[gegl] newsprint: improve symmetric dot pattern

[Øyvind Kolås <ok src gnome org>]

commit 54de27fde967f69437c9c2a58fee58286035d8cc
Author: Øyvind Kolås <pippin gimp org>
Date:   Sun Apr 23 15:54:56 2017 +0200

    newsprint: improve symmetric dot pattern
    
    there might still be gamma issues, but the pattern is now symmetric.

 operations/common/newsprint.c |   37 +++++++++++++++++++++++++++++++++++--
 1 files changed, 35 insertions(+), 2 deletions(-)
---
diff --git a/operations/common/newsprint.c b/operations/common/newsprint.c
index 2d1a627..f3121f6 100644
--- a/operations/common/newsprint.c
+++ b/operations/common/newsprint.c
@@ -179,9 +179,11 @@ float spachrotyze (
           float ay = fabsf (qphase ) ;
           float v = 0.0;
 
-          if  (ax + ay > 0.666)
+          if  (ax + ay > 1.0)
           {
-            v = 2.0 - sqrtf((1.0-ay) * (1.0-ay) + (1.0-ax) * (1.0-ax));
+            ay = 1.0 - ay;
+            ax = 1.0 - ax;
+            v = 2.0 - sqrtf (ay * ay + ax * ax);
           }
           else
           {
@@ -216,6 +218,37 @@ static inline double degrees_to_radians (double degrees)
   return degrees * (2 * G_PI / 360.0);
 }
 
+#if 0
+-- threshold filter
+
+level = 0.5
+
+for y=0, height-1 do
+       for x=0, width-1 do
+               ax = (x / width) * 2 - 1
+               ay = (y / height) * 2 - 1
+               if ax < 0 then ax = -ax end
+               if ay < 0 then ay = -ay end
+               v = ax * ay
+
+               if false then
+               if ax + ay > 1.0 then
+                 ax = 1.0 - ax
+                 ay = 1.0 - ay
+         --  v = (2.0 - math.sqrt((1.0-ay) * (1.0-ay) + (1.0-ax) * (1.0-ax)))/2
+          v = (math.sqrt(ax * ax + ay * ay)/2)
+
+               else
+          v = 1.0-math.sqrt(ax * ax + ay * ay)/2
+               end
+               end
+               set_value (x,y,v)
+       end
+       progress (y/height)
+end
+
+#endif
+
 
 static gboolean
 process (GeglOperation       *operation,