[sdf] Added function to get contour orientation.

* src/sdf/ftsdf.c (SDF_Contour_Orientation): Added
  enum to hold the different orientations of a contour.

* src/sdf/ftsdf.c (get_contour_orientation): Added
  function which can be used to compute the orientation
  of a contour.

* src/sdf/ftbsdf.c (*): Remove completed `[TODO]'s.

[GSoC]ChangeLog

@@ -1,3 +1,16 @@
+2020-08-6  Anuj Verma  <anujv@iitbhilai.ac.in>
+
+	[sdf] Added function to get contour orientation.
+
+	* src/sdf/ftsdf.c (SDF_Contour_Orientation): Added
+	  enum to hold the different orientations of a contour.
+
+	* src/sdf/ftsdf.c (get_contour_orientation): Added
+	  function which can be used to compute the orientation
+	  of a contour.
+
+	* src/sdf/ftbsdf.c (*): Remove completed `[TODO]'s.
+
 2020-08-6  Anuj Verma  <anujv@iitbhilai.ac.in>
 
 	[sdf -> bsdf] Added documentation for functions of the `bsdf' renderer.

src/sdf/ftbsdf.c

@@ -308,7 +308,6 @@
     /* approximate direction of the edge, we can    */
     /* approximate the edge distance much better.   */
 
-    /* [TODO]: Add squared distance support. */
     if ( g.x == 0 || g.y == 0 )
       dist = ONE / 2 - alphas[4];
     else
@@ -509,7 +508,6 @@
     /*         convert the source bitmap to desired bpp.        */
     switch ( source->pixel_mode ) {
     case FT_PIXEL_MODE_MONO:
-      /* [TODO] */
     {
       FT_Int  t_width = worker->width;
       FT_Int  t_rows  = worker->rows;

src/sdf/ftsdf.c

@@ -151,7 +151,7 @@
    *
    */
 
-  #define MUL_26D6( a, b ) ( ( a * b ) / 64 )
+  #define MUL_26D6( a, b ) ( ( ( a ) * ( b ) ) / 64 )
   #define VEC_26D6_DOT( p, q ) ( MUL_26D6( p.x, q.x ) +   \
                                  MUL_26D6( p.y, q.y ) )
 
@@ -177,6 +177,16 @@
 
   } SDF_Edge_Type;
 
+  /* Enumeration for the orientation of a contour, remember */
+  /* the orientation is independent of the fill rule.       */
+  typedef enum  SDF_Contour_Orientation_
+  {
+    SDF_ORIENTATION_NONE  = 0,  /* undefined, used to initialize */
+    SDF_ORIENTATION_CW    = 0,  /* clockwise orientation         */
+    SDF_ORIENTATION_ACW   = 0,  /* anti-clockwise orientation    */
+
+  } SDF_Contour_Orientation;
+
   /* represent a single edge in a contour */
   typedef struct  SDF_Edge_
   {
@@ -694,6 +704,67 @@
     return cbox;
   }
 
+  /* The function returns the orientation for a single contour.  */
+  /* Note that the orientation is independent of the fill rule.  */
+  /* So, for ttf the clockwise has to be filled and the opposite */
+  /* for otf fonts.                                              */
+  static SDF_Contour_Orientation
+  get_contour_orientation ( SDF_Contour*  contour )
+  {
+    SDF_Edge*  head = NULL;
+    FT_26D6    area = 0;
+
+
+    /* return none if invalid parameters */
+    if ( !contour || !contour->edges )
+      return SDF_ORIENTATION_NONE;
+
+    head = contour->edges;
+
+    /* Simply calculate the area of the control box for */
+    /* all the edges.                                   */
+    while ( head )
+    {
+      switch ( head->edge_type ) {
+      case SDF_EDGE_LINE:
+      {
+        area += MUL_26D6( ( head->end_pos.x - head->start_pos.x ),
+                          ( head->end_pos.y + head->start_pos.y ) );
+        break;
+      }
+      case SDF_EDGE_CONIC:
+      {
+        area += MUL_26D6( head->control_a.x - head->start_pos.x,
+                          head->control_a.y + head->start_pos.y );
+        area += MUL_26D6( head->end_pos.x - head->control_a.x,
+                          head->end_pos.y + head->control_a.y );
+        break;
+      }
+      case SDF_EDGE_CUBIC:
+      {
+        area += MUL_26D6( head->control_a.x - head->start_pos.x,
+                          head->control_a.y + head->start_pos.y );
+        area += MUL_26D6( head->control_b.x - head->control_a.x,
+                          head->control_b.y + head->control_a.y );
+        area += MUL_26D6( head->end_pos.x - head->control_b.x,
+                          head->end_pos.y + head->control_b.y );
+        break;
+      }
+      default:
+          return SDF_ORIENTATION_NONE;
+      }
+
+      head = head->next;
+    }
+
+    /* Clockwise contour cover a positive area, and Anti-Clockwise */
+    /* contour cover a negitive area.                              */
+    if ( area > 0 )
+      return SDF_ORIENTATION_CW;
+    else
+      return SDF_ORIENTATION_ACW;
+  }
+
   /* The function is exactly same as the one    */
   /* in the smooth renderer. It splits a conic  */
   /* into two conic exactly half way at t = 0.5 */