[sdf -> bsdf] Added a basic overview of the `bsdf' rasterizer.

* src/sdf/ftbsdf.c: Added the citation of the original paper
  and added a overview of the process for generating SDF
  from bitmaps.

CMakeLists.txt

@@ -347,6 +347,7 @@ set(BASE_SRCS
   src/pshinter/pshinter.c
   src/psnames/psnames.c
   src/raster/raster.c
+  src/sdf/sdf.c
   src/sfnt/sfnt.c
   src/smooth/smooth.c
   src/truetype/truetype.c

include/freetype/config/ftmodule.h

@@ -26,5 +26,7 @@ FT_USE_MODULE( FT_Renderer_Class, ft_raster1_renderer_class )
 FT_USE_MODULE( FT_Module_Class, sfnt_module_class )
 FT_USE_MODULE( FT_Renderer_Class, ft_smooth_renderer_class )
 FT_USE_MODULE( FT_Driver_ClassRec, bdf_driver_class )
+FT_USE_MODULE( FT_Renderer_Class, ft_sdf_renderer_class )
+FT_USE_MODULE( FT_Renderer_Class, ft_bitmap_sdf_renderer_class )
 
 /* EOF */

include/freetype/freetype.h

@@ -3208,10 +3208,14 @@ FT_BEGIN_HEADER
    *   in the @FT_GlyphSlotRec structure gives the format of the returned
    *   bitmap.
    *
-   *   All modes except @FT_RENDER_MODE_MONO use 256 levels of opacity,
-   *   indicating pixel coverage.  Use linear alpha blending and gamma
-   *   correction to correctly render non-monochrome glyph bitmaps onto a
-   *   surface; see @FT_Render_Glyph.
+   *   All modes except @FT_RENDER_MODE_MONO and @FT_RENDER_MODE_SDF use 
+   *   256 levels of opacity, indicating pixel coverage.  Use linear alpha 
+   *   blending and gamma correction to correctly render non-monochrome glyph
+   *   bitmaps onto a surface; see @FT_Render_Glyph.
+   *
+   *   The @FT_RENDER_MODE_SDF is s special render mode which uses as much 
+   *   65536 distance values, indicating the signed distance from the grid
+   *   position to the nearest outline.
    *
    * @values:
    *   FT_RENDER_MODE_NORMAL ::
@@ -3238,6 +3242,13 @@ FT_BEGIN_HEADER
    *     bitmaps that are 3~times the height of the original glyph outline in
    *     pixels and use the @FT_PIXEL_MODE_LCD_V mode.
    *
+   *   FT_RENDER_MODE_SDF ::
+   *     This mode corresponds to 16-bit signed distance fields bitmap.  Each
+   *     pixel in a SDF bitmap contains information about the nearest edge of
+   *     the glyph outline.  The distances are calculated from the center of
+   *     the pixel and are positive if they are filled by the outline (i.e.
+   *     inside the outline) and negative otherwise.
+   *
    * @note:
    *   The selected render mode only affects vector glyphs of a font.
    *   Embedded bitmaps often have a different pixel mode like
@@ -3251,6 +3262,7 @@ FT_BEGIN_HEADER
     FT_RENDER_MODE_MONO,
     FT_RENDER_MODE_LCD,
     FT_RENDER_MODE_LCD_V,
+    FT_RENDER_MODE_SDF,
 
     FT_RENDER_MODE_MAX
 

include/freetype/ftimage.h

@@ -157,6 +157,12 @@ FT_BEGIN_HEADER
    *     in font files according to the OpenType specification.  We haven't
    *     found a single font using this format, however.
    *
+   *   FT_PIXEL_MODE_GRAY16 ::
+   *     A 16-bit per pixel bitmap used to represent signed distances in a 
+   *     signed distance field bitmap.  This is currently only used while
+   *     rendering using @FT_RENDER_MODE_SDF.  Note that this is a 2.14
+   *     fixed-point fractional value.
+   *
    *   FT_PIXEL_MODE_LCD ::
    *     An 8-bit bitmap, representing RGB or BGR decimated glyph images used
    *     for display on LCD displays; the bitmap is three times wider than
@@ -184,6 +190,7 @@ FT_BEGIN_HEADER
     FT_PIXEL_MODE_GRAY,
     FT_PIXEL_MODE_GRAY2,
     FT_PIXEL_MODE_GRAY4,
+    FT_PIXEL_MODE_GRAY16,
     FT_PIXEL_MODE_LCD,
     FT_PIXEL_MODE_LCD_V,
     FT_PIXEL_MODE_BGRA,
@@ -962,11 +969,17 @@ FT_BEGIN_HEADER
    *     will be clipped to a box specified in the `clip_box` field of the
    *     @FT_Raster_Params structure.  Otherwise, the `clip_box` is
    *     effectively set to the bounding box and all spans are generated.
+   *
+   *   FT_RASTER_FLAG_SDF ::
+   *     This flag is set to indicate that a signed distance field glyph
+   *     image should be generated.  This is only used while rendering with
+   *     `FT_RENDER_MODE_SDF' render mode.
    */
 #define FT_RASTER_FLAG_DEFAULT  0x0
 #define FT_RASTER_FLAG_AA       0x1
 #define FT_RASTER_FLAG_DIRECT   0x2
 #define FT_RASTER_FLAG_CLIP     0x4
+#define FT_RASTER_FLAG_SDF      0x8
 
   /* these constants are deprecated; use the corresponding */
   /* `FT_RASTER_FLAG_XXX` values instead                   */

include/freetype/ftmoderr.h

@@ -171,6 +171,7 @@
   FT_MODERRDEF( Type42,   0x1400, "Type 42 module" )
   FT_MODERRDEF( Winfonts, 0x1500, "Windows FON/FNT module" )
   FT_MODERRDEF( GXvalid,  0x1600, "GX validation module" )
+  FT_MODERRDEF( Sdf,      0x1700, "signed distance field raster module" )
 
 
 #ifdef FT_MODERR_END_LIST

include/freetype/internal/fttrace.h

@@ -40,6 +40,7 @@ FT_TRACE_DEF( psprops )   /* PS driver properties    (ftpsprop.c) */
 FT_TRACE_DEF( raccess )   /* resource fork accessor  (ftrfork.c)  */
 FT_TRACE_DEF( raster )    /* monochrome rasterizer   (ftraster.c) */
 FT_TRACE_DEF( smooth )    /* anti-aliasing raster    (ftgrays.c)  */
+FT_TRACE_DEF( sdf )       /* signed distance raster  (ftsdf.c)	  */
 FT_TRACE_DEF( synth )     /* bold/slant synthesizer  (ftsynth.c)  */
 
   /* Cache sub-system */

modules.cfg

@@ -99,6 +99,8 @@ RASTER_MODULES += raster
 # Anti-aliasing rasterizer.
 RASTER_MODULES += smooth
 
+# Signed distance field rasterizer.
+RASTER_MODULES += sdf
 
 ####
 #### auxiliary modules

src/base/ftobjs.c

@@ -4393,8 +4393,7 @@
       render->glyph_format = clazz->glyph_format;
 
       /* allocate raster object if needed */
-      if ( clazz->glyph_format == FT_GLYPH_FORMAT_OUTLINE &&
-           clazz->raster_class->raster_new                )
+      if ( clazz->raster_class->raster_new )
       {
         error = clazz->raster_class->raster_new( memory, &render->raster );
         if ( error )
@@ -4441,8 +4440,7 @@
 
 
       /* release raster object, if any */
-      if ( render->clazz->glyph_format == FT_GLYPH_FORMAT_OUTLINE &&
-           render->raster                                         )
+      if ( render->raster )
         render->clazz->raster_class->raster_done( render->raster );
 
       /* remove from list */
@@ -4537,9 +4535,6 @@
 
     switch ( slot->format )
     {
-    case FT_GLYPH_FORMAT_BITMAP:   /* already a bitmap, don't do anything */
-      break;
-
     default:
       if ( slot->internal->load_flags & FT_LOAD_COLOR )
       {

src/sdf/ftsdf.h

@@ -0,0 +1,77 @@
+
+#ifndef FTSDF_H_
+#define FTSDF_H_
+
+#include <ft2build.h>
+#include FT_CONFIG_CONFIG_H
+#include <freetype/ftimage.h>
+
+/* common properties and function */
+#include "ftsdfcommon.h"
+
+FT_BEGIN_HEADER
+
+  /**************************************************************************
+   *
+   * @struct:
+   *   SDF_Raster_Params
+   *
+   * @description:
+   *   This struct must be used for the raster render function
+   *   `FT_Raster_Render_Func' instead of `FT_Raster_Params' because
+   *   the rasterizer require some addition information to render properly.
+   *   So, this struct is used to pass additional parameter to the
+   *   rasterizer.
+   *
+   * @fields:
+   *   root ::
+   *     The native raster params struct.
+   *
+   *   spread ::
+   *     This is and 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 maked 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:
+   *   It is valid for both `sdf' and `bsdf' renderer.
+   *
+   */
+  typedef struct  SDF_Raster_Params_
+  {
+    FT_Raster_Params  root;
+    FT_UInt           spread;
+    FT_Bool           flip_sign;
+    FT_Bool           flip_y;
+    FT_Bool           overlaps;
+
+  } SDF_Raster_Params;
+
+  /* rasterizer to convert outline to SDF */
+  FT_EXPORT_VAR( const FT_Raster_Funcs ) ft_sdf_raster;
+
+  /* rasterizer to convert bitmap to SDF */
+  FT_EXPORT_VAR( const FT_Raster_Funcs ) ft_bitmap_sdf_raster;
+
+FT_END_HEADER
+
+#endif /* FTSDF_H_ */
+
+/* END */

src/sdf/ftsdfcommon.h

@@ -0,0 +1,137 @@
+
+  /****************************************************
+   *
+   * 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_ */
+
+/* END */

src/sdf/ftsdferrs.h

@@ -0,0 +1,18 @@
+
+#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_ */
+
+
+/* END */

src/sdf/ftsdfrend.c

@@ -0,0 +1,542 @@
+
+#include <freetype/internal/ftdebug.h>
+#include <freetype/internal/ftobjs.h>
+#include <freetype/internal/services/svprop.h>
+#include <freetype/ftoutln.h>
+#include <freetype/ftbitmap.h>
+#include "ftsdfrend.h"
+#include "ftsdf.h"
+
+#include "ftsdferrs.h"
+
+  /**************************************************************************
+   *
+   * The macro FT_COMPONENT is used in trace mode.  It is an implicit
+   * parameter of the FT_TRACE() and FT_ERROR() macros, used to print/log
+   * messages during execution.
+   */
+  #undef  FT_COMPONENT
+  #define FT_COMPONENT  sdf
+
+  /**************************************************************************
+   *
+   * macros and default property values
+   *
+   */
+
+  #define SDF_RENDERER( rend ) ( (SDF_Renderer)rend )
+
+  /**************************************************************************
+   *
+   * for setting properties
+   *
+   */
+
+  /* property setter function */
+  static FT_Error
+  sdf_property_set( FT_Module    module,
+                    const char*  property_name,
+                    const void*  value,
+                    FT_Bool      value_is_string )
+  {
+    FT_Error      error  = FT_Err_Ok;
+    SDF_Renderer  render = SDF_RENDERER( FT_RENDERER( module ) );
+
+
+    FT_UNUSED( value_is_string );
+
+    if ( ft_strcmp( property_name, "spread" ) == 0 )
+    {
+      FT_Int  val = *(const FT_Int*)value;
+
+
+      if ( val > MAX_SPREAD || val < MIN_SPREAD )
+      {
+        FT_TRACE0(( "[sdf] sdf_property_set: "
+                    "the `spread' property can have a "
+                    "value within range [%d, %d] (value provided %d)\n",
+                    MIN_SPREAD, MAX_SPREAD, val ));
+        error = FT_THROW( Invalid_Argument );
+        goto Exit;
+      }
+      render->spread = (FT_UInt)val;
+      FT_TRACE7(( "[sdf] sdf_property_set: "
+                  "updated property `spread' to %d\n", val ));
+    }
+    else if ( ft_strcmp( property_name, "flip_sign" ) == 0 )
+    {
+      FT_Int  val = *(const FT_Int*)value;
+
+
+      render->flip_sign = val ? 1 : 0;
+      FT_TRACE7(( "[sdf] sdf_property_set: "
+                  "updated property `flip_sign' to %d\n", val ));
+    }
+    else if ( ft_strcmp( property_name, "flip_y" ) == 0 )
+    {
+      FT_Int  val = *(const FT_Int*)value;
+
+
+      render->flip_y = val ? 1 : 0;
+      FT_TRACE7(( "[sdf] sdf_property_set: "
+                  "updated property `flip_y' to %d\n", val ));
+    }
+    else if ( ft_strcmp( property_name, "overlaps" ) == 0 )
+    {
+      FT_Int  val = *(const FT_Int*)value;
+
+
+      render->overlaps = val;
+      FT_TRACE7(( "[sdf] sdf_property_set: "
+                  "updated property `overlaps' to %d\n", val ));
+    }
+    else
+    {
+      FT_TRACE0(( "[sdf] sdf_property_set: "
+                  "missing property `%s'\n", property_name ));
+      error = FT_THROW( Missing_Property );
+    }
+
+  Exit:
+    return error;
+  }
+
+  /* property getter function */
+  static FT_Error
+  sdf_property_get( FT_Module    module,
+                    const char*  property_name,
+                    void*        value )
+  {
+    FT_Error      error = FT_Err_Ok;
+    SDF_Renderer  render = SDF_RENDERER( FT_RENDERER( module ) );
+
+
+    if ( ft_strcmp( property_name, "spread" ) == 0 )
+    {
+      FT_Int*  val = (FT_Int*)value;
+
+
+      *val = render->spread;
+    }
+    else if ( ft_strcmp( property_name, "flip_sign" ) == 0 )
+    {
+      FT_Int*  val = (FT_Int*)value;
+
+
+      *val = render->flip_sign;
+    }
+    else if ( ft_strcmp( property_name, "flip_y" ) == 0 )
+    {
+      FT_Int*  val = (FT_Int*)value;
+
+
+      *val = render->flip_y;
+    }
+    else if ( ft_strcmp( property_name, "overlaps" ) == 0 )
+    {
+      FT_Int*  val = (FT_Int*)value;
+
+
+      *val = render->overlaps;
+    }
+    else
+    {
+      FT_TRACE0(( "[sdf] sdf_property_get: "
+                  "missing property `%s'\n", property_name ));
+      error = FT_THROW( Missing_Property );
+    }
+
+    return error;
+  }
+
+  FT_DEFINE_SERVICE_PROPERTIESREC(
+    sdf_service_properties,
+
+    (FT_Properties_SetFunc)sdf_property_set,        /* set_property */
+    (FT_Properties_GetFunc)sdf_property_get )       /* get_property */
+
+
+  FT_DEFINE_SERVICEDESCREC1(
+    sdf_services,
+
+    FT_SERVICE_ID_PROPERTIES, &sdf_service_properties )
+
+  static FT_Module_Interface
+  ft_sdf_requester( FT_Renderer  render,
+                    const char*  module_interface )
+  {
+    FT_UNUSED( render );
+
+    return ft_service_list_lookup( sdf_services, module_interface );
+  }
+
+  /**************************************************************************
+   *
+   * interface functions
+   *
+   */
+
+  static FT_Error
+  ft_sdf_init( FT_Renderer  render )
+  {
+    SDF_Renderer  sdf_render = SDF_RENDERER( render );
+
+
+    sdf_render->spread    = DEFAULT_SPREAD;
+    sdf_render->flip_sign = 0;
+    sdf_render->flip_y    = 0;
+    sdf_render->overlaps  = 0;
+
+    return FT_Err_Ok;
+  }
+
+  static FT_Error
+  ft_sdf_done( FT_Renderer  render )
+  {
+    FT_UNUSED( render );
+
+    return FT_Err_Ok;
+  }
+
+  /* generate signed distance field from a glyph's slot image */
+  static FT_Error
+  ft_sdf_render( FT_Renderer       module,
+                 FT_GlyphSlot      slot,
+                 FT_Render_Mode    mode,
+                 const FT_Vector*  origin )
+  {
+    FT_Error     error   = FT_Err_Ok;
+    FT_Outline*  outline = &slot->outline;
+    FT_Bitmap*   bitmap  = &slot->bitmap;
+    FT_Memory    memory  = NULL;
+    FT_Renderer  render  = NULL;
+    FT_Pos       x_shift = 0;
+    FT_Pos       y_shift = 0;
+
+    FT_Pos       x_pad   = 0;
+    FT_Pos       y_pad   = 0;
+
+    SDF_Raster_Params  params;
+    SDF_Renderer       sdf_module = SDF_RENDERER( module );
+
+
+    render = &sdf_module->root;
+    memory = render->root.memory;
+
+    /* check if slot format is correct before rendering */
+    if ( slot->format != render->glyph_format )
+    {
+      error = FT_THROW( Invalid_Glyph_Format );
+      goto Exit;
+    }
+
+    /* check if render mode is correct */
+    if ( mode != FT_RENDER_MODE_SDF )
+    {
+      FT_ERROR(( "[sdf] ft_sdf_render: "
+                 "sdf module only render when "
+                 "using `FT_RENDER_MODE_SDF'\n" ));
+      error = FT_THROW( Cannot_Render_Glyph );
+      goto Exit;
+    }
+
+    /* deallocate the previously allocated bitmap */
+    if ( slot->internal->flags & FT_GLYPH_OWN_BITMAP )
+    {
+      FT_FREE( bitmap->buffer );
+      slot->internal->flags &= ~FT_GLYPH_OWN_BITMAP;
+    }
+
+    /* preset the bitmap using the glyph's outline;         */
+    /* the sdf bitmap is similar to an antialiased bitmap   */
+    /* with a slightly bigger size and different pixel mode */
+    if ( ft_glyphslot_preset_bitmap( slot, FT_RENDER_MODE_NORMAL, origin ) )
+    {
+      error = FT_THROW( Raster_Overflow );
+      goto Exit;
+    }
+
+    if ( !bitmap->rows || !bitmap->pitch )
+      goto Exit;
+
+    /* the padding will simply be equal to the `spread' */
+    x_pad = sdf_module->spread;
+    y_pad = sdf_module->spread;
+
+    /* apply the padding, will be in all the directions */
+    bitmap->rows  += y_pad * 2;
+    bitmap->width += x_pad * 2;
+
+    /* ignore the pitch, pixel mode and set custom */
+    bitmap->pixel_mode = FT_PIXEL_MODE_GRAY16;
+    bitmap->pitch = bitmap->width * 2;
+    bitmap->num_grays = 65535;
+
+    /* allocate new buffer */
+    if ( FT_ALLOC_MULT( bitmap->buffer, bitmap->rows, bitmap->pitch ) )
+      goto Exit;
+
+    slot->internal->flags |= FT_GLYPH_OWN_BITMAP;
+
+    x_shift  = 64 * -( slot->bitmap_left - x_pad );
+    y_shift  = 64 * -( slot->bitmap_top + y_pad );
+    y_shift += 64 * (FT_Int)bitmap->rows;
+
+    if ( origin )
+    {
+      x_shift += origin->x;
+      y_shift += origin->y;
+    }
+
+    /* translate outline to render it into the bitmap */
+    if ( x_shift || y_shift )
+      FT_Outline_Translate( outline, x_shift, y_shift );
+
+    /* set up parameters */
+    params.root.target = bitmap;
+    params.root.source = outline;
+    params.root.flags  = FT_RASTER_FLAG_SDF;
+    params.spread      = sdf_module->spread;
+    params.flip_sign   = sdf_module->flip_sign;
+    params.flip_y      = sdf_module->flip_y;
+    params.overlaps    = sdf_module->overlaps;
+
+    /* render the outline */
+    error = render->raster_render( render->raster, (const FT_Raster_Params*)&params );
+
+  Exit:
+    if ( !error )
+    {
+      /* the glyph is successfully rendered to a bitmap */
+      slot->format = FT_GLYPH_FORMAT_BITMAP;
+    }
+    else if ( slot->internal->flags & FT_GLYPH_OWN_BITMAP )
+    {
+      FT_FREE( bitmap->buffer );
+      slot->internal->flags &= ~FT_GLYPH_OWN_BITMAP;
+    }
+
+    if ( x_shift || y_shift )
+      FT_Outline_Translate( outline, -x_shift, -y_shift );
+
+    return error;
+  }
+
+  /* transform the glyph using matrix and/or delta */
+  static FT_Error
+  ft_sdf_transform( FT_Renderer       render,
+                    FT_GlyphSlot      slot,
+                    const FT_Matrix*  matrix,
+                    const FT_Vector*  delta )
+  {
+    FT_Error  error = FT_Err_Ok;
+
+
+    if ( slot->format != render->glyph_format )
+    {
+      error = FT_THROW( Invalid_Argument );
+      goto Exit;
+    }
+
+    if ( matrix )
+      FT_Outline_Transform( &slot->outline, matrix );
+
+    if ( delta )
+      FT_Outline_Translate( &slot->outline, delta->x, delta->y );
+
+  Exit:
+    return error;
+  }
+
+  /* returns the control box of glyph's outline */
+  static void
+  ft_sdf_get_cbox( FT_Renderer   render,
+                   FT_GlyphSlot  slot,
+                   FT_BBox*      cbox )
+  {
+    FT_ZERO( cbox );
+
+    if ( slot->format == render->glyph_format )
+      FT_Outline_Get_CBox( &slot->outline, cbox );
+  }
+
+  /* set render specific modes or attributes */
+  static FT_Error
+  ft_sdf_set_mode( FT_Renderer  render,
+                   FT_ULong     mode_tag,
+                   FT_Pointer   data )
+  {
+    /* pass it to the rasterizer */
+    return render->clazz->raster_class->raster_set_mode( render->raster,
+                                                         mode_tag,
+                                                         data );
+  }
+
+  FT_DEFINE_RENDERER(
+    ft_sdf_renderer_class,
+
+    FT_MODULE_RENDERER,
+    sizeof( SDF_Renderer_Module ),
+
+    "sdf",
+    0x10000L,
+    0x20000L,
+
+    NULL,
+
+    (FT_Module_Constructor) ft_sdf_init,
+    (FT_Module_Destructor)  ft_sdf_done,
+    (FT_Module_Requester)   ft_sdf_requester,
+
+    FT_GLYPH_FORMAT_OUTLINE,
+
+    (FT_Renderer_RenderFunc)    ft_sdf_render,     /* render_glyph    */
+    (FT_Renderer_TransformFunc) ft_sdf_transform,  /* transform_glyph */
+    (FT_Renderer_GetCBoxFunc)   ft_sdf_get_cbox,   /* get_glyph_cbox  */
+    (FT_Renderer_SetModeFunc)   ft_sdf_set_mode,   /* set_mode        */
+
+    (FT_Raster_Funcs*)&ft_sdf_raster               /* raster_class    */
+  )
+
+  /*************************************************************************/
+  /*************************************************************************/
+  /**                                                                     **/
+  /**  BITMAP TO SDF CONVERTER                                            **/
+  /**                                                                     **/
+  /*************************************************************************/
+  /*************************************************************************/
+
+  /* generate signed distance field from glyph's bitmap */
+  static FT_Error
+  ft_bsdf_render( FT_Renderer       module,
+                  FT_GlyphSlot      slot,
+                  FT_Render_Mode    mode,
+                  const FT_Vector*  origin )
+  {
+    FT_Error     error   = FT_Err_Ok;
+    FT_Bitmap*   bitmap  = &slot->bitmap;
+    FT_Memory    memory  = NULL;
+    FT_Renderer  render  = NULL;
+    FT_Bitmap    target;
+
+    FT_Pos      x_pad    = 0;
+    FT_Pos      y_pad    = 0;
+
+    SDF_Raster_Params  params;
+    SDF_Renderer       sdf_module = SDF_RENDERER( module );
+
+
+    /* initialize the bitmap in case any error occurs */
+    FT_Bitmap_Init( &target );
+
+    render = &sdf_module->root;
+    memory = render->root.memory;
+
+    /* check if slot format is correct before rendering */
+    if ( slot->format != render->glyph_format )
+    {
+      FT_ERROR(( "[bsdf] ft_bsdf_render: "
+                 "bsdf renderer require the slot "
+                 "format to be a bitmap\n" ));
+      error = FT_THROW( Invalid_Glyph_Format );
+      goto Exit;
+    }
+
+    /* check if render mode is correct */
+    if ( mode != FT_RENDER_MODE_SDF )
+    {
+      FT_ERROR(( "[bsdf] ft_bsdf_render: "
+                 "sdf module only render when "
+                 "using `FT_RENDER_MODE_SDF'\n" ));
+      error = FT_THROW( Cannot_Render_Glyph );
+      goto Exit;
+    }
+
+    if ( origin )
+    {
+      FT_ERROR(( "[bsdf] ft_bsdf_render: "
+                 "bsdf renderer can't translate "
+                 "the bitmap\n" ));
+      error = FT_THROW( Unimplemented_Feature );
+      goto Exit;
+    }
+
+    if ( !bitmap->rows || !bitmap->pitch )
+      goto Exit;
+
+    FT_Bitmap_New( &target );
+
+    /* the padding will simply be equal to the `spread' */
+    x_pad = sdf_module->spread;
+    y_pad = sdf_module->spread;
+
+    /* apply the padding, will be in all the directions */
+    target.rows = bitmap->rows + y_pad * 2;
+    target.width = bitmap->width + x_pad * 2;
+
+    /* setup the target bitmap */
+    target.pixel_mode = FT_PIXEL_MODE_GRAY16;
+    target.pitch = target.width * 2;
+    target.num_grays = 65535;
+
+    if ( FT_ALLOC_MULT( target.buffer, target.rows, target.pitch ) )
+      goto Exit;
+
+    /* set up parameters */
+    params.root.target = &target;
+    params.root.source = bitmap;
+    params.root.flags  = FT_RASTER_FLAG_SDF;
+    params.spread      = sdf_module->spread;
+    params.flip_sign   = sdf_module->flip_sign;
+    params.flip_y      = sdf_module->flip_y;
+
+    error = render->raster_render( render->raster,
+                                   (const FT_Raster_Params*)&params );
+  Exit:
+    if ( !error )
+    {
+      /* the glyph is successfully converted to a SDF */
+      if ( slot->internal->flags & FT_GLYPH_OWN_BITMAP )
+      {
+        FT_FREE( bitmap->buffer );
+        slot->internal->flags &= ~FT_GLYPH_OWN_BITMAP;
+      }
+
+      slot->bitmap = target;
+      slot->internal->flags |= FT_GLYPH_OWN_BITMAP;
+    }
+    else if ( target.buffer )
+    {
+      FT_FREE( target.buffer );
+    }
+
+    return error;
+  }
+
+  FT_DEFINE_RENDERER(
+    ft_bitmap_sdf_renderer_class,
+
+    FT_MODULE_RENDERER,
+    sizeof( SDF_Renderer_Module ),
+
+    "bsdf",
+    0x10000L,
+    0x20000L,
+
+    NULL,
+
+    (FT_Module_Constructor) ft_sdf_init,
+    (FT_Module_Destructor)  ft_sdf_done,
+    (FT_Module_Requester)   ft_sdf_requester,
+
+    FT_GLYPH_FORMAT_BITMAP,
+
+    (FT_Renderer_RenderFunc)    ft_bsdf_render,    /* render_glyph    */
+    (FT_Renderer_TransformFunc) ft_sdf_transform,  /* transform_glyph */
+    (FT_Renderer_GetCBoxFunc)   ft_sdf_get_cbox,   /* get_glyph_cbox  */
+    (FT_Renderer_SetModeFunc)   ft_sdf_set_mode,   /* set_mode        */
+
+    (FT_Raster_Funcs*)&ft_bitmap_sdf_raster        /* raster_class    */
+  )
+
+/* END */

src/sdf/ftsdfrend.h

@@ -0,0 +1,100 @@
+
+#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 and 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 maked 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_ */
+
+
+/* END */

src/sdf/module.mk

@@ -0,0 +1,16 @@
+
+
+FTMODULE_H_COMMANDS += SDF_RENDERER
+FTMODULE_H_COMMANDS += BSDF_RENDERER
+
+define SDF_RENDERER
+$(OPEN_DRIVER) FT_Renderer_Class, ft_sdf_renderer_class $(CLOSE_DRIVER)
+$(ECHO_DRIVER)sdf       $(ECHO_DRIVER_DESC)signed distance field renderer$(ECHO_DRIVER_DONE)
+endef
+
+define BSDF_RENDERER
+$(OPEN_DRIVER) FT_Renderer_Class, ft_bitmap_sdf_renderer_class $(CLOSE_DRIVER)
+$(ECHO_DRIVER)bsdf      $(ECHO_DRIVER_DESC)bitmap to signed distance field converter$(ECHO_DRIVER_DONE)
+endef
+
+#EOF

src/sdf/rules.mk

@@ -0,0 +1,63 @@
+
+
+# sdf driver directory
+#
+SDF_DIR := $(SRC_DIR)/sdf
+
+
+# compilation flags for the driver
+#
+SDF_COMPILE := $(CC) $(ANSIFLAGS)                            \
+                     $I$(subst /,$(COMPILER_SEP),$(SDF_DIR)) \
+                     $(INCLUDE_FLAGS)                        \
+                     $(FT_CFLAGS)
+
+
+# sdf driver sources (i.e., C files)
+#
+SDF_DRV_SRC := $(SDF_DIR)/ftsdfrend.c  \
+               $(SDF_DIR)/ftsdf.c      \
+               $(SDF_DIR)/ftbsdf.c
+
+
+# sdf driver headers
+#
+SDF_DRV_H := $(SDF_DIR)/ftsdfrend.h  \
+             $(SDF_DIR)/ftsdf.h      \
+             $(SDF_DIR)/ftsdferrs.h  \
+             $(SDF_DIR)/ftsdfcommon.h
+
+
+# sdf driver object(s)
+#
+#   SDF_DRV_OBJ_M is used during `multi' builds.
+#   SDF_DRV_OBJ_S is used during `single' builds.
+#
+SDF_DRV_OBJ_M := $(SDF_DRV_SRC:$(SDF_DIR)/%.c=$(OBJ_DIR)/%.$O)
+SDF_DRV_OBJ_S := $(OBJ_DIR)/sdf.$O
+
+
+# sdf driver source file for single build
+#
+SDF_DRV_SRC_S := $(SDF_DIR)/sdf.c
+
+
+# sdf driver - single object
+#
+$(SDF_DRV_OBJ_S): $(SDF_DRV_SRC_S) $(SDF_DRV_SRC) \
+                  $(FREETYPE_H) $(SDF_DRV_H)
+	$(SDF_COMPILE) $T$(subst /,$(COMPILER_SEP),$@ $(SDF_DRV_SRC_S))
+
+
+# sdf driver - multiple objects
+#
+$(OBJ_DIR)/%.$O: $(SDF_DIR)/%.c $(FREETYPE_H) $(SDF_DRV_H)
+	$(SDF_COMPILE) $T$(subst /,$(COMPILER_SEP),$@ $<)
+
+
+# update main driver list
+#
+DRV_OBJS_S += $(SDF_DRV_OBJ_S)
+DRV_OBJS_M += $(SDF_DRV_OBJ_M)
+
+# EOF

src/sdf/sdf.c

@@ -0,0 +1,10 @@
+
+
+#define FT_MAKE_OPTION_SINGLE_OBJECT
+
+#include "ftsdfrend.c"
+#include "ftbsdf.c"
+#include "ftsdf.c"
+
+
+/* END */