ebee1affef
Author: Jonas Ådahl <jadahl gmail com>
Date:   Thu Sep 10 16:12:51 2015 +0800

    actor: Fix transforming stage point when scale is less than 1
    
    The commit 6cd24faaa54de3246ca45d1c7426d8b7a74f71db (actor: Clean up
    transform_stage_point()) changed the validation of the transformation
    matrix to ignore the fraction part of the determinant. This caused
    clutter_actor_transform_stage_point() to fail and return FALSE for
    actors which scale was less than 1.
    
    Previously the validation was ('det' being a float):
        det = (RQ[0][0] * ST[0][0])
            + (RQ[0][1] * ST[0][1])
            + (RQ[0][2] * ST[0][2]);
        if (!det)
                return FALSE;
    
    Semantically, the if statement expression '!det' is equivalent to
    'det == 0', i.e. 'det == 0.0f'. Post cleanup patches, 'det' was turned
    into a double, and the if statement was changed to:
    
        if (CLUTTER_NEARBYINT (det) == 0)
                return FALSE;
    
    which, different from before, rounds the determinant to the nearest
    integer value, meaning determinant in the range (-0.5, 0.5) would be
    considered invalid.
    
    This patch reverts this part to the old behavior, while, because of the
    inexact nature of floating point arithmetics, allowing a bit more liberal
    meaning of "equals to 0" than '== 0.0'.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=754766

 clutter/clutter-actor.c |    6 +++---
 1 files changed, 3 insertions(+), 3 deletions(-)
---
diff --git a/clutter/clutter-actor.c b/clutter/clutter-actor.c
index 1cbbd5c..ad106c4 100644
--- a/clutter/clutter-actor.c
+++ b/clutter/clutter-actor.c
@@ -15190,8 +15190,8 @@ clutter_actor_transform_stage_point (ClutterActor *self,
       dy2 = v[2].y - v[3].y;
 
       det = DET (dx1, dx2, dy1, dy2);
-      if (CLUTTER_NEARBYINT (det) == 0)
-       return FALSE;
+      if (fabs (det) <= DBL_EPSILON)
+        return FALSE;
 
       RQ[0][2] = DET (px, dx2, py, dy2) / det;
       RQ[1][2] = DET (dx1, px, dy1, py) / det;
@@ -15236,7 +15236,7 @@ clutter_actor_transform_stage_point (ClutterActor *self,
   det = (RQ[0][0] * ST[0][0])
       + (RQ[0][1] * ST[0][1])
       + (RQ[0][2] * ST[0][2]);
-  if (CLUTTER_NEARBYINT (det) == 0)
+  if (fabs (det) <= DBL_EPSILON)
     return FALSE;
 
   /*