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Diffstat (limited to 'src/libs/libgroff/geometry.cpp')
| -rw-r--r-- | src/libs/libgroff/geometry.cpp | 180 |
1 files changed, 180 insertions, 0 deletions
diff --git a/src/libs/libgroff/geometry.cpp b/src/libs/libgroff/geometry.cpp new file mode 100644 index 0000000..c4665c4 --- /dev/null +++ b/src/libs/libgroff/geometry.cpp @@ -0,0 +1,180 @@ +// -*- C++ -*- +/* Copyright (C) 1989-2020 Free Software Foundation, Inc. + Written by Gaius Mulley <gaius@glam.ac.uk> + using adjust_arc_center() from printer.cpp, written by James Clark. + +This file is part of groff. + +groff is free software; you can redistribute it and/or modify it under +the terms of the GNU General Public License as published by the Free +Software Foundation, either version 3 of the License, or +(at your option) any later version. + +groff is distributed in the hope that it will be useful, but WITHOUT ANY +WARRANTY; without even the implied warranty of MERCHANTABILITY or +FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License +for more details. + +You should have received a copy of the GNU General Public License +along with this program. If not, see <http://www.gnu.org/licenses/>. */ + +#ifdef HAVE_CONFIG_H +#include "config.h" +#endif + +#include <stdio.h> +#include <math.h> + +#undef MAX +#define MAX(a, b) (((a) > (b)) ? (a) : (b)) + +#undef MIN +#define MIN(a, b) (((a) < (b)) ? (a) : (b)) + + +// This utility function adjusts the specified center of the +// arc so that it is equidistant between the specified start +// and end points. (p[0], p[1]) is a vector from the current +// point to the center; (p[2], p[3]) is a vector from the +// center to the end point. If the center can be adjusted, +// a vector from the current point to the adjusted center is +// stored in c[0], c[1] and 1 is returned. Otherwise 0 is +// returned. + +#if 1 +int adjust_arc_center(const int *p, double *c) +{ + // We move the center along a line parallel to the line between + // the specified start point and end point so that the center + // is equidistant between the start and end point. + // It can be proved (using Lagrange multipliers) that this will + // give the point nearest to the specified center that is equidistant + // between the start and end point. + + double x = p[0] + p[2]; // (x, y) is the end point + double y = p[1] + p[3]; + double n = x*x + y*y; + if (n != 0) { + c[0]= double(p[0]); + c[1] = double(p[1]); + double k = .5 - (c[0]*x + c[1]*y)/n; + c[0] += k*x; + c[1] += k*y; + return 1; + } + else + return 0; +} +#else +int printer::adjust_arc_center(const int *p, double *c) +{ + int x = p[0] + p[2]; // (x, y) is the end point + int y = p[1] + p[3]; + // Start at the current point; go in the direction of the specified + // center point until we reach a point that is equidistant between + // the specified starting point and the specified end point. Place + // the center of the arc there. + double n = p[0]*double(x) + p[1]*double(y); + if (n > 0) { + double k = (double(x)*x + double(y)*y)/(2.0*n); + // (cx, cy) is our chosen center + c[0] = k*p[0]; + c[1] = k*p[1]; + return 1; + } + else { + // We would never reach such a point. So instead start at the + // specified end point of the arc. Go towards the specified + // center point until we reach a point that is equidistant between + // the specified start point and specified end point. Place + // the center of the arc there. + n = p[2]*double(x) + p[3]*double(y); + if (n > 0) { + double k = 1 - (double(x)*x + double(y)*y)/(2.0*n); + // (c[0], c[1]) is our chosen center + c[0] = p[0] + k*p[2]; + c[1] = p[1] + k*p[3]; + return 1; + } + else + return 0; + } +} +#endif + + +/* + * check_output_arc_limits - works out the smallest box that will encompass + * an arc defined by an origin (x, y) and two + * vectors (p0, p1) and (p2, p3). + * (x1, y1) -> start of arc + * (x1, y1) + (xv1, yv1) -> center of circle + * (x1, y1) + (xv1, yv1) + (xv2, yv2) -> end of arc + * + * Works out in which quadrant the arc starts and + * stops, and from this it determines the x, y + * max/min limits. The arc is drawn clockwise. + */ + +void check_output_arc_limits(int x_1, int y_1, + int xv_1, int yv_1, + int xv_2, int yv_2, + double c_0, double c_1, + int *minx, int *maxx, + int *miny, int *maxy) +{ + int radius = (int)sqrt(c_0 * c_0 + c_1 * c_1); + // clockwise direction + int xcenter = x_1 + xv_1; + int ycenter = y_1 + yv_1; + int xend = xcenter + xv_2; + int yend = ycenter + yv_2; + // for convenience, transform to counterclockwise direction, + // centered at the origin + int xs = xend - xcenter; + int ys = yend - ycenter; + int xe = x_1 - xcenter; + int ye = y_1 - ycenter; + *minx = *maxx = xs; + *miny = *maxy = ys; + if (xe > *maxx) + *maxx = xe; + else if (xe < *minx) + *minx = xe; + if (ye > *maxy) + *maxy = ye; + else if (ye < *miny) + *miny = ye; + int qs, qe; // quadrants 0..3 + if (xs >= 0) + qs = (ys >= 0) ? 0 : 3; + else + qs = (ys >= 0) ? 1 : 2; + if (xe >= 0) + qe = (ye >= 0) ? 0 : 3; + else + qe = (ye >= 0) ? 1 : 2; + // make qs always smaller than qe + if ((qs > qe) + || ((qs == qe) && (double(xs) * ye < double(xe) * ys))) + qe += 4; + for (int i = qs; i < qe; i++) + switch (i % 4) { + case 0: + *maxy = radius; + break; + case 1: + *minx = -radius; + break; + case 2: + *miny = -radius; + break; + case 3: + *maxx = radius; + break; + } + *minx += xcenter; + *maxx += xcenter; + *miny += ycenter; + *maxy += ycenter; +} |