ftgrays.c

一个Xpdf应用的例子

/***************************************************************************/
/*                                                                         */
/*  ftgrays.c                                                              */
/*                                                                         */
/*    A new `perfect' anti-aliasing renderer (body).                       */
/*                                                                         */
/*  Copyright 2000-2001 by                                                 */
/*  David Turner, Robert Wilhelm, and Werner Lemberg.                      */
/*                                                                         */
/*  This file is part of the FreeType project, and may only be used,       */
/*  modified, and distributed under the terms of the FreeType project      */
/*  license, LICENSE.TXT.  By continuing to use, modify, or distribute     */
/*  this file you indicate that you have read the license and              */
/*  understand and accept it fully.                                        */
/*                                                                         */
/***************************************************************************/

  /*************************************************************************/
  /*                                                                       */
  /*  This file can be compiled without the rest of the FreeType engine,   */
  /*  by defining the _STANDALONE_ macro when compiling it.  You also need */
  /*  to put the files `ftgrays.h' and `ftimage.h' into the current        */
  /*  compilation directory.  Typically, you could do something like       */
  /*                                                                       */
  /*  - copy `src/base/ftgrays.c' to your current directory                */
  /*                                                                       */
  /*  - copy `include/freetype/ftimage.h' and                              */
  /*    `include/freetype/ftgrays.h' to the same directory                 */
  /*                                                                       */
  /*  - compile `ftgrays' with the _STANDALONE_ macro defined, as in       */
  /*                                                                       */
  /*      cc -c -D_STANDALONE_ ftgrays.c                                   */
  /*                                                                       */
  /*  The renderer can be initialized with a call to                       */
  /*  `ft_gray_raster.gray_raster_new'; an anti-aliased bitmap can be      */
  /*  generated with a call to `ft_gray_raster.gray_raster_render'.        */
  /*                                                                       */
  /*  See the comments and documentation in the file `ftimage.h' for       */
  /*  more details on how the raster works.                                */
  /*                                                                       */
  /*************************************************************************/

  /*************************************************************************/
  /*                                                                       */
  /*  This is a new anti-aliasing scan-converter for FreeType 2.  The      */
  /*  algorithm used here is _very_ different from the one in the standard */
  /*  `ftraster' module.  Actually, `ftgrays' computes the _exact_         */
  /*  coverage of the outline on each pixel cell.                          */
  /*                                                                       */
  /*  It is based on ideas that I initially found in Raph Levien's         */
  /*  excellent LibArt graphics library (see http://www.levien.com/libart  */
  /*  for more information, though the web pages do not tell anything      */
  /*  about the renderer; you'll have to dive into the source code to      */
  /*  understand how it works).                                            */
  /*                                                                       */
  /*  Note, however, that this is a _very_ different implementation        */
  /*  compared to Raph's.  Coverage information is stored in a very        */
  /*  different way, and I don't use sorted vector paths.  Also, it        */
  /*  doesn't use floating point values.                                   */
  /*                                                                       */
  /*  This renderer has the following advantages:                          */
  /*                                                                       */
  /*  - It doesn't need an intermediate bitmap.  Instead, one can supply   */
  /*    a callback function that will be called by the renderer to draw    */
  /*    gray spans on any target surface.  You can thus do direct          */
  /*    composition on any kind of bitmap, provided that you give the      */
  /*    renderer the right callback.                                       */
  /*                                                                       */
  /*  - A perfect anti-aliaser, i.e., it computes the _exact_ coverage on  */
  /*    each pixel cell                                                    */
  /*                                                                       */
  /*  - It performs a single pass on the outline (the `standard' FT2       */
  /*    renderer makes two passes).                                        */
  /*                                                                       */
  /*  - It can easily be modified to render to _any_ number of gray levels */
  /*    cheaply.                                                           */
  /*                                                                       */
  /*  - For small (< 20) pixel sizes, it is faster than the standard       */
  /*    renderer.                                                          */
  /*                                                                       */
  /*************************************************************************/


#include <string.h>             /* for memcpy() */
#include <setjmp.h>


/* experimental support for gamma correction within the rasterizer */
#define xxxGRAYS_USE_GAMMA


  /*************************************************************************/
  /*                                                                       */
  /* 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  trace_aaraster


#define ErrRaster_MemoryOverflow   -4

#ifdef _STANDALONE_


#define ErrRaster_Invalid_Mode     -2
#define ErrRaster_Invalid_Outline  -1

#include "ftimage.h"
#include "ftgrays.h"

  /* This macro is used to indicate that a function parameter is unused. */
  /* Its purpose is simply to reduce compiler warnings.  Note also that  */
  /* simply defining it as `(void)x' doesn't avoid warnings with certain */
  /* ANSI compilers (e.g. LCC).                                          */
#define FT_UNUSED( x )  (x) = (x)

  /* Disable the tracing mechanism for simplicity -- developers can      */
  /* activate it easily by redefining these two macros.                  */
#ifndef FT_ERROR
#define FT_ERROR( x )  do ; while ( 0 )     /* nothing */
#endif

#ifndef FT_TRACE
#define FT_TRACE( x )  do ; while ( 0 )     /* nothing */
#endif


#else /* _STANDALONE_ */


#include <ft2build.h>
#include "ftgrays.h"
#include FT_INTERNAL_OBJECTS_H
#include FT_INTERNAL_DEBUG_H
#include FT_OUTLINE_H

#include "ftsmerrs.h"

#define ErrRaster_Invalid_Mode     Smooth_Err_Cannot_Render_Glyph
#define ErrRaster_Invalid_Outline  Smooth_Err_Invalid_Outline


#endif /* _STANDALONE_ */


#ifndef MEM_Set
#define  MEM_Set( d, s, c )  memset( d, s, c )
#endif

  /* define this to dump debugging information */
#define xxxDEBUG_GRAYS

  /* as usual, for the speed hungry :-) */

#ifndef FT_STATIC_RASTER


#define RAS_ARG   PRaster  raster
#define RAS_ARG_  PRaster  raster,

#define RAS_VAR   raster
#define RAS_VAR_  raster,

#define ras       (*raster)


#else /* FT_STATIC_RASTER */


#define RAS_ARG   /* empty */
#define RAS_ARG_  /* empty */
#define RAS_VAR   /* empty */
#define RAS_VAR_  /* empty */

  static TRaster  ras;


#endif /* FT_STATIC_RASTER */


  /* must be at least 6 bits! */
#define PIXEL_BITS  8

#define ONE_PIXEL       ( 1L << PIXEL_BITS )
#define PIXEL_MASK      ( -1L << PIXEL_BITS )
#define TRUNC( x )      ( (x) >> PIXEL_BITS )
#define SUBPIXELS( x )  ( (x) << PIXEL_BITS )
#define FLOOR( x )      ( (x) & -ONE_PIXEL )
#define CEILING( x )    ( ( (x) + ONE_PIXEL - 1 ) & -ONE_PIXEL )
#define ROUND( x )      ( ( (x) + ONE_PIXEL / 2 ) & -ONE_PIXEL )

#if PIXEL_BITS >= 6
#define UPSCALE( x )    ( (x) << ( PIXEL_BITS - 6 ) )
#define DOWNSCALE( x )  ( (x) >> ( PIXEL_BITS - 6 ) )
#else
#define UPSCALE( x )    ( (x) >> ( 6 - PIXEL_BITS ) )
#define DOWNSCALE( x )  ( (x) << ( 6 - PIXEL_BITS ) )
#endif

  /* Define this if you want to use a more compact storage scheme.  This   */
  /* increases the number of cells available in the render pool but slows  */
  /* down the rendering a bit.  It is useful if you have a really tiny     */
  /* render pool.                                                          */
#define xxxGRAYS_COMPACT


  /*************************************************************************/
  /*                                                                       */
  /*   TYPE DEFINITIONS                                                    */
  /*                                                                       */

  /* don't change the following types to FT_Int or FT_Pos, since we might */
  /* need to define them to "float" or "double" when experimenting with   */
  /* new algorithms                                                       */

  typedef int   TScan;   /* integer scanline/pixel coordinate */
  typedef long  TPos;    /* sub-pixel coordinate              */

  /* determine the type used to store cell areas.  This normally takes at */
  /* least PIXEL_BYTES*2 + 1.  On 16-bit systems, we need to use `long'   */
  /* instead of `int', otherwise bad things happen                        */

#if PIXEL_BITS <= 7

  typedef int   TArea;

#else /* PIXEL_BITS >= 8 */

  /* approximately determine the size of integers using an ANSI-C header */
#include <limits.h>

#if UINT_MAX == 0xFFFFU
  typedef long  TArea;
#else
  typedef int  TArea;
#endif

#endif /* PIXEL_BITS >= 8 */


  /* maximal number of gray spans in a call to the span callback */
#define FT_MAX_GRAY_SPANS  32


#ifdef GRAYS_COMPACT

  typedef struct  TCell_
  {
    short  x     : 14;
    short  y     : 14;
    int    cover : PIXEL_BITS + 2;
    int    area  : PIXEL_BITS * 2 + 2;

  } TCell, *PCell;

#else /* GRAYS_COMPACT */

  typedef struct  TCell_
  {
    TScan  x;
    TScan  y;
    int    cover;
    TArea  area;

  } TCell, *PCell;

#endif /* GRAYS_COMPACT */


  typedef struct  TRaster_
  {
    PCell  cells;
    int    max_cells;
    int    num_cells;

    TScan  min_ex, max_ex;
    TScan  min_ey, max_ey;

    TArea  area;
    int    cover;
    int    invalid;

    TScan  ex, ey;
    TScan  cx, cy;
    TPos   x,  y;

    TScan  last_ey;

    FT_Vector   bez_stack[32 * 3 + 1];
    int         lev_stack[32];

    FT_Outline  outline;
    FT_Bitmap   target;
    FT_BBox     clip_box;

    FT_Span     gray_spans[FT_MAX_GRAY_SPANS];
    int         num_gray_spans;

    FT_Raster_Span_Func  render_span;
    void*                render_span_data;
    int                  span_y;

    int  band_size;
    int  band_shoot;
    int  conic_level;
    int  cubic_level;

    void*    memory;
    jmp_buf  jump_buffer;

#ifdef GRAYS_USE_GAMMA
    FT_Byte  gamma[257];
#endif

  } TRaster, *PRaster;


  /*************************************************************************/
  /*                                                                       */
  /* Initialize the cells table.                                           */
  /*                                                                       */
  static void
  gray_init_cells( RAS_ARG_ void*  buffer,
                   long            byte_size )
  {
    ras.cells     = (PCell)buffer;
    ras.max_cells = byte_size / sizeof ( TCell );
    ras.num_cells = 0;
    ras.area      = 0;
    ras.cover     = 0;
    ras.invalid   = 1;
  }


  /*************************************************************************/
  /*                                                                       */
  /* Compute the outline bounding box.                                     */
  /*                                                                       */
  static void
  gray_compute_cbox( RAS_ARG )
  {
    FT_Outline*  outline = &ras.outline;
    FT_Vector*   vec     = outline->points;
    FT_Vector*   limit   = vec + outline->n_points;


    if ( outline->n_points <= 0 )
    {
      ras.min_ex = ras.max_ex = 0;
      ras.min_ey = ras.max_ey = 0;
      return;
    }

    ras.min_ex = ras.max_ex = vec->x;
    ras.min_ey = ras.max_ey = vec->y;

    vec++;

    for ( ; vec < limit; vec++ )
    {
      TPos  x = vec->x;
      TPos  y = vec->y;


      if ( x < ras.min_ex ) ras.min_ex = x;
      if ( x > ras.max_ex ) ras.max_ex = x;
      if ( y < ras.min_ey ) ras.min_ey = y;
      if ( y > ras.max_ey ) ras.max_ey = y;
    }

    /* truncate the bounding box to integer pixels */
    ras.min_ex = ras.min_ex >> 6;
    ras.min_ey = ras.min_ey >> 6;
    ras.max_ex = ( ras.max_ex + 63 ) >> 6;
    ras.max_ey = ( ras.max_ey + 63 ) >> 6;
  }


  /*************************************************************************/
  /*                                                                       */
  /* Record the current cell in the table.                                 */
  /*                                                                       */
  static void
  gray_record_cell( RAS_ARG )
  {
    PCell  cell;


    if ( !ras.invalid && ( ras.area | ras.cover ) )
    {
      if ( ras.num_cells >= ras.max_cells )
        longjmp( ras.jump_buffer, 1 );

      cell        = ras.cells + ras.num_cells++;
      cell->x     = ras.ex - ras.min_ex;
      cell->y     = ras.ey - ras.min_ey;
      cell->area  = ras.area;
      cell->cover = ras.cover;
    }
  }


  /*************************************************************************/
  /*                                                                       */
  /* Set the current cell to a new position.                               */
  /*                                                                       */
  static void
  gray_set_cell( RAS_ARG_ TScan  ex,
                          TScan  ey )
  {
    int  invalid, record, clean;


    /* Move the cell pointer to a new position.  We set the `invalid'      */
    /* flag to indicate that the cell isn't part of those we're interested */
    /* in during the render phase.  This means that:                       */
    /*                                                                     */
    /* . the new vertical position must be within min_ey..max_ey-1.        */
    /* . the new horizontal position must be strictly less than max_ex     */
    /*                                                                     */
    /* Note that if a cell is to the left of the clipping region, it is    */
    /* actually set to the (min_ex-1) horizontal position.                 */

    record  = 0;
    clean   = 1;

    invalid = ( ey < ras.min_ey || ey >= ras.max_ey || ex >= ras.max_ex );
    if ( !invalid )
    {
      /* All cells that are on the left of the clipping region go to the */
      /* min_ex - 1 horizontal position.                                 */
      if ( ex < ras.min_ex )
        ex = ras.min_ex - 1;

      /* if our position is new, then record the previous cell */
      if ( ex != ras.ex || ey != ras.ey )
        record = 1;
      else
        clean = ras.invalid;  /* do not clean if we didn't move from */
                              /* a valid cell                        */
    }

    /* record the previous cell if needed (i.e., if we changed the cell */
    /* position, of changed the `invalid' flag)                         */
    if ( ras.invalid != invalid || record )
      gray_record_cell( RAS_VAR );

    if ( clean )
    {
      ras.area  = 0;
      ras.cover = 0;
    }

    ras.invalid = invalid;
    ras.ex      = ex;
    ras.ey      = ey;
  }


  /*************************************************************************/
  /*                                                                       */
  /* Start a new contour at a given cell.                                  */
  /*                                                                       */
  static void
  gray_start_cell( RAS_ARG_  TScan  ex,
                             TScan  ey )
  {
    if ( ex < ras.min_ex )
      ex = ras.min_ex - 1;

    ras.area    = 0;
    ras.cover   = 0;
    ras.ex      = ex;
    ras.ey      = ey;
    ras.last_ey = SUBPIXELS( ey );
    ras.invalid = 0;

    gray_set_cell( RAS_VAR_ ex, ey );
  }


  /*************************************************************************/
  /*                                                                       */
  /* Render a scanline as one or more cells.                               */
  /*                                                                       */
  static void
  gray_render_scanline( RAS_ARG_  TScan  ey,
                                  TPos   x1,
                                  TScan  y1,
                                  TPos   x2,
                                  TScan  y2 )
  {
    TScan  ex1, ex2, fx1, fx2, delta;
    long   p, first, dx;
    int    incr, lift, mod, rem;


    dx = x2 - x1;

    ex1 = TRUNC( x1 ); /* if (ex1 >= ras.max_ex) ex1 = ras.max_ex-1; */
    ex2 = TRUNC( x2 ); /* if (ex2 >= ras.max_ex) ex2 = ras.max_ex-1; */
    fx1 = x1 - SUBPIXELS( ex1 );
    fx2 = x2 - SUBPIXELS( ex2 );

    /* trivial case.  Happens often */
    if ( y1 == y2 )
    {
      gray_set_cell( RAS_VAR_ ex2, ey );
      return;
    }

    /* everything is located in a single cell.  That is easy! */
    /*                                                        */
    if ( ex1 == ex2 )
    {
      delta      = y2 - y1;
      ras.area  += (TArea)( fx1 + fx2 ) * delta;
      ras.cover += delta;
      return;
    }

    /* ok, we'll have to render a run of adjacent cells on the same */
    /* scanline...                                                  */
    /*                                                              */
    p     = ( ONE_PIXEL - fx1 ) * ( y2 - y1 );
    first = ONE_PIXEL;
    incr  = 1;

    if ( dx < 0 )
    {
      p     = fx1 * ( y2 - y1 );
      first = 0;
      incr  = -1;
      dx    = -dx;