[gegl] spiral: a few improvements

[N/A <ell src gnome org>]

commit b2601ad641792e80f4174bd634bb84a2c93ccbf7
Author: Ell <ell_se yahoo com>
Date:   Wed Apr 19 12:16:47 2017 -0400

    spiral: a few improvements
    
    In particular, improve antialiasing about the origin, and adjust
    the start angle to compensate for the spiral's thickness, such that
    the central curve of the spiral remains fixed while the thickness
    changes.

 operations/workshop/spiral.c |   92 ++++++++++++++++++++++++++++++++---------
 1 files changed, 72 insertions(+), 20 deletions(-)
---
diff --git a/operations/workshop/spiral.c b/operations/workshop/spiral.c
index 9237a92..5c123a2 100644
--- a/operations/workshop/spiral.c
+++ b/operations/workshop/spiral.c
@@ -49,8 +49,15 @@ property_double (angle, _("Angle"), 0.0)
   value_range (0.0, 360.0)
   ui_meta     ("unit", "degree")
 
-property_boolean (clockwise, _("Clockwise"), TRUE)
-  description (_("Expand spiral clockwise"))
+enum_start (gegl_spiral_direction)
+  enum_value (GEGL_SPIRAL_DIRECTION_CLOCKWISE,        "cw",  N_("Clockwise"))
+  enum_value (GEGL_SPIRAL_DIRECTION_COUNTERCLOCKWISE, "ccw", N_("Counter-clockwise"))
+enum_end (GeglSpiralDirection)
+
+property_enum (direction, _("Direction"),
+               GeglSpiralDirection, gegl_spiral_direction,
+               GEGL_SPIRAL_DIRECTION_CLOCKWISE)
+  description (_("Spiral swirl direction"))
 
 property_color  (color1, _("Color 1"), "black")
   ui_meta     ("role", "color-primary")
@@ -141,9 +148,10 @@ process (GeglOperation       *operation,
   const Babl          *format    = babl_format ("R'G'B'A float");
   gfloat              *dest      = out_buf;
   gdouble              radius    = o->radius;
-  gdouble              lim       = radius * o->thickness;
-  gdouble              angle     = G_PI * o->angle / 180.0;
-  gboolean             clockwise = o->clockwise;
+  gdouble              thickness = o->thickness;
+  gdouble              angle     = o->angle / 360.0;
+  gboolean             clockwise = o->direction == GEGL_SPIRAL_DIRECTION_CLOCKWISE;
+  gdouble              lim;
   gfloat               color1[4];
   gfloat               color2[4];
   gdouble              x0;
@@ -152,24 +160,37 @@ process (GeglOperation       *operation,
   gint                 i;
   gint                 j;
 
-  gegl_color_get_pixel (o->color1, format, color1);
-  gegl_color_get_pixel (o->color2, format, color2);
+  if (thickness <= 0.5)
+    {
+      gegl_color_get_pixel (o->color1, format, color1);
+      gegl_color_get_pixel (o->color2, format, color2);
+    }
+  else
+    {
+      thickness  = 1.0 - thickness;
+      angle     -= 0.5;
+
+      gegl_color_get_pixel (o->color2, format, color1);
+      gegl_color_get_pixel (o->color1, format, color2);
+    }
 
-  if (radius == 1.0 || o->thickness == 0.0 || o->thickness == 1.0)
+  if (radius == 1.0 || thickness == 0.0)
     {
       gfloat color[4];
 
-      blend (color2, color1, o->thickness, color);
+      blend (color2, color1, thickness, color);
 
       gegl_memset_pattern (dest, color, sizeof (color), n_pixels);
 
       return TRUE;
     }
 
+  lim = thickness * radius;
+
   if (clockwise)
-    angle = G_PI - angle;
+    angle = 1.0 - angle;
 
-  angle += 2 * G_PI;
+  angle += thickness / 2.0;
 
   x0 = roi->x - gegl_coordinate_relative_to_pixel (o->x, o->width);
   y  = roi->y - gegl_coordinate_relative_to_pixel (o->y, o->height);
@@ -183,19 +204,50 @@ process (GeglOperation       *operation,
       for (i = roi->width; i; i--, x++)
         {
           gdouble x2 = x * x;
-          gdouble r  = sqrt (x2 + y2);
-          gdouble t  = atan2 (y, clockwise ? -x : x) + angle;
+          gdouble r;
+          gdouble t;
+          gdouble s;
           gdouble a;
-          gdouble l;
 
-          l = fmod (r + radius * t / (2.0 * G_PI), radius);
+          r = sqrt (x2 + y2);
+          t = atan2 (clockwise ? y : -y, x) / (2.0 * G_PI) - angle;
+
+          t = fmod (t + 2.0, 1.0);
+          s = t * radius;
+
+          if (r >= s)
+            {
+              r = fmod (r - s, radius);
 
-          if (l < 0.5)
-            a = MIN (lim, l + 0.5) + MAX (lim - (radius + l - 0.5), 0.0);
-          else if (l > radius - 0.5)
-            a = MAX (lim - l + 0.5, 0.0) + MIN (lim, l + 0.5 - radius);
+              if (r < 0.5)
+                a = MIN (lim, r + 0.5);
+              else if (r > radius - 0.5)
+                a = MAX (lim - (r - 0.5), 0.0) + MIN (lim, (r + 0.5) - radius);
+              else
+                a = CLAMP (lim - (r - 0.5), 0.0, 1.0);
+            }
           else
-            a = CLAMP (lim - l + 0.5, 0.0, 1.0);
+            {
+              gdouble l = lim - (radius - s);
+
+              if (t <= 0.5)
+                {
+                  if (r < 0.5)
+                    a = CLAMP (l + radius / 2.0, 0.0, 0.5 - r);
+                  else
+                    a = 0.0;
+                }
+              else
+                {
+                  if (r < 0.5)
+                    a = CLAMP (l, 0.0, r + 0.5);
+                  else
+                    a = CLAMP (l - (r - 0.5), 0.0, 1.0);
+                }
+
+              if (r > s - 0.5)
+                a += MIN (lim, (r + 0.5) - s);
+            }
 
           blend (color2, color1, a, dest);