[gegl] spherize: rename "amount" to "curvature"; add separate "amount" prop

[N/A <ell src gnome org>]

commit ac86c341cc92b65bd2037bef55e2194d14e0ba51
Author: Ell <ell_se yahoo com>
Date:   Tue Oct 3 07:45:51 2017 -0400

    spherize: rename "amount" to "curvature"; add separate "amount" prop
    
    Rename the "amount" property to "curvature" (which better conveys
    its function).  Negative curvatures apply the transformation using
    a concave spherical cap, having the same curvature as the convex
    cap of the corresponding positive curvature (restoring the original
    behavior).  Negative curvatures might be dropped later, especially
    since they produce the same result as positive curvatures when the
    angle of view is 0.
    
    Add a separate "amount" property, which controls the scale factor
    for the displacement (as in Photoshop).  Positive amounts use the
    forward mapping, while negative amounts use the inverse mapping.

 operations/workshop/spherize.c |   26 +++++++++++++++++++-------
 1 files changed, 19 insertions(+), 7 deletions(-)
---
diff --git a/operations/workshop/spherize.c b/operations/workshop/spherize.c
index c465ca6..30c113d 100644
--- a/operations/workshop/spherize.c
+++ b/operations/workshop/spherize.c
@@ -38,10 +38,14 @@ property_double (angle_of_view, _("Angle of view"), 0.0)
   value_range (0.0, 180.0)
   ui_meta ("unit", "degree")
 
-property_double (amount, _("Amount"), 1.0)
+property_double (curvature, _("Curvature"), 1.0)
   description (_("Spherical cap apex angle, as a fraction of the co-angle of view"))
   value_range (-1.0, 1.0)
 
+property_double (amount, _("Amount"), 1.0)
+  description (_("Displacement scaling factor (negative values refer to the inverse displacement)"))
+  value_range (-1.0, 1.0)
+
 property_enum (sampler_type, _("Resampling method"),
   GeglSamplerType, gegl_sampler_type, GEGL_SAMPLER_LINEAR)
   description(_("Mathematical method for reconstructing pixel values"))
@@ -71,7 +75,7 @@ is_identity (GeglOperation *operation)
 {
   GeglProperties *o = GEGL_PROPERTIES (operation);
 
-  return fabs (o->amount) < EPSILON;
+  return fabs (o->curvature) < EPSILON || fabs (o->amount) < EPSILON;
 }
 
 static gboolean
@@ -167,10 +171,12 @@ process (GeglOperation       *operation,
   gdouble              dx = 0.0, dy = 0.0;
   gdouble              coangle_of_view_2;
   gdouble              focal_length;
+  gdouble              curvature_sign;
   gdouble              cap_angle_2;
   gdouble              cap_radius;
   gdouble              cap_depth;
-  gdouble              f, f2, r, r_inv, r2, p, f_p, f_p2, f_pf, a, a_inv;
+  gdouble              factor;
+  gdouble              f, f2, r, r_inv, r2, p, f_p, f_p2, f_pf, a, a_inv, sgn;
   gboolean             is_id;
   gboolean             perspective;
   gboolean             inverse;
@@ -205,9 +211,11 @@ process (GeglOperation       *operation,
 
   coangle_of_view_2 = MAX (180.0 - o->angle_of_view, 0.01) * G_PI / 360.0;
   focal_length      = tan (coangle_of_view_2);
-  cap_angle_2       = fabs (o->amount) * coangle_of_view_2;
+  curvature_sign    = o->curvature > 0.0 ? +1.0 : -1.0;
+  cap_angle_2       = fabs (o->curvature) * coangle_of_view_2;
   cap_radius        = 1.0 / sin (cap_angle_2);
-  cap_depth         = cap_radius * cos (cap_angle_2);
+  cap_depth         = curvature_sign * cap_radius * cos (cap_angle_2);
+  factor            = fabs (o->amount);
 
   f     = focal_length;
   f2    = f * f;
@@ -220,6 +228,7 @@ process (GeglOperation       *operation,
   f_pf  = f_p * f;
   a     = cap_angle_2;
   a_inv = 1 / a;
+  sgn   = curvature_sign;
 
   is_id       = is_identity (operation);
   perspective = o->angle_of_view > EPSILON;
@@ -254,7 +263,7 @@ process (GeglOperation       *operation,
                       gdouble d2_f2 = d2 + f2;
 
                       if (perspective)
-                        src_d = (f_pf - sqrt (d2_f2 * r2 - f_p2 * d2)) * d / d2_f2;
+                        src_d = (f_pf - sgn * sqrt (d2_f2 * r2 - f_p2 * d2)) * d / d2_f2;
 
                       src_d = (G_PI_2 - acos (src_d * r_inv)) * a_inv;
                     }
@@ -263,9 +272,12 @@ process (GeglOperation       *operation,
                       src_d = r * cos (G_PI_2 - src_d * a);
 
                       if (perspective)
-                        src_d = f * src_d / (f_p - sqrt (r2 - src_d * src_d));
+                        src_d = f * src_d / (f_p - sgn * sqrt (r2 - src_d * src_d));
                     }
 
+                  if (factor < 1.0)
+                    src_d = d + (src_d - d) * factor;
+
                   src_x = dx ? cx + src_d * x / (dx * d) :
                                i + 0.5;
                   src_y = dy ? cy + src_d * y / (dy * d) :