afwarp.c

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/***************************************************************************/
/*                                                                         */
/*  afwarp.c                                                               */
/*                                                                         */
/*    Auto-fitter warping algorithm (body).                                */
/*                                                                         */
/*  Copyright 2006-2018 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.                                        */
/*                                                                         */
/***************************************************************************/
 
 
  /*
   *  The idea of the warping code is to slightly scale and shift a glyph
   *  within a single dimension so that as much of its segments are aligned
   *  (more or less) on the grid.  To find out the optimal scaling and
   *  shifting value, various parameter combinations are tried and scored.
   */
 
#include "afwarp.h"
 
#ifdef AF_CONFIG_OPTION_USE_WARPER
 
  /*************************************************************************/
  /*                                                                       */
  /* 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_afwarp
 
 
  /* The weights cover the range 0/64 - 63/64 of a pixel.  Obviously, */
  /* values around a half pixel (which means exactly between two grid */
  /* lines) gets the worst weight.                                    */
#if 1
  static const AF_WarpScore
  af_warper_weights[64] =
  {
    35, 32, 30, 25, 20, 15, 12, 10,  5,  1,  0,  0,  0,  0,  0,  0,
     0,  0,  0,  0,  0,  0, -1, -2, -5, -8,-10,-10,-20,-20,-30,-30,
 
   -30,-30,-20,-20,-10,-10, -8, -5, -2, -1,  0,  0,  0,  0,  0,  0,
     0,  0,  0,  0,  0,  0,  0,  1,  5, 10, 12, 15, 20, 25, 30, 32,
  };
#else
  static const AF_WarpScore
  af_warper_weights[64] =
  {
    30, 20, 10,  5,  4,  4,  3,  2,  1,  0,  0,  0,  0,  0,  0,  0,
     0,  0,  0,  0,  0,  0,  0, -1, -2, -2, -5, -5,-10,-10,-15,-20,
 
   -20,-15,-15,-10,-10, -5, -5, -2, -2, -1,  0,  0,  0,  0,  0,  0,
     0,  0,  0,  0,  0,  0,  0,  0,  1,  2,  3,  4,  4,  5, 10, 20,
  };
#endif
 
 
  /* Score segments for a given `scale' and `delta' in the range */
  /* `xx1' to `xx2', and store the best result in `warper'.  If  */
  /* the new best score is equal to the old one, prefer the      */
  /* value with a smaller distortion (around `base_distort').    */
 
  static void
  af_warper_compute_line_best( AF_Warper     warper,
                               FT_Fixed      scale,
                               FT_Pos        delta,
                               FT_Pos        xx1,
                               FT_Pos        xx2,
                               AF_WarpScore  base_distort,
                               AF_Segment    segments,
                               FT_Int        num_segments )
  {
    FT_Int        idx_min, idx_max, idx0;
    FT_Int        nn;
    AF_WarpScore  scores[65];
 
 
    for ( nn = 0; nn < 65; nn++ )
      scores[nn] = 0;
 
    idx0 = xx1 - warper->t1;
 
    /* compute minimum and maximum indices */
    {
      FT_Pos  xx1min = warper->x1min;
      FT_Pos  xx1max = warper->x1max;
      FT_Pos  w      = xx2 - xx1;
 
 
      if ( xx1min + w < warper->x2min )
        xx1min = warper->x2min - w;
 
      if ( xx1max + w > warper->x2max )
        xx1max = warper->x2max - w;
 
      idx_min = xx1min - warper->t1;
      idx_max = xx1max - warper->t1;
 
      if ( idx_min < 0 || idx_min > idx_max || idx_max > 64 )
      {
        FT_TRACE5(( "invalid indices:\n"
                    "  min=%d max=%d, xx1=%ld xx2=%ld,\n"
                    "  x1min=%ld x1max=%ld, x2min=%ld x2max=%ld\n",
                    idx_min, idx_max, xx1, xx2,
                    warper->x1min, warper->x1max,
                    warper->x2min, warper->x2max ));
        return;
      }
    }
 
    for ( nn = 0; nn < num_segments; nn++ )
    {
      FT_Pos  len = segments[nn].max_coord - segments[nn].min_coord;
      FT_Pos  y0  = FT_MulFix( segments[nn].pos, scale ) + delta;
      FT_Pos  y   = y0 + ( idx_min - idx0 );
      FT_Int  idx;
 
 
      /* score the length of the segments for the given range */
      for ( idx = idx_min; idx <= idx_max; idx++, y++ )
        scores[idx] += af_warper_weights[y & 63] * len;
    }
 
    /* find best score */
    {
      FT_Int  idx;
 
 
      for ( idx = idx_min; idx <= idx_max; idx++ )
      {
        AF_WarpScore  score = scores[idx];
        AF_WarpScore  distort = base_distort + ( idx - idx0 );
 
 
        if ( score > warper->best_score         ||
             ( score == warper->best_score    &&
               distort < warper->best_distort ) )
        {
          warper->best_score   = score;
          warper->best_distort = distort;
          warper->best_scale   = scale;
          warper->best_delta   = delta + ( idx - idx0 );
        }
      }
    }
  }
 
 
  /* Compute optimal scaling and delta values for a given glyph and */
  /* dimension.                                                     */
 
  FT_LOCAL_DEF( void )
  af_warper_compute( AF_Warper      warper,
                     AF_GlyphHints  hints,
                     AF_Dimension   dim,
                     FT_Fixed      *a_scale,
                     FT_Pos        *a_delta )
  {
    AF_AxisHints  axis;
    AF_Point      points;
 
    FT_Fixed      org_scale;
    FT_Pos        org_delta;
 
    FT_Int        nn, num_points, num_segments;
    FT_Int        X1, X2;
    FT_Int        w;
 
    AF_WarpScore  base_distort;
    AF_Segment    segments;
 
 
    /* get original scaling transformation */
    if ( dim == AF_DIMENSION_VERT )
    {
      org_scale = hints->y_scale;
      org_delta = hints->y_delta;
    }
    else
    {
      org_scale = hints->x_scale;
      org_delta = hints->x_delta;
    }
 
    warper->best_scale   = org_scale;
    warper->best_delta   = org_delta;
    warper->best_score   = FT_INT_MIN;
    warper->best_distort = 0;
 
    axis         = &hints->axis[dim];
    segments     = axis->segments;
    num_segments = axis->num_segments;
    points       = hints->points;
    num_points   = hints->num_points;
 
    *a_scale = org_scale;
    *a_delta = org_delta;
 
    /* get X1 and X2, minimum and maximum in original coordinates */
    if ( num_segments < 1 )
      return;
 
#if 1
    X1 = X2 = points[0].fx;
    for ( nn = 1; nn < num_points; nn++ )
    {
      FT_Int  X = points[nn].fx;
 
 
      if ( X < X1 )
        X1 = X;
      if ( X > X2 )
        X2 = X;
    }
#else
    X1 = X2 = segments[0].pos;
    for ( nn = 1; nn < num_segments; nn++ )
    {
      FT_Int  X = segments[nn].pos;
 
 
      if ( X < X1 )
        X1 = X;
      if ( X > X2 )
        X2 = X;
    }
#endif
 
    if ( X1 >= X2 )
      return;
 
    warper->x1 = FT_MulFix( X1, org_scale ) + org_delta;
    warper->x2 = FT_MulFix( X2, org_scale ) + org_delta;
 
    warper->t1 = AF_WARPER_FLOOR( warper->x1 );
    warper->t2 = AF_WARPER_CEIL( warper->x2 );
 
    /* examine a half pixel wide range around the maximum coordinates */
    warper->x1min = warper->x1 & ~31;
    warper->x1max = warper->x1min + 32;
    warper->x2min = warper->x2 & ~31;
    warper->x2max = warper->x2min + 32;
 
    if ( warper->x1max > warper->x2 )
      warper->x1max = warper->x2;
 
    if ( warper->x2min < warper->x1 )
      warper->x2min = warper->x1;
 
    warper->w0 = warper->x2 - warper->x1;
 
    if ( warper->w0 <= 64 )
    {
      warper->x1max = warper->x1;
      warper->x2min = warper->x2;
    }
 
    /* examine (at most) a pixel wide range around the natural width */
    warper->wmin = warper->x2min - warper->x1max;
    warper->wmax = warper->x2max - warper->x1min;
 
#if 1
    /* some heuristics to reduce the number of widths to be examined */
    {
      int  margin = 16;
 
 
      if ( warper->w0 <= 128 )
      {
         margin = 8;
         if ( warper->w0 <= 96 )
           margin = 4;
      }
 
      if ( warper->wmin < warper->w0 - margin )
        warper->wmin = warper->w0 - margin;
 
      if ( warper->wmax > warper->w0 + margin )
        warper->wmax = warper->w0 + margin;
    }
 
    if ( warper->wmin < warper->w0 * 3 / 4 )
      warper->wmin = warper->w0 * 3 / 4;
 
    if ( warper->wmax > warper->w0 * 5 / 4 )
      warper->wmax = warper->w0 * 5 / 4;
#else
    /* no scaling, just translation */
    warper->wmin = warper->wmax = warper->w0;
#endif
 
    for ( w = warper->wmin; w <= warper->wmax; w++ )
    {
      FT_Fixed  new_scale;
      FT_Pos    new_delta;
      FT_Pos    xx1, xx2;
 
 
      /* compute min and max positions for given width,       */
      /* assuring that they stay within the coordinate ranges */
      xx1 = warper->x1;
      xx2 = warper->x2;
      if ( w >= warper->w0 )
      {
        xx1 -= w - warper->w0;
        if ( xx1 < warper->x1min )
        {
          xx2 += warper->x1min - xx1;
          xx1  = warper->x1min;
        }
      }
      else
      {
        xx1 -= w - warper->w0;
        if ( xx1 > warper->x1max )
        {
          xx2 -= xx1 - warper->x1max;
          xx1  = warper->x1max;
        }
      }
 
      if ( xx1 < warper->x1 )
        base_distort = warper->x1 - xx1;
      else
        base_distort = xx1 - warper->x1;
 
      if ( xx2 < warper->x2 )
        base_distort += warper->x2 - xx2;
      else
        base_distort += xx2 - warper->x2;
 
      /* give base distortion a greater weight while scoring */
      base_distort *= 10;
 
      new_scale = org_scale + FT_DivFix( w - warper->w0, X2 - X1 );
      new_delta = xx1 - FT_MulFix( X1, new_scale );
 
      af_warper_compute_line_best( warper, new_scale, new_delta, xx1, xx2,
                                   base_distort,
                                   segments, num_segments );
    }
 
    {
      FT_Fixed  best_scale = warper->best_scale;
      FT_Pos    best_delta = warper->best_delta;
 
 
      hints->xmin_delta = FT_MulFix( X1, best_scale - org_scale )
                          + best_delta;
      hints->xmax_delta = FT_MulFix( X2, best_scale - org_scale )
                          + best_delta;
 
      *a_scale = best_scale;
      *a_delta = best_delta;
    }
  }
 
#else /* !AF_CONFIG_OPTION_USE_WARPER */
 
  /* ANSI C doesn't like empty source files */
  typedef int  _af_warp_dummy;
 
#endif /* !AF_CONFIG_OPTION_USE_WARPER */
 
/* END */