ref: 63abb4bc63b06e537d0827cda7912259798083f2
dir: /src/base/ftbbox.c/
/***************************************************************************/
/* */
/* ftbbox.c */
/* */
/* FreeType bbox computation (body). */
/* */
/* Copyright 1996-2001, 2002 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 component has a _single_ role: to compute exact outline bounding */
/* boxes. */
/* */
/*************************************************************************/
#include <ft2build.h>
#include FT_BBOX_H
#include FT_IMAGE_H
#include FT_OUTLINE_H
#include FT_INTERNAL_CALC_H
typedef struct TBBox_Rec_
{
FT_Vector last;
FT_BBox bbox;
} TBBox_Rec;
/*************************************************************************/
/* */
/* <Function> */
/* BBox_Move_To */
/* */
/* <Description> */
/* This function is used as a `move_to' and `line_to' emitter during */
/* FT_Outline_Decompose(). It simply records the destination point */
/* in `user->last'; no further computations are necessary since we */
/* the cbox as the starting bbox which must be refined. */
/* */
/* <Input> */
/* to :: A pointer to the destination vector. */
/* */
/* <InOut> */
/* user :: A pointer to the current walk context. */
/* */
/* <Return> */
/* Always 0. Needed for the interface only. */
/* */
static int
BBox_Move_To( FT_Vector* to,
TBBox_Rec* user )
{
user->last = *to;
return 0;
}
#define CHECK_X( p, bbox ) \
( p->x < bbox.xMin || p->x > bbox.xMax )
#define CHECK_Y( p, bbox ) \
( p->y < bbox.yMin || p->y > bbox.yMax )
/*************************************************************************/
/* */
/* <Function> */
/* BBox_Conic_Check */
/* */
/* <Description> */
/* Finds the extrema of a 1-dimensional conic Bezier curve and update */
/* a bounding range. This version uses direct computation, as it */
/* doesn't need square roots. */
/* */
/* <Input> */
/* y1 :: The start coordinate. */
/* y2 :: The coordinate of the control point. */
/* y3 :: The end coordinate. */
/* */
/* <InOut> */
/* min :: The address of the current minimum. */
/* max :: The address of the current maximum. */
/* */
static void
BBox_Conic_Check( FT_Pos y1,
FT_Pos y2,
FT_Pos y3,
FT_Pos* min,
FT_Pos* max )
{
if ( y1 <= y3 )
{
if ( y2 == y1 ) /* Flat arc */
goto Suite;
}
else if ( y1 < y3 )
{
if ( y2 >= y1 && y2 <= y3 ) /* Ascending arc */
goto Suite;
}
else
{
if ( y2 >= y3 && y2 <= y1 ) /* Descending arc */
{
y2 = y1;
y1 = y3;
y3 = y2;
goto Suite;
}
}
y1 = y3 = y1 - FT_MulDiv( y2 - y1, y2 - y1, y1 - 2*y2 + y3 );
Suite:
if ( y1 < *min ) *min = y1;
if ( y3 > *max ) *max = y3;
}
/*************************************************************************/
/* */
/* <Function> */
/* BBox_Conic_To */
/* */
/* <Description> */
/* This function is used as a `conic_to' emitter during */
/* FT_Raster_Decompose(). It checks a conic Bezier curve with the */
/* current bounding box, and computes its extrema if necessary to */
/* update it. */
/* */
/* <Input> */
/* control :: A pointer to a control point. */
/* to :: A pointer to the destination vector. */
/* */
/* <InOut> */
/* user :: The address of the current walk context. */
/* */
/* <Return> */
/* Always 0. Needed for the interface only. */
/* */
/* <Note> */
/* In the case of a non-monotonous arc, we compute directly the */
/* extremum coordinates, as it is sufficiently fast. */
/* */
static int
BBox_Conic_To( FT_Vector* control,
FT_Vector* to,
TBBox_Rec* user )
{
/* we don't need to check `to' since it is always an `on' point, thus */
/* within the bbox */
if ( CHECK_X( control, user->bbox ) )
BBox_Conic_Check( user->last.x,
control->x,
to->x,
&user->bbox.xMin,
&user->bbox.xMax );
if ( CHECK_Y( control, user->bbox ) )
BBox_Conic_Check( user->last.y,
control->y,
to->y,
&user->bbox.yMin,
&user->bbox.yMax );
user->last = *to;
return 0;
}
/*************************************************************************/
/* */
/* <Function> */
/* BBox_Cubic_Check */
/* */
/* <Description> */
/* Finds the extrema of a 1-dimensional cubic Bezier curve and */
/* updates a bounding range. This version uses splitting because we */
/* don't want to use square roots and extra accuracies. */
/* */
/* <Input> */
/* p1 :: The start coordinate. */
/* p2 :: The coordinate of the first control point. */
/* p3 :: The coordinate of the second control point. */
/* p4 :: The end coordinate. */
/* */
/* <InOut> */
/* min :: The address of the current minimum. */
/* max :: The address of the current maximum. */
/* */
#if 0
static void
BBox_Cubic_Check( FT_Pos p1,
FT_Pos p2,
FT_Pos p3,
FT_Pos p4,
FT_Pos* min,
FT_Pos* max )
{
FT_Pos stack[32*3 + 1], *arc;
arc = stack;
arc[0] = p1;
arc[1] = p2;
arc[2] = p3;
arc[3] = p4;
do
{
FT_Pos y1 = arc[0];
FT_Pos y2 = arc[1];
FT_Pos y3 = arc[2];
FT_Pos y4 = arc[3];
if ( y1 == y4 )
{
if ( y1 == y2 && y1 == y3 ) /* Flat */
goto Test;
}
else if ( y1 < y4 )
{
if ( y2 >= y1 && y2 <= y4 && y3 >= y1 && y3 <= y4 ) /* Ascending */
goto Test;
}
else
{
if ( y2 >= y4 && y2 <= y1 && y3 >= y4 && y3 <= y1 ) /* Descending */
{
y2 = y1;
y1 = y4;
y4 = y2;
goto Test;
}
}
/* Unknown direction -- split the arc in two */
arc[6] = y4;
arc[1] = y1 = ( y1 + y2 ) / 2;
arc[5] = y4 = ( y4 + y3 ) / 2;
y2 = ( y2 + y3 ) / 2;
arc[2] = y1 = ( y1 + y2 ) / 2;
arc[4] = y4 = ( y4 + y2 ) / 2;
arc[3] = ( y1 + y4 ) / 2;
arc += 3;
goto Suite;
Test:
if ( y1 < *min ) *min = y1;
if ( y4 > *max ) *max = y4;
arc -= 3;
Suite:
;
} while ( arc >= stack );
}
#else
static void
test_cubic_extrema( FT_Pos y1,
FT_Pos y2,
FT_Pos y3,
FT_Pos y4,
FT_Fixed u,
FT_Pos* min,
FT_Pos* max )
{
/* FT_Pos a = y4 - 3*y3 + 3*y2 - y1; */
FT_Pos b = y3 - 2*y2 + y1;
FT_Pos c = y2 - y1;
FT_Pos d = y1;
FT_Pos y;
FT_Fixed uu;
FT_UNUSED ( y4 );
/* The polynom is */
/* */
/* a*x^3 + 3b*x^2 + 3c*x + d . */
/* */
/* However, we also have */
/* */
/* dP/dx(u) = 0 , */
/* */
/* which implies that */
/* */
/* P(u) = b*u^2 + 2c*u + d */
if ( u > 0 && u < 0x10000L )
{
uu = FT_MulFix( u, u );
y = d + FT_MulFix( c, 2*u ) + FT_MulFix( b, uu );
if ( y < *min ) *min = y;
if ( y > *max ) *max = y;
}
}
static void
BBox_Cubic_Check( FT_Pos y1,
FT_Pos y2,
FT_Pos y3,
FT_Pos y4,
FT_Pos* min,
FT_Pos* max )
{
/* always compare first and last points */
if ( y1 < *min ) *min = y1;
else if ( y1 > *max ) *max = y1;
if ( y4 < *min ) *min = y4;
else if ( y4 > *max ) *max = y4;
/* now, try to see if there are split points here */
if ( y1 <= y4 )
{
/* flat or ascending arc test */
if ( y1 <= y2 && y2 <= y4 && y1 <= y3 && y3 <= y4 )
return;
}
else /* y1 > y4 */
{
/* descending arc test */
if ( y1 >= y2 && y2 >= y4 && y1 >= y3 && y3 >= y4 )
return;
}
/* There are some split points. Find them. */
{
FT_Pos a = y4 - 3*y3 + 3*y2 - y1;
FT_Pos b = y3 - 2*y2 + y1;
FT_Pos c = y2 - y1;
FT_Pos d;
FT_Fixed t;
/* We need to solve "ax^2+2bx+c" here, without floating points! */
/* The trick is to normalize to a different representation in order */
/* to use our 16.16 fixed point routines. */
/* */
/* We compute FT_MulFix(b,b) and FT_MulFix(a,c) after the */
/* the normalization. These values must fit into a single 16.16 */
/* value. */
/* */
/* We normalize a, b, and c to "8.16" fixed float values to ensure */
/* that their product is held in a "16.16" value. */
/* */
{
FT_ULong t1, t2;
int shift = 0;
/* Technical explanation of what's happening there. */
/* */
/* The following computation is based on the fact that for */
/* any value "y", if "n" is the position of the most */
/* significant bit of "abs(y)" (starting from 0 for the */
/* least significant bit), then y is in the range */
/* */
/* "-2^n..2^n-1" */
/* */
/* We want to shift "a", "b" and "c" concurrently in order */
/* to ensure that they all fit in 8.16 values, which maps */
/* to the integer range "-2^23..2^23-1". */
/* */
/* Necessarily, we need to shift "a", "b" and "c" so that */
/* the most significant bit of their absolute values is at */
/* _most_ at position 23. */
/* */
/* We begin by computing "t1" as the bitwise "or" of the */
/* absolute values of "a", "b", "c". */
/* */
t1 = (FT_ULong)((a >= 0) ? a : -a );
t2 = (FT_ULong)((b >= 0) ? b : -b );
t1 |= t2;
t2 = (FT_ULong)((c >= 0) ? c : -c );
t1 |= t2;
/* Now, the most significant bit of "t1" is sure to be the */
/* msb of one of "a", "b", "c", depending on which one is */
/* expressed in the greatest integer range. */
/* */
/* We now compute the "shift", by shifting "t1" as many */
/* times as necessary to move its msb to position 23. */
/* */
/* This corresponds to a value of t1 that is in the range */
/* 0x40_0000..0x7F_FFFF. */
/* */
/* Finally, we shift "a", "b" and "c" by the same amount. */
/* This ensures that all values are now in the range */
/* -2^23..2^23, i.e. that they are now expressed as 8.16 */
/* fixed float numbers. */
/* */
/* This also means that we are using 24 bits of precision */
/* to compute the zeros, independently of the range of */
/* the original polynom coefficients. */
/* */
/* This should ensure reasonably accurate values for the */
/* zeros. Note that the latter are only expressed with */
/* 16 bits when computing the extrema (the zeros need to */
/* be in 0..1 exclusive to be considered part of the arc). */
/* */
if ( t1 == 0 ) /* all coefficients are 0! */
return;
if ( t1 > 0x7FFFFFUL )
{
do
{
shift++;
t1 >>= 1;
} while ( t1 > 0x7FFFFFUL );
/* losing some bits of precision, but we use 24 of them */
/* for the computation anyway. */
a >>= shift;
b >>= shift;
c >>= shift;
}
else if ( t1 < 0x400000UL )
{
do
{
shift++;
t1 <<= 1;
} while ( t1 < 0x400000UL );
a <<= shift;
b <<= shift;
c <<= shift;
}
}
/* handle a == 0 */
if ( a == 0 )
{
if ( b != 0 )
{
t = - FT_DivFix( c, b ) / 2;
test_cubic_extrema( y1, y2, y3, y4, t, min, max );
}
}
else
{
/* solve the equation now */
d = FT_MulFix( b, b ) - FT_MulFix( a, c );
if ( d < 0 )
return;
if ( d == 0 )
{
/* there is a single split point at -b/a */
t = - FT_DivFix( b, a );
test_cubic_extrema( y1, y2, y3, y4, t, min, max );
}
else
{
/* there are two solutions; we need to filter them though */
d = FT_SqrtFixed( (FT_Int32)d );
t = - FT_DivFix( b - d, a );
test_cubic_extrema( y1, y2, y3, y4, t, min, max );
t = - FT_DivFix( b + d, a );
test_cubic_extrema( y1, y2, y3, y4, t, min, max );
}
}
}
}
#endif
/*************************************************************************/
/* */
/* <Function> */
/* BBox_Cubic_To */
/* */
/* <Description> */
/* This function is used as a `cubic_to' emitter during */
/* FT_Raster_Decompose(). It checks a cubic Bezier curve with the */
/* current bounding box, and computes its extrema if necessary to */
/* update it. */
/* */
/* <Input> */
/* control1 :: A pointer to the first control point. */
/* control2 :: A pointer to the second control point. */
/* to :: A pointer to the destination vector. */
/* */
/* <InOut> */
/* user :: The address of the current walk context. */
/* */
/* <Return> */
/* Always 0. Needed for the interface only. */
/* */
/* <Note> */
/* In the case of a non-monotonous arc, we don't compute directly */
/* extremum coordinates, we subdivise instead. */
/* */
static int
BBox_Cubic_To( FT_Vector* control1,
FT_Vector* control2,
FT_Vector* to,
TBBox_Rec* user )
{
/* we don't need to check `to' since it is always an `on' point, thus */
/* within the bbox */
if ( CHECK_X( control1, user->bbox ) ||
CHECK_X( control2, user->bbox ) )
BBox_Cubic_Check( user->last.x,
control1->x,
control2->x,
to->x,
&user->bbox.xMin,
&user->bbox.xMax );
if ( CHECK_Y( control1, user->bbox ) ||
CHECK_Y( control2, user->bbox ) )
BBox_Cubic_Check( user->last.y,
control1->y,
control2->y,
to->y,
&user->bbox.yMin,
&user->bbox.yMax );
user->last = *to;
return 0;
}
/* documentation is in ftbbox.h */
FT_EXPORT_DEF( FT_Error )
FT_Outline_Get_BBox( FT_Outline* outline,
FT_BBox *abbox )
{
FT_BBox cbox;
FT_BBox bbox;
FT_Vector* vec;
FT_UShort n;
if ( !abbox )
return FT_Err_Invalid_Argument;
if ( !outline )
return FT_Err_Invalid_Outline;
/* if outline is empty, return (0,0,0,0) */
if ( outline->n_points == 0 || outline->n_contours <= 0 )
{
abbox->xMin = abbox->xMax = 0;
abbox->yMin = abbox->yMax = 0;
return 0;
}
/* We compute the control box as well as the bounding box of */
/* all `on' points in the outline. Then, if the two boxes */
/* coincide, we exit immediately. */
vec = outline->points;
bbox.xMin = bbox.xMax = cbox.xMin = cbox.xMax = vec->x;
bbox.yMin = bbox.yMax = cbox.yMin = cbox.yMax = vec->y;
vec++;
for ( n = 1; n < outline->n_points; n++ )
{
FT_Pos x = vec->x;
FT_Pos y = vec->y;
/* update control box */
if ( x < cbox.xMin ) cbox.xMin = x;
if ( x > cbox.xMax ) cbox.xMax = x;
if ( y < cbox.yMin ) cbox.yMin = y;
if ( y > cbox.yMax ) cbox.yMax = y;
if ( FT_CURVE_TAG( outline->tags[n] ) == FT_CURVE_TAG_ON )
{
/* update bbox for `on' points only */
if ( x < bbox.xMin ) bbox.xMin = x;
if ( x > bbox.xMax ) bbox.xMax = x;
if ( y < bbox.yMin ) bbox.yMin = y;
if ( y > bbox.yMax ) bbox.yMax = y;
}
vec++;
}
/* test two boxes for equality */
if ( cbox.xMin < bbox.xMin || cbox.xMax > bbox.xMax ||
cbox.yMin < bbox.yMin || cbox.yMax > bbox.yMax )
{
/* the two boxes are different, now walk over the outline to */
/* get the Bezier arc extrema. */
static const FT_Outline_Funcs bbox_interface =
{
(FT_Outline_MoveTo_Func) BBox_Move_To,
(FT_Outline_LineTo_Func) BBox_Move_To,
(FT_Outline_ConicTo_Func)BBox_Conic_To,
(FT_Outline_CubicTo_Func)BBox_Cubic_To,
0, 0
};
FT_Error error;
TBBox_Rec user;
user.bbox = bbox;
error = FT_Outline_Decompose( outline, &bbox_interface, &user );
if ( error )
return error;
*abbox = user.bbox;
}
else
*abbox = bbox;
return FT_Err_Ok;
}
/* END */