[sdf] Added common elements for `sdf' and `bsdf' renderers.

* src/sdf/ftsdfrend.c (*): Added common renderer struct and
  declaration of both the renderers.

* src/sdf/ftsdfcommon.h (*): Added common properties, typedefs,
  macros etc.

* src/sdf/ftsdferrs.h (*): Error definitions for the module.

3 files changed, 227 insertions, 0 deletions

diff --git a/src/sdf/ftsdfcommon.h b/src/sdf/ftsdfcommon.h
index b8284ac68..b069077cb 100644
--- a/src/sdf/ftsdfcommon.h
+++ b/src/sdf/ftsdfcommon.h
@@ -1,7 +1,136 @@
 
+  /****************************************************
+   *
+   * This file contain common function and properties
+   * for both `sdf' and `bsdf' renderer.
+   *
+   */
+
 #ifndef FTSDFCOMMON_H_
 #define FTSDFCOMMON_H_
 
+#include <ft2build.h>
+#include FT_CONFIG_CONFIG_H
+#include <freetype/freetype.h>
+
+FT_BEGIN_HEADER
+
+  /**************************************************************************
+   *
+   * default values (cannot be set individually for each renderer)
+   *
+   */
+
+  /* default spread value */
+  #define DEFAULT_SPREAD  8
+
+  /* minimum spread supported by the renderer. */
+  #define MIN_SPREAD      2
+
+  /* maximum spread supported by the renderer. */
+  #define MAX_SPREAD      32
+
+  /**************************************************************************
+   *
+   * common definitions (cannot be set individually for each renderer)
+   *
+   */
+
+  /* If it is defined to 1 then the rasterizer will use squared distances */
+  /* for computation. It can greatly improve the performance but there is */
+  /* a chance of overflow and artifacts. You can safely use it upto a     */
+  /* pixel size of 128.                                                   */
+  #ifndef USE_SQUARED_DISTANCES
+  #  define USE_SQUARED_DISTANCES 0
+  #endif
+
+  /**************************************************************************
+   *
+   * common macros
+   *
+   */
+
+  /* convert int to 26.6 fixed point   */
+  #define FT_INT_26D6( x )   ( x * 64 )
+
+  /* convert int to 16.16 fixed point  */
+  #define FT_INT_16D16( x )  ( x * 65536 )
+
+  /* convert 26.6 to 16.16 fixed point */
+  #define FT_26D6_16D16( x ) ( x * 1024 )
+
+  /* Convenient macro which calls the function */
+  /* and returns if any error occurs.          */
+  #define FT_CALL( x ) do                          \
+                       {                           \
+                         error = ( x );            \
+                         if ( error != FT_Err_Ok ) \
+                           goto Exit;              \
+                       } while ( 0 )
+
+  /* [IMPORTANT]: The macro `VECTOR_LENGTH_16D16' is not always the same */
+  /* and must not be used anywhere except a few places. This macro is    */
+  /* controlled by the `USE_SQUARED_DISTANCES' macro. It compute squared */
+  /* distance or actual distance based on `USE_SQUARED_DISTANCES' value. */
+  /* By using squared distances the performance can be greatly improved  */
+  /* but there is a risk of overflow. Use it wisely.                     */
+  #if USE_SQUARED_DISTANCES
+  #  define VECTOR_LENGTH_16D16( v ) ( FT_MulFix( v.x, v.x ) + \
+                                       FT_MulFix( v.y, v.y ) )
+  #else
+  #  define VECTOR_LENGTH_16D16( v ) FT_Vector_Length( &v )
+  #endif
+
+  /**************************************************************************
+   *
+   * common typedefs
+   *
+   */
+
+  typedef  FT_Vector FT_26D6_Vec;   /* with 26.6 fixed point components  */
+  typedef  FT_Vector FT_16D16_Vec;  /* with 16.16 fixed point components */
+
+  typedef  FT_Fixed  FT_16D16;      /* 16.16 fixed point representation  */
+  typedef  FT_Fixed  FT_26D6;       /* 26.6 fixed point representation   */
+  typedef  FT_Short  FT_6D10;       /* 6.10 fixed point representation   */
+
+  typedef  FT_BBox   FT_CBox;       /* control box of a curve            */
+
+  /**************************************************************************
+   *
+   * common functions
+   *
+   */
+
+  /* Original Algorithm: https://github.com/chmike/fpsqrt */
+  /* Use this to compute the square root of a 16.16 fixed */
+  /* point number.                                        */
+  static FT_16D16
+  square_root( FT_16D16  val )
+  {
+    FT_ULong t, q, b, r;
+
+
+    r = val;
+    b = 0x40000000;
+    q = 0;
+    while( b > 0x40 )
+    {
+      t = q + b;
+      if( r >= t )
+      {
+        r -= t;
+        q = t + b;
+      }
+      r <<= 1;
+      b >>= 1;
+    }
+    q >>= 8;
+
+    return q;
+  }
+
+FT_END_HEADER
 
 #endif /* FTSDFCOMMON_H_ */
 
diff --git a/src/sdf/ftsdferrs.h b/src/sdf/ftsdferrs.h
index d102e7fde..b9f412fe9 100644
--- a/src/sdf/ftsdferrs.h
+++ b/src/sdf/ftsdferrs.h
@@ -2,6 +2,15 @@
 #ifndef FTSDFERRS_H_
 #define FTSDFERRS_H_
 
+#include <freetype/ftmoderr.h>
+
+#undef FTERRORS_H_
+
+#undef  FT_ERR_PREFIX
+#define FT_ERR_PREFIX  Sdf_Err_
+#define FT_ERR_BASE    FT_Mod_Err_Sdf
+
+#include <freetype/fterrors.h>
 
 #endif /* FTSDFERRS_H_ */
 
diff --git a/src/sdf/ftsdfrend.h b/src/sdf/ftsdfrend.h
index 08cfa4ca2..4131a52f8 100644
--- a/src/sdf/ftsdfrend.h
+++ b/src/sdf/ftsdfrend.h
@@ -2,6 +2,95 @@
 #ifndef FTSDFREND_H_
 #define FTSDFREND_H_
 
+#include <freetype/ftrender.h>
+#include <freetype/ftmodapi.h>
+#include <freetype/internal/ftobjs.h>
+
+FT_BEGIN_HEADER
+
+
+  /**************************************************************************
+   *
+   * @struct:
+   *   SDF_Renderer_Module
+   *
+   * @description:
+   *   This struct extends the native renderer struct `FT_RendererRec'.
+   *   It is basically used to store various parameters required by the
+   *   renderer and some additional parameters which can be used to
+   *   tweak the output of the renderer.
+   *
+   * @fields:
+   *   root ::
+   *     The native rendere struct.
+   *
+   *   spread ::
+   *     This is an essential parameter/property required by the
+   *     rendere. `spread' defines the maximum unsigned value that
+   *     will be present in the final SDF output. For default value
+   *     check `ftsdfcommon.h'.
+   *
+   *   flip_sign ::
+   *     By default the position values are inside the contours i.e.
+   *     filled by a contour. If this property is true then that output
+   *     will be opposite from the default i.e. negative will be filled
+   *     by a contour.
+   *
+   *   flip_y ::
+   *     Setting this parameter to true makes the output image flipped
+   *     along the y-axis.
+   *   
+   *   overlaps ::
+   *     Set this to true to generate SDF for glyphs having overlapping
+   *     contours. The overlapping support is limited to glyph which do
+   *     not have self intersecting contours. Also, removing overlaps
+   *     require a considerable amount of extra memory and this is not
+   *     valid while generating SDF from bitmap.
+   *
+   * @note:
+   *   All properties except `overlaps' is valid for both `sdf' and
+   *   `bsdf' renderer.
+   */
+  typedef struct  SDF_Renderer_Module_
+  {
+    FT_RendererRec  root;
+    FT_UInt         spread;
+    FT_Bool         flip_sign;
+    FT_Bool         flip_y;
+    FT_Bool         overlaps;
+
+  } SDF_Renderer_Module, *SDF_Renderer;
+
+
+  /**************************************************************************
+   *
+   * @renderer:
+   *   ft_sdf_renderer_class
+   *
+   * @description:
+   *   Renderer to convert `FT_Outline' to signed distance fields.
+   *
+   */
+  FT_DECLARE_RENDERER( ft_sdf_renderer_class )
+
+
+  /**************************************************************************
+   *
+   * @renderer:
+   *   ft_bitmap_sdf_renderer_class
+   *
+   * @description:
+   *   This is not exactly a renderer, it's just a converter which
+   *   convert bitmaps to signed distance fields.
+   *
+   * @note:
+   *   This is not a separate module, it is a part of the `sdf' module.
+   *
+   */
+  FT_DECLARE_RENDERER( ft_bitmap_sdf_renderer_class )
+
+
+FT_END_HEADER
 
 #endif /* FTSDFREND_H_ */