[freetype2] GSoC-2020-anuj 4dc90dc 1/3: [sdf] Added utility functions for contours.

[Anuj Verma]

branch: GSoC-2020-anuj
commit 4dc90dc8d053a830e104126618069de49fc94087
Author: Anuj Verma <anujv@iitbhilai.ac.in>
Commit: Anuj Verma <anujv@iitbhilai.ac.in>

    [sdf] Added utility functions for contours.
    
    * src/sdf/ftsdf.c (get_control_box, get_contour_orientation): Added 
functions to
      get control box and orientation of any `SDF_Contour'.
    
    * src/sdf/ftsdf.c (split_sdf_shape): Added function to split a complete 
shape (i.e.
      a collection of contours) into a number of small lines.
---
 src/sdf/ftsdf.c | 454 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 454 insertions(+)

diff --git a/src/sdf/ftsdf.c b/src/sdf/ftsdf.c
index 9aba0f5..61611f2 100644
--- a/src/sdf/ftsdf.c
+++ b/src/sdf/ftsdf.c
@@ -797,4 +797,458 @@
     return error;
   }
 
+  /**************************************************************************
+   *
+   * utility functions
+   *
+   */
+
+  /* The function returns the control box of a edge. */
+  /* The control box is a rectangle in which all the */
+  /* control points can fit tightly.                 */
+  static FT_CBox
+  get_control_box( SDF_Edge  edge )
+  {
+    FT_CBox  cbox;
+    FT_Bool  is_set = 0;
+
+
+    switch (edge.edge_type) {
+    case SDF_EDGE_CUBIC:
+    {
+      cbox.xMin = edge.control_b.x;
+      cbox.xMax = edge.control_b.x;
+      cbox.yMin = edge.control_b.y;
+      cbox.yMax = edge.control_b.y;
+
+      is_set = 1;
+    }
+    case SDF_EDGE_CONIC:
+    {
+      if ( is_set )
+      {
+        cbox.xMin = edge.control_a.x < cbox.xMin ?
+                    edge.control_a.x : cbox.xMin;
+        cbox.xMax = edge.control_a.x > cbox.xMax ?
+                    edge.control_a.x : cbox.xMax;
+
+        cbox.yMin = edge.control_a.y < cbox.yMin ?
+                    edge.control_a.y : cbox.yMin;
+        cbox.yMax = edge.control_a.y > cbox.yMax ?
+                    edge.control_a.y : cbox.yMax;
+      }
+      else
+      {
+        cbox.xMin = edge.control_a.x;
+        cbox.xMax = edge.control_a.x;
+        cbox.yMin = edge.control_a.y;
+        cbox.yMax = edge.control_a.y;
+
+        is_set = 1;
+      }
+    }
+    case SDF_EDGE_LINE:
+    {
+      if ( is_set )
+      {
+        cbox.xMin = edge.start_pos.x < cbox.xMin ?
+                    edge.start_pos.x : cbox.xMin;
+        cbox.xMax = edge.start_pos.x > cbox.xMax ?
+                    edge.start_pos.x : cbox.xMax;
+
+        cbox.yMin = edge.start_pos.y < cbox.yMin ?
+                    edge.start_pos.y : cbox.yMin;
+        cbox.yMax = edge.start_pos.y > cbox.yMax ?
+                    edge.start_pos.y : cbox.yMax;
+      }
+      else
+      {
+        cbox.xMin = edge.start_pos.x;
+        cbox.xMax = edge.start_pos.x;
+        cbox.yMin = edge.start_pos.y;
+        cbox.yMax = edge.start_pos.y;
+      }
+
+      cbox.xMin = edge.end_pos.x < cbox.xMin ?
+                  edge.end_pos.x : cbox.xMin;
+      cbox.xMax = edge.end_pos.x > cbox.xMax ?
+                  edge.end_pos.x : cbox.xMax;
+
+      cbox.yMin = edge.end_pos.y < cbox.yMin ?
+                  edge.end_pos.y : cbox.yMin;
+      cbox.yMax = edge.end_pos.y > cbox.yMax ?
+                  edge.end_pos.y : cbox.yMax;
+
+      break;
+    }
+    default:
+        break;
+    }
+
+    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 */
+  static void
+  split_conic( FT_26D6_Vec*  base )
+  {
+    FT_26D6  a, b;
+
+
+    base[4].x = base[2].x;
+    a = base[0].x + base[1].x;
+    b = base[1].x + base[2].x;
+    base[3].x = b / 2;
+    base[2].x = ( a + b ) / 4;
+    base[1].x = a / 2;
+
+    base[4].y = base[2].y;
+    a = base[0].y + base[1].y;
+    b = base[1].y + base[2].y;
+    base[3].y = b / 2;
+    base[2].y = ( a + b ) / 4;
+    base[1].y = a / 2;
+  }
+
+  /* The function is exactly same as the one    */
+  /* in the smooth renderer. It splits a cubic  */
+  /* into two cubic exactly half way at t = 0.5 */
+  static void
+  split_cubic( FT_26D6_Vec*  base )
+  {
+    FT_26D6  a, b, c;
+
+
+    base[6].x = base[3].x;
+    a = base[0].x + base[1].x;
+    b = base[1].x + base[2].x;
+    c = base[2].x + base[3].x;
+    base[5].x = c / 2;
+    c += b;
+    base[4].x = c / 4;
+    base[1].x = a / 2;
+    a += b;
+    base[2].x = a / 4;
+    base[3].x = ( a + c ) / 8;
+
+    base[6].y = base[3].y;
+    a = base[0].y + base[1].y;
+    b = base[1].y + base[2].y;
+    c = base[2].y + base[3].y;
+    base[5].y = c / 2;
+    c += b;
+    base[4].y = c / 4;
+    base[1].y = a / 2;
+    a += b;
+    base[2].y = a / 4;
+    base[3].y = ( a + c ) / 8;
+  }
+
+  /* the function splits a conic bezier curve     */
+  /* into a number of lines and adds them to      */
+  /* a list `out'. The function uses recursion    */
+  /* that is why a `max_splits' param is required */
+  /* for stopping.                                */
+  static FT_Error
+  split_sdf_conic( FT_Memory     memory,
+                   FT_26D6_Vec*  control_points,
+                   FT_Int        max_splits,
+                   SDF_Edge**    out )
+  {
+    FT_Error     error = FT_Err_Ok;
+    FT_26D6_Vec  cpos[5];
+    SDF_Edge*    left,*  right;
+
+
+    if ( !memory || !out  )
+    {
+      error = FT_THROW( Invalid_Argument );
+      goto Exit;
+    }
+
+    /* split the conic */
+    cpos[0] = control_points[0];
+    cpos[1] = control_points[1];
+    cpos[2] = control_points[2];
+
+    split_conic( cpos );
+
+    /* If max number of splits is done */
+    /* then stop and add the lines to  */
+    /* the list.                       */
+    if ( max_splits <= 2 )
+      goto Append;
+
+    /* If not max splits then keep splitting */
+    FT_CALL( split_sdf_conic( memory, &cpos[0], max_splits / 2, out ) );
+    FT_CALL( split_sdf_conic( memory, &cpos[2], max_splits / 2, out ) );
+
+    /* [NOTE]: This is not an efficient way of   */
+    /* splitting the curve. Check the deviation  */
+    /* instead and stop if the deviation is less */
+    /* than a pixel.                             */
+
+    goto Exit;
+
+  Append:
+
+    /* Allocation and add the lines to the list. */
+
+    FT_CALL( sdf_edge_new( memory, &left) );
+    FT_CALL( sdf_edge_new( memory, &right) );
+
+    left->start_pos  = cpos[0];
+    left->end_pos    = cpos[2];
+    left->edge_type  = SDF_EDGE_LINE;
+
+    right->start_pos = cpos[2];
+    right->end_pos   = cpos[4];
+    right->edge_type = SDF_EDGE_LINE;
+
+    left->next = right;
+    right->next = (*out);
+    *out = left;
+
+  Exit:
+    return error;
+  }
+
+  /* the function splits a cubic bezier curve     */
+  /* into a number of lines and adds them to      */
+  /* a list `out'. The function uses recursion    */
+  /* that is why a `max_splits' param is required */
+  /* for stopping.                                */
+  static FT_Error
+  split_sdf_cubic( FT_Memory     memory,
+                   FT_26D6_Vec*  control_points,
+                   FT_Int        max_splits,
+                   SDF_Edge**    out )
+  {
+    FT_Error     error = FT_Err_Ok;
+    FT_26D6_Vec  cpos[7];
+    SDF_Edge*    left,*  right;
+
+
+    if ( !memory || !out  )
+    {
+      error = FT_THROW( Invalid_Argument );
+      goto Exit;
+    }
+
+    /* split the conic */
+    cpos[0] = control_points[0];
+    cpos[1] = control_points[1];
+    cpos[2] = control_points[2];
+    cpos[3] = control_points[3];
+
+    split_cubic( cpos );
+
+    /* If max number of splits is done */
+    /* then stop and add the lines to  */
+    /* the list.                       */
+    if ( max_splits <= 2 )
+      goto Append;
+
+    /* If not max splits then keep splitting */
+    FT_CALL( split_sdf_cubic( memory, &cpos[0], max_splits / 2, out ) );
+    FT_CALL( split_sdf_cubic( memory, &cpos[3], max_splits / 2, out ) );
+
+    /* [NOTE]: This is not an efficient way of   */
+    /* splitting the curve. Check the deviation  */
+    /* instead and stop if the deviation is less */
+    /* than a pixel.                             */
+
+    goto Exit;
+
+  Append:
+
+    /* Allocation and add the lines to the list. */
+
+    FT_CALL( sdf_edge_new( memory, &left) );
+    FT_CALL( sdf_edge_new( memory, &right) );
+
+    left->start_pos  = cpos[0];
+    left->end_pos    = cpos[3];
+    left->edge_type  = SDF_EDGE_LINE;
+
+    right->start_pos = cpos[3];
+    right->end_pos   = cpos[6];
+    right->edge_type = SDF_EDGE_LINE;
+
+    left->next = right;
+    right->next = (*out);
+    *out = left;
+
+  Exit:
+    return error;
+  }
+
+  /* This function subdivide and entire shape   */
+  /* into line segment such that it doesn't     */
+  /* look visually different from the original  */
+  /* curve.                                     */
+  static FT_Error
+  split_sdf_shape( SDF_Shape*  shape )
+  {
+    FT_Error      error = FT_Err_Ok;
+    FT_Memory     memory;
+
+    SDF_Contour*  contours;
+    SDF_Contour*  new_contours = NULL;
+
+
+
+    if ( !shape || !shape->memory )
+    {
+      error = FT_THROW( Invalid_Argument );
+      goto Exit;
+    }
+
+    contours = shape->contours;
+    memory = shape->memory;
+
+    /* for each contour */
+    while ( contours )
+    {
+      SDF_Edge*     edges = contours->edges;
+      SDF_Edge*     new_edges = NULL;
+
+      SDF_Contour*  tempc;
+
+      /* for each edge */
+      while ( edges )
+      {
+        SDF_Edge*    edge = edges;
+        SDF_Edge*    temp;
+
+        switch ( edge->edge_type )
+        {
+        case SDF_EDGE_LINE:
+        {
+          /* Just create a duplicate edge in case    */
+          /* it is a line. We can use the same edge. */
+          FT_CALL( sdf_edge_new( memory, &temp ) );
+
+          ft_memcpy( temp, edge, sizeof( *edge ) );
+
+          temp->next = new_edges;
+          new_edges = temp;
+          break;
+        }
+        case SDF_EDGE_CONIC:
+        {
+          /* Subdivide the curve and add to the list. */
+          FT_26D6_Vec  ctrls[3];
+
+
+          ctrls[0] = edge->start_pos;
+          ctrls[1] = edge->control_a;
+          ctrls[2] = edge->end_pos;
+          error = split_sdf_conic( memory, ctrls, 32, &new_edges );
+          break;
+        }
+        case SDF_EDGE_CUBIC:
+        {
+          /* Subdivide the curve and add to the list. */
+          FT_26D6_Vec  ctrls[4];
+
+
+          ctrls[0] = edge->start_pos;
+          ctrls[1] = edge->control_a;
+          ctrls[2] = edge->control_b;
+          ctrls[3] = edge->end_pos;
+          error = split_sdf_cubic( memory, ctrls, 32, &new_edges );
+          break;
+        }
+        default:
+          error = FT_THROW( Invalid_Argument );
+          goto Exit;
+        }
+
+        edges = edges->next;
+      }
+
+      /* add to the contours list */
+      FT_CALL( sdf_contour_new( memory, &tempc ) );
+      tempc->next   = new_contours;
+      tempc->edges  = new_edges;
+      new_contours  = tempc;
+      new_edges     = NULL;
+
+      /* deallocate the contour */
+      tempc = contours;
+      contours = contours->next;
+
+      sdf_contour_done( memory, &tempc );
+    }
+
+    shape->contours = new_contours;
+
+  Exit:
+    return error;
+  }
+
 /* END */