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kc3-lang/freetype/src/base/ftbbox.c
Werner Lemberg
- src/base/ftbbox.c
-
/***************************************************************************/ /* */ /* ftbbox.c */ /* */ /* FreeType bbox computation (body). */ /* */ /* Copyright 1996-2001 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 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 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, &interface, &user ); if ( error ) return error; *abbox = user.bbox; } else *abbox = bbox; return FT_Err_Ok; } /* END */