[sdf -> bsdf] Added edge detection algorithm.

Added edge detection algorithm. It works by checking
the neighboring pixels and if any neighbor is not
filled (i.e. belongs to background) we mark the
pixel as edge by setting it's distance to 0.

* src/sdf/ftbsdf.c (bsdf_is_edge): Added function to
  detect if the pixel is an edge.

2 files changed, 106 insertions, 3 deletions

diff --git a/[GSoC]ChangeLog b/[GSoC]ChangeLog
index ae4cae034..9d15fea09 100644
--- a/[GSoC]ChangeLog
+++ b/[GSoC]ChangeLog
@@ -1,5 +1,17 @@
 2020-07-27  Anuj Verma  <anujv@iitbhilai.ac.in>
 
+	[sdf -> bsdf] Added edge detection algorithm.
+
+	Added edge detection algorithm. It works by checking
+	the neighboring pixels and if any neighbor is not
+	filled (i.e. belongs to background) we mark the
+	pixel as edge by setting it's distance to 0.
+
+	* src/sdf/ftbsdf.c (bsdf_is_edge): Added function to
+	  detect if the pixel is an edge.
+
+2020-07-27  Anuj Verma  <anujv@iitbhilai.ac.in>
+
 	[sdf -> bsdf] Added the second pass of the '8SED'.
 
 	Added the second pass of the 8SED algorithm. The second pass
diff --git a/src/sdf/ftbsdf.c b/src/sdf/ftbsdf.c
index caa1acfb5..004346a04 100644
--- a/src/sdf/ftbsdf.c
+++ b/src/sdf/ftbsdf.c
@@ -85,6 +85,94 @@
   /**************************************************************************
    *
    * @Function:
+   *   bsdf_is_edge
+   *
+   * @Description:
+   *   [TODO]
+   *
+   * @Input:
+   *   [TODO]
+   *
+   * @Return:
+   *   [TODO]
+   */
+  static FT_Bool
+  bsdf_is_edge( FT_Byte*  s,    /* source bitmap             */
+                FT_Int    x,    /* x index of point to check */
+                FT_Int    y,    /* y index of point to check */
+                FT_Int    w,    /* width                     */
+                FT_Int    r )   /* rows                      */
+  {
+    FT_Bool   is_edge       = 0;
+    FT_Byte*  to_check      = NULL;
+    FT_Int    num_neighbour = 0;
+
+    if ( y == 7 && x == 20 )
+      to_check = NULL;
+
+    if ( *s == 0 )
+      goto Done;
+
+    /* up */
+    if ( y > 0 )
+    {
+      num_neighbour++;
+      to_check = s -  w;
+      if ( *to_check == 0 )
+      {
+        is_edge = 1;
+        goto Done;
+      }
+    }
+
+    /* down */
+    if ( y < r - 2 )
+    {
+      num_neighbour++;
+      to_check = s + w;
+      if ( *to_check == 0 )
+      {
+        is_edge = 1;
+        goto Done;
+      }
+    }
+
+    /* left */
+    if ( x > 0 )
+    {
+      num_neighbour++;
+      to_check = s - 1;
+      if ( *to_check == 0 )
+      {
+        is_edge = 1;
+        goto Done;
+      }
+    }
+
+    /* right */
+    if ( x < w - 2 )
+    {
+      num_neighbour++;
+      to_check = s + 1;
+      if ( *to_check == 0 )
+      {
+        is_edge = 1;
+        goto Done;
+      }
+    }
+
+    
+
+    if ( num_neighbour != 4 )
+      is_edge = 1;
+
+  Done:
+    return is_edge;
+  }
+
+  /**************************************************************************
+   *
+   * @Function:
    *   bsdf_init_distance_map
    *
    * @Description:
@@ -233,19 +321,22 @@
           pixel_value <<= 8;
 
   #else
-          if ( pixel_value )
+          if ( bsdf_is_edge( s + s_index , s_i, s_j, s_width, s_rows ) )
           {
             t[t_index].dist = 0;
-            t[t_index].sign = 1;
           }
           else
           {
             t[t_index].near.x = FT_INT_MAX;
             t[t_index].near.y = FT_INT_MAX;
             t[t_index].dist   = 128 * ONE;
-            t[t_index].sign   = -1;
           }
 
+          if ( pixel_value )
+            t[t_index].sign = 1;
+          else
+            t[t_index].sign = -1;
+
   #endif
         }
       }