[gimp] Bug 781804 - Dodge/Burn tool produces artifacts with negative channel values

[N/A <ell src gnome org>]

commit e0dcf538e5381fa6349036d43f02fafd52d87cb3
Author: Ell <ell_se yahoo com>
Date:   Wed Apr 26 21:25:51 2017 -0400

    Bug 781804 - Dodge/Burn tool produces artifacts with negative channel values
    
    The halftones transfer mode of dodge/burn uses pow(), which produces
    NaN for negative input values.  This tool doesn't really have OOG
    values in mind, but using an odd power function fixes this issue,
    and is in line with the behavior of the other modes w.r.t. OOG
    values.

 app/gegl/gimp-gegl-loops.c |   16 +++++++++++++---
 1 files changed, 13 insertions(+), 3 deletions(-)
---
diff --git a/app/gegl/gimp-gegl-loops.c b/app/gegl/gimp-gegl-loops.c
index 87aad49..1824cdc 100644
--- a/app/gegl/gimp-gegl-loops.c
+++ b/app/gegl/gimp-gegl-loops.c
@@ -216,6 +216,16 @@ gimp_gegl_convolve (GeglBuffer          *src_buffer,
   g_free (src);
 }
 
+static inline gfloat
+odd_powf (gfloat x,
+          gfloat y)
+{
+  if (x >= 0.0f)
+    return  powf ( x, y);
+  else
+    return -powf (-x, y);
+}
+
 void
 gimp_gegl_dodgeburn (GeglBuffer          *src_buffer,
                      const GeglRectangle *src_rect,
@@ -276,9 +286,9 @@ gimp_gegl_dodgeburn (GeglBuffer          *src_buffer,
 
           while (count--)
             {
-              *dest++ = pow (*src++, factor);
-              *dest++ = pow (*src++, factor);
-              *dest++ = pow (*src++, factor);
+              *dest++ = odd_powf (*src++, factor);
+              *dest++ = odd_powf (*src++, factor);
+              *dest++ = odd_powf (*src++, factor);
 
               *dest++ = *src++;
             }