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* src/sdf/ftsdf.c: More comments and code style fix.

This commit is contained in:
Anuj Verma 2020-07-01 18:34:59 +05:30 committed by anujverma
parent d0e3074738
commit be3b7d7945
2 changed files with 34 additions and 8 deletions
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8
[GSoC]ChangeLog
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@ -1,3 +1,11 @@
2020-07-01 Anuj Verma <anujv@iitbhilai.ac.in>
* src/sdf/ftsdf.c (get_min_distance_conic): Add more
details to why we clamp the roots.
* src/sdf/ftsdf.c: Make sure preprocessor # is always
on the first line.
2020-07-01 Anuj Verma <anujv@iitbhilai.ac.in>
[sdf] Make squared distances toggleable.

34
src/sdf/ftsdf.c
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@ -15,10 +15,10 @@
/* 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 is upto a */
/* 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
# define USE_SQUARED_DISTANCES 0
#endif
/**************************************************************************
@ -57,10 +57,10 @@
/* 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 ) + \
# 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 )
# define VECTOR_LENGTH_16D16( v ) FT_Vector_Length( &v )
#endif
/**************************************************************************
@ -1213,7 +1213,7 @@
FT_16D16 roots[3] = { 0, 0, 0 }; /* real roots of the cubic eq */
FT_16D16 min_factor; /* factor at `nearest_point' */
FT_16D16 cross; /* to determin the sign */
FT_16D16 cross; /* to determine the sign */
FT_16D16 min = FT_INT_MAX; /* shortest squared distance */
FT_UShort num_roots; /* number of real roots of cubic */
@ -1267,6 +1267,9 @@
num_roots = 2;
}
/* [OPTIMIZATION]: Check the roots, clamp them and discard */
/* duplicate roots. */
/* convert these values to 16.16 for further computation */
aA.x = FT_26D6_16D16( aA.x );
aA.y = FT_26D6_16D16( aA.y );
@ -1289,9 +1292,24 @@
FT_16D16_Vec curve_point;
FT_16D16_Vec dist_vector;
/* check this: https://lists.nongnu.org/archive/html/freetype-devel/2020-06/msg00147.html */
/* to see why we clamp the values and not check the endpoints */
/* Ideally we should discard the roots which are outside the */
/* range [0.0, 1.0] and check the endpoints of the bezier, but */
/* Behdad gave me a lemma: */
/* Lemma: */
/* * If the closest point on the curve [0, 1] is to the endpoint */
/* at t = 1 and the cubic has no real roots at t = 1 then, the */
/* cubic must have a real root at some t > 1. */
/* * Similarly, */
/* If the closest point on the curve [0, 1] is to the endpoint */
/* at t = 0 and the cubic has no real roots at t = 0 then, the */
/* cubic must have a real root at some t < 0. */
/* */
/* Now because of this lemma we only need to clamp the roots and */
/* that will take care of the endpoints. */
/* */
/* For proof contact: behdad@behdad.org */
/* For more details check message: */
/* https://lists.nongnu.org/archive/html/freetype-devel/2020-06/msg00147.html */
if ( t < 0 )
t = 0;
if ( t > FT_INT_16D16( 1 ) )