1 /* cairo - a vector graphics library with display and print output
3 * Copyright © 2005 Red Hat, Inc
5 * This library is free software; you can redistribute it and/or
6 * modify it either under the terms of the GNU Lesser General Public
7 * License version 2.1 as published by the Free Software Foundation
8 * (the "LGPL") or, at your option, under the terms of the Mozilla
9 * Public License Version 1.1 (the "MPL"). If you do not alter this
10 * notice, a recipient may use your version of this file under either
11 * the MPL or the LGPL.
13 * You should have received a copy of the LGPL along with this library
14 * in the file COPYING-LGPL-2.1; if not, write to the Free Software
15 * Foundation, Inc., 51 Franklin Street, Suite 500, Boston, MA 02110-1335, USA
16 * You should have received a copy of the MPL along with this library
17 * in the file COPYING-MPL-1.1
19 * The contents of this file are subject to the Mozilla Public License
20 * Version 1.1 (the "License"); you may not use this file except in
21 * compliance with the License. You may obtain a copy of the License at
22 * http://www.mozilla.org/MPL/
24 * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY
25 * OF ANY KIND, either express or implied. See the LGPL or the MPL for
26 * the specific language governing rights and limitations.
28 * The Original Code is the cairo graphics library.
30 * The Initial Developer of the Original Code is Red Hat, Inc.
33 * Carl Worth <cworth@cworth.org>
37 #include "cairo-error-private.h"
40 _cairo_stroke_style_init (cairo_stroke_style_t *style)
42 VG (VALGRIND_MAKE_MEM_UNDEFINED (style, sizeof (cairo_stroke_style_t)));
44 style->line_width = CAIRO_GSTATE_LINE_WIDTH_DEFAULT;
45 style->line_cap = CAIRO_GSTATE_LINE_CAP_DEFAULT;
46 style->line_join = CAIRO_GSTATE_LINE_JOIN_DEFAULT;
47 style->miter_limit = CAIRO_GSTATE_MITER_LIMIT_DEFAULT;
50 style->num_dashes = 0;
51 style->dash_offset = 0.0;
55 _cairo_stroke_style_init_copy (cairo_stroke_style_t *style,
56 const cairo_stroke_style_t *other)
58 if (CAIRO_INJECT_FAULT ())
59 return _cairo_error (CAIRO_STATUS_NO_MEMORY);
61 VG (VALGRIND_MAKE_MEM_UNDEFINED (style, sizeof (cairo_stroke_style_t)));
63 style->line_width = other->line_width;
64 style->line_cap = other->line_cap;
65 style->line_join = other->line_join;
66 style->miter_limit = other->miter_limit;
68 style->num_dashes = other->num_dashes;
70 if (other->dash == NULL) {
73 style->dash = _cairo_malloc_ab (style->num_dashes, sizeof (double));
74 if (unlikely (style->dash == NULL))
75 return _cairo_error (CAIRO_STATUS_NO_MEMORY);
77 memcpy (style->dash, other->dash,
78 style->num_dashes * sizeof (double));
81 style->dash_offset = other->dash_offset;
83 return CAIRO_STATUS_SUCCESS;
87 _cairo_stroke_style_fini (cairo_stroke_style_t *style)
92 style->num_dashes = 0;
94 VG (VALGRIND_MAKE_MEM_NOACCESS (style, sizeof (cairo_stroke_style_t)));
98 * For a stroke in the given style, compute the maximum distance
99 * from the path that vertices could be generated. In the case
100 * of rotation in the ctm, the distance will not be exact.
103 _cairo_stroke_style_max_distance_from_path (const cairo_stroke_style_t *style,
104 const cairo_path_fixed_t *path,
105 const cairo_matrix_t *ctm,
106 double *dx, double *dy)
108 double style_expansion = 0.5;
110 if (style->line_cap == CAIRO_LINE_CAP_SQUARE)
111 style_expansion = M_SQRT1_2;
113 if (style->line_join == CAIRO_LINE_JOIN_MITER &&
114 ! path->stroke_is_rectilinear &&
115 style_expansion < M_SQRT2 * style->miter_limit)
117 style_expansion = M_SQRT2 * style->miter_limit;
120 style_expansion *= style->line_width;
122 if (_cairo_matrix_has_unity_scale (ctm)) {
123 *dx = *dy = style_expansion;
125 *dx = style_expansion * hypot (ctm->xx, ctm->xy);
126 *dy = style_expansion * hypot (ctm->yy, ctm->yx);
131 * Computes the period of a dashed stroke style.
132 * Returns 0 for non-dashed styles.
135 _cairo_stroke_style_dash_period (const cairo_stroke_style_t *style)
141 for (i = 0; i < style->num_dashes; i++)
142 period += style->dash[i];
144 if (style->num_dashes & 1)
151 * Coefficient of the linear approximation (minimizing square difference)
152 * of the surface covered by round caps
154 * This can be computed in the following way:
155 * the area inside the circle with radius w/2 and the region -d/2 <= x <= d/2 is:
156 * f(w,d) = 2 * integrate (sqrt (w*w/4 - x*x), x, -d/2, d/2)
157 * The square difference to a generic linear approximation (c*d) in the range (0,w) would be:
158 * integrate ((f(w,d) - c*d)^2, d, 0, w)
159 * To minimize this difference it is sufficient to find a solution of the differential with
161 * solve ( diff (integrate ((f(w,d) - c*d)^2, d, 0, w), c), c)
162 * Which leads to c = 9/32*pi*w
163 * Since we're not interested in the true area, but just in a coverage extimate,
164 * we always divide the real area by the line width (w).
165 * The same computation for square caps would be
166 * f(w,d) = 2 * integrate(w/2, x, -d/2, d/2)
168 * but in this case it would not be an approximation, since f is already linear in d.
170 #define ROUND_MINSQ_APPROXIMATION (9*M_PI/32)
173 * Computes the length of the "on" part of a dashed stroke style,
174 * taking into account also line caps.
175 * Returns 0 for non-dashed styles.
178 _cairo_stroke_style_dash_stroked (const cairo_stroke_style_t *style)
180 double stroked, cap_scale;
183 switch (style->line_cap) {
184 default: ASSERT_NOT_REACHED;
185 case CAIRO_LINE_CAP_BUTT: cap_scale = 0.0; break;
186 case CAIRO_LINE_CAP_ROUND: cap_scale = ROUND_MINSQ_APPROXIMATION; break;
187 case CAIRO_LINE_CAP_SQUARE: cap_scale = 1.0; break;
191 if (style->num_dashes & 1) {
192 /* Each dash element is used both as on and as off. The order in which they are summed is
193 * irrelevant, so sum the coverage of one dash element, taken both on and off at each iteration */
194 for (i = 0; i < style->num_dashes; i++)
195 stroked += style->dash[i] + cap_scale * MIN (style->dash[i], style->line_width);
197 /* Even (0, 2, ...) dashes are on and simply counted for the coverage, odd dashes are off, thus
198 * their coverage is approximated based on the area covered by the caps of adjacent on dases. */
199 for (i = 0; i + 1 < style->num_dashes; i += 2)
200 stroked += style->dash[i] + cap_scale * MIN (style->dash[i+1], style->line_width);
207 * Verifies if _cairo_stroke_style_dash_approximate should be used to generate
208 * an approximation of the dash pattern in the specified style, when used for
209 * stroking a path with the given CTM and tolerance.
210 * Always %FALSE for non-dashed styles.
213 _cairo_stroke_style_dash_can_approximate (const cairo_stroke_style_t *style,
214 const cairo_matrix_t *ctm,
219 if (! style->num_dashes)
222 period = _cairo_stroke_style_dash_period (style);
223 return _cairo_matrix_transformed_circle_major_axis (ctm, period) < tolerance;
227 * Create a 2-dashes approximation of a dashed style, by making the "on" and "off"
228 * parts respect the original ratio.
231 _cairo_stroke_style_dash_approximate (const cairo_stroke_style_t *style,
232 const cairo_matrix_t *ctm,
236 unsigned int *num_dashes)
238 double coverage, scale, offset;
239 cairo_bool_t on = TRUE;
242 coverage = _cairo_stroke_style_dash_stroked (style) / _cairo_stroke_style_dash_period (style);
243 coverage = MIN (coverage, 1.0);
244 scale = tolerance / _cairo_matrix_transformed_circle_major_axis (ctm, 1.0);
246 /* We stop searching for a starting point as soon as the
247 * offset reaches zero. Otherwise when an initial dash
248 * segment shrinks to zero it will be skipped over. */
249 offset = style->dash_offset;
250 while (offset > 0.0 && offset >= style->dash[i]) {
251 offset -= style->dash[i];
253 if (++i == style->num_dashes)
260 * We want to create a new dash pattern with the same relative coverage,
261 * but composed of just 2 elements with total length equal to scale.
262 * Based on the formula in _cairo_stroke_style_dash_stroked:
263 * scale * coverage = dashes[0] + cap_scale * MIN (dashes[1], line_width)
264 * = MIN (dashes[0] + cap_scale * (scale - dashes[0]),
265 * dashes[0] + cap_scale * line_width) =
266 * = MIN (dashes[0] * (1 - cap_scale) + cap_scale * scale,
267 * dashes[0] + cap_scale * line_width)
269 * Solving both cases we get:
270 * dashes[0] = scale * (coverage - cap_scale) / (1 - cap_scale)
271 * when scale - dashes[0] <= line_width
272 * dashes[0] = scale * coverage - cap_scale * line_width
273 * when scale - dashes[0] > line_width.
275 * Comparing the two cases we get:
277 * second > scale * (coverage - cap_scale) / (1 - cap_scale)
278 * second - cap_scale * second - scale * coverage + scale * cap_scale > 0
279 * (scale * coverage - cap_scale * line_width) - cap_scale * second - scale * coverage + scale * cap_scale > 0
280 * - line_width - second + scale > 0
281 * scale - second > line_width
282 * which is the condition for the second solution to be the valid one.
283 * So when second > first, the second solution is the correct one (i.e.
284 * the solution is always MAX (first, second).
286 switch (style->line_cap) {
292 case CAIRO_LINE_CAP_BUTT:
293 /* Simplified formula (substituting 0 for cap_scale): */
294 dashes[0] = scale * coverage;
297 case CAIRO_LINE_CAP_ROUND:
298 dashes[0] = MAX(scale * (coverage - ROUND_MINSQ_APPROXIMATION) / (1.0 - ROUND_MINSQ_APPROXIMATION),
299 scale * coverage - ROUND_MINSQ_APPROXIMATION * style->line_width);
302 case CAIRO_LINE_CAP_SQUARE:
304 * Special attention is needed to handle the case cap_scale == 1 (since the first solution
305 * is either indeterminate or -inf in this case). Since dash lengths are always >=0, using
306 * 0 as first solution always leads to the correct solution.
308 dashes[0] = MAX(0.0, scale * coverage - style->line_width);
312 dashes[1] = scale - dashes[0];
314 *dash_offset = on ? 0.0 : dashes[0];