[gegl] transform: make inverse jacobian for perspective accurate

[Ãyvind KolÃs <ok src gnome org>]

commit 365fef7ea04e6652778d9b73d2081463bf974c1e
Author: Ãyvind KolÃs <pippin gimp org>
Date:   Sun Apr 8 20:18:42 2012 +0200

    transform: make inverse jacobian for perspective accurate

 operations/transform/transform-core.c |    9 +++++----
 1 files changed, 5 insertions(+), 4 deletions(-)
---
diff --git a/operations/transform/transform-core.c b/operations/transform/transform-core.c
index ff927f4..31ae3e0 100644
--- a/operations/transform/transform-core.c
+++ b/operations/transform/transform-core.c
@@ -20,6 +20,7 @@
  *           2011 Mikael Magnusson
  *           2011 Massimo Valentini
  *           2012 Kevin Cozens
+ *           2012 Nicolas Robidoux
  */
 
 /* TODO: only calculate pixels inside transformed polygon */
@@ -787,10 +788,10 @@ affine_generic (GeglBuffer  *dest,
               float u = u_float / w_float;
               float v = v_float / w_float;
 
-              inverse_jacobian.coeff[0][0]= (u_float + inverse.coeff[0][0] ) / (w_float + inverse.coeff[2][0]) - u;
-              inverse_jacobian.coeff[0][1]= (u_float + inverse.coeff[0][1] ) / (w_float + inverse.coeff[2][1]) - u;
-              inverse_jacobian.coeff[1][0]= (v_float + inverse.coeff[1][0] ) / (w_float + inverse.coeff[2][0]) - v;
-              inverse_jacobian.coeff[1][1]= (v_float + inverse.coeff[1][1] ) / (w_float + inverse.coeff[2][1]) - v;
+              inverse_jacobian.coeff[0][0] = (inverse.coeff[0][0] - inverse.coeff[2][0] * u) / w_float;
+              inverse_jacobian.coeff[0][1] = (inverse.coeff[0][1] - inverse.coeff[2][1] * u) / w_float;
+              inverse_jacobian.coeff[1][0] = (inverse.coeff[1][0] - inverse.coeff[2][0] * v) / w_float;
+              inverse_jacobian.coeff[1][1] = (inverse.coeff[1][1] - inverse.coeff[2][1] * v) / w_float;
 
               gegl_sampler_get (sampler, u, v, &inverse_jacobian, dest_ptr);
               dest_ptr+=4;