Commit 7ad15d59265410139078d835181565b771e34c05
2011-02-20T07:30:46
[autofit] Document warper.
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diff --git a/src/autofit/afhints.c b/src/autofit/afhints.c
index 9859370..a68ce42 100644
--- a/src/autofit/afhints.c
+++ b/src/autofit/afhints.c
@@ -1152,6 +1152,8 @@
#ifdef AF_USE_WARPER
+ /* Apply (small) warp scale and warp delta for given dimension. */
+
FT_LOCAL_DEF( void )
af_glyph_hints_scale_dim( AF_GlyphHints hints,
AF_Dimension dim,
diff --git a/src/autofit/afwarp.c b/src/autofit/afwarp.c
index f5bb9b1..801ff31 100644
--- a/src/autofit/afwarp.c
+++ b/src/autofit/afwarp.c
@@ -4,7 +4,7 @@
/* */
/* Auto-fitter warping algorithm (body). */
/* */
-/* Copyright 2006, 2007 by */
+/* Copyright 2006, 2007, 2011 by */
/* David Turner, Robert Wilhelm, and Werner Lemberg. */
/* */
/* This file is part of the FreeType project, and may only be used, */
@@ -16,10 +16,20 @@
/***************************************************************************/
+ /*
+ * 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_USE_WARPER
+ /* 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] =
@@ -43,6 +53,11 @@
#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,
@@ -100,6 +115,7 @@
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;
}
@@ -115,9 +131,9 @@
AF_WarpScore distort = base_distort + ( idx - idx0 );
- if ( score > warper->best_score ||
+ if ( score > warper->best_score ||
( score == warper->best_score &&
- distort < warper->best_distort ) )
+ distort < warper->best_distort ) )
{
warper->best_score = score;
warper->best_distort = distort;
@@ -129,6 +145,9 @@
}
+ /* 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,
@@ -215,6 +234,7 @@
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;
@@ -234,10 +254,12 @@
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;
@@ -273,6 +295,8 @@
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 )
@@ -304,6 +328,7 @@
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 );
@@ -331,7 +356,7 @@
#else /* !AF_USE_WARPER */
-char af_warper_dummy = 0; /* make compiler happy */
+ char af_warper_dummy = 0; /* make compiler happy */
#endif /* !AF_USE_WARPER */