[gegl] panorama-projection: use scale matrix for near nadir/zenith

[Øyvind Kolås <ok src gnome org>]

commit 069810a4319080c74a066fb4ad578106a7a0c227
Author: Øyvind Kolås <pippin gimp org>
Date:   Wed Apr 11 18:42:22 2018 +0200

    panorama-projection: use scale matrix for near nadir/zenith
    
    We are skipping the computation of the shape of the pixel neighborhood to
    include samples for when not needed since this is quite expensive. This commit
    limits the tilt angle range of the optimization to where it is valid.

 operations/common/panorama-projection.c |   44 ++++++++++++++++++------------
 1 files changed, 26 insertions(+), 18 deletions(-)
---
diff --git a/operations/common/panorama-projection.c b/operations/common/panorama-projection.c
index 78cadd5..d0cd97d 100644
--- a/operations/common/panorama-projection.c
+++ b/operations/common/panorama-projection.c
@@ -445,9 +445,10 @@ process (GeglOperation       *operation,
   }
 
   if (sampler_type != GEGL_SAMPLER_NEAREST &&
-      !(o->little_planet == FALSE && o->inverse == FALSE)) // for forward transforms of non-little planet we
-                                                           // skip the inverse scale paths, since they are 
unlikely to be needed
-                                                           // and slow thing down
+      !(o->little_planet == FALSE && o->inverse == FALSE &&
+      fabs(o->tilt < 33)))
+    /* skip the computation of sampler neighborhood scale matrix in cases where
+     * we are unlikely to be scaling down */
     scale = &scale_matrix;
   else
     format_io = babl_format ("RGBA float");
@@ -490,12 +491,12 @@ process (GeglOperation       *operation,
   float ax, ay, bx, by;                                  \
   gegl_unmap(x + 0.5 * ud, y, ax, ay);                   \
   gegl_unmap(x - 0.5 * ud, y, bx, by);                   \
-  matrix.coeff[0][0] = (ax - bx) * transform.in_width;   \
-  matrix.coeff[1][0] = (ay - by) * transform.in_height;  \
+  matrix.coeff[0][0] = (ax - bx);   \
+  matrix.coeff[1][0] = (ay - by);  \
   gegl_unmap(x, y + 0.5 * ud, ax, ay);                   \
   gegl_unmap(x, y - 0.5 * ud, bx, by);                   \
-  matrix.coeff[0][1] = (ax - bx) * transform.in_width;   \
-  matrix.coeff[1][1] = (ay - by) * transform.in_height;  \
+  matrix.coeff[0][1] = (ax - bx);   \
+  matrix.coeff[1][1] = (ay - by);  \
 }
 
 #define gegl_unmap(xx,yy,ud,vd) {                                  \
@@ -506,22 +507,29 @@ process (GeglOperation       *operation,
                 gegl_unmap(u,v, cx, cy);
 #undef gegl_unmap
 
-#if 0
-                // special handling across pan-horizon, maybe there
-                // is more special cases needing handling as well
-                if (scale_matrix.coeff[0][0] > transform.in_width/2)
-                  scale_matrix.coeff[0][0] -= transform.in_width;
-                if (scale_matrix.coeff[0][0] < -transform.in_width/2)
-                  scale_matrix.coeff[0][0] += transform.in_width;
-                if (scale_matrix.coeff[0][1] > transform.in_width/2)
-                  scale_matrix.coeff[0][1] -= transform.in_width;
-                if (scale_matrix.coeff[0][1] < -transform.in_width/2)
-                  scale_matrix.coeff[0][1] += transform.in_width;
+#if 1
+                if (scale_matrix.coeff[0][0] > 0.5f)
+                  scale_matrix.coeff[0][0] = (scale_matrix.coeff[0][0]-1.0) * transform.in_width;
+                else if (scale_matrix.coeff[0][0] < -0.5f) 
+                  scale_matrix.coeff[0][0] = (scale_matrix.coeff[0][0]+1.0) * transform.in_width;
+                else
+                  scale_matrix.coeff[0][0] *= transform.in_width;
+
+                if (scale_matrix.coeff[0][1] > 0.5f)
+                  scale_matrix.coeff[0][1] = (scale_matrix.coeff[0][1]-1.0) * transform.in_width;
+                else if (scale_matrix.coeff[0][1] < -0.5f)
+                  scale_matrix.coeff[0][1] = (scale_matrix.coeff[0][1]+1.0) * transform.in_width;
+                else
+                  scale_matrix.coeff[0][1] *= transform.in_width;
+
+                scale_matrix.coeff[1][1] *= transform.in_height;
+                scale_matrix.coeff[1][0] *= transform.in_height;
 #endif
                 getfun (sampler,
                         cx * transform.in_width + 0.5f,
                         cy * transform.in_height + 0.5f,
                         scale, out, abyss_mode);
+
                 out += 4;
 
                 /* update x, y and u,v coordinates */