[gegl] sobel: Bring OpenCL implementation closer to the C one

[Mukund Sivaraman <muks src gnome org>]

commit 8feb4eb0f2e19bbace2e5e6fd348dd44b168d7aa
Author: Mukund Sivaraman <muks banu com>
Date:   Thu Oct 9 16:16:01 2014 +0530

    sobel: Bring OpenCL implementation closer to the C one
    
    There is still the case of removing the sobel radius and access out
    of rect bounds.

 opencl/edge-sobel.cl   |   17 ++++++++---------
 opencl/edge-sobel.cl.h |   17 ++++++++---------
 2 files changed, 16 insertions(+), 18 deletions(-)
---
diff --git a/opencl/edge-sobel.cl b/opencl/edge-sobel.cl
index c41a290..f6ca9d1 100644
--- a/opencl/edge-sobel.cl
+++ b/opencl/edge-sobel.cl
@@ -32,23 +32,22 @@ kernel void kernel_edgesobel(global float4 *in,
     if (horizontal)
     {
         hor_grad +=
-            - 1.0f * pix_fl + 1.0f * pix_fr
-            - 2.0f * pix_ml + 2.0f * pix_mr
-            - 1.0f * pix_bl + 1.0f * pix_br;
+            (-1.0f * pix_fl + 1.0f * pix_fr) +
+            (-2.0f * pix_ml + 2.0f * pix_mr) +
+            (-1.0f * pix_bl + 1.0f * pix_br);
     }
     if (vertical)
     {
         ver_grad +=
-            - 1.0f * pix_fl - 2.0f * pix_fm
-            - 1.0f * pix_fr + 1.0f * pix_bl
-            + 2.0f * pix_bm + 1.0f * pix_br;
+            ( 1.0f * pix_fl) + ( 2.0f * pix_fm) + ( 1.0f * pix_fr) +
+            (-1.0f * pix_bl) + (-2.0f * pix_bm) + (-1.0f * pix_br);
     }
 
     if (horizontal && vertical)
     {
-        gradient = sqrt(
-            hor_grad * hor_grad +
-            ver_grad * ver_grad) / 1.41f;
+        /* sqrt(32.0) = 5.656854249492381 */
+        gradient = sqrt(hor_grad * hor_grad +
+                        ver_grad * ver_grad) / 5.656854249492381;
     }
     else
     {
diff --git a/opencl/edge-sobel.cl.h b/opencl/edge-sobel.cl.h
index 2dc5b0c..5f6fe7c 100644
--- a/opencl/edge-sobel.cl.h
+++ b/opencl/edge-sobel.cl.h
@@ -33,23 +33,22 @@ static const char* edge_sobel_cl_source =
 "    if (horizontal)                                                           \n"
 "    {                                                                         \n"
 "        hor_grad +=                                                           \n"
-"            - 1.0f * pix_fl + 1.0f * pix_fr                                   \n"
-"            - 2.0f * pix_ml + 2.0f * pix_mr                                   \n"
-"            - 1.0f * pix_bl + 1.0f * pix_br;                                  \n"
+"            (-1.0f * pix_fl + 1.0f * pix_fr) +                                \n"
+"            (-2.0f * pix_ml + 2.0f * pix_mr) +                                \n"
+"            (-1.0f * pix_bl + 1.0f * pix_br);                                 \n"
 "    }                                                                         \n"
 "    if (vertical)                                                             \n"
 "    {                                                                         \n"
 "        ver_grad +=                                                           \n"
-"            - 1.0f * pix_fl - 2.0f * pix_fm                                   \n"
-"            - 1.0f * pix_fr + 1.0f * pix_bl                                   \n"
-"            + 2.0f * pix_bm + 1.0f * pix_br;                                  \n"
+"            ( 1.0f * pix_fl) + ( 2.0f * pix_fm) + ( 1.0f * pix_fr) +          \n"
+"            (-1.0f * pix_bl) + (-2.0f * pix_bm) + (-1.0f * pix_br);           \n"
 "    }                                                                         \n"
 "                                                                              \n"
 "    if (horizontal && vertical)                                               \n"
 "    {                                                                         \n"
-"        gradient = sqrt(                                                      \n"
-"            hor_grad * hor_grad +                                             \n"
-"            ver_grad * ver_grad) / 1.41f;                                     \n"
+"        /* sqrt(32.0) = 5.656854249492381 */                                  \n"
+"        gradient = sqrt(hor_grad * hor_grad +                                 \n"
+"                        ver_grad * ver_grad) / 5.656854249492381;             \n"
 "    }                                                                         \n"
 "    else                                                                      \n"
 "    {                                                                         \n"