1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
|
/*
* Copyright © 2006 Red Hat, Inc.
*
* Permission to use, copy, modify, distribute, and sell this software
* and its documentation for any purpose is hereby granted without
* fee, provided that the above copyright notice appear in all copies
* and that both that copyright notice and this permission notice
* appear in supporting documentation, and that the name of
* Red Hat, Inc. not be used in advertising or publicity pertaining to
* distribution of the software without specific, written prior
* permission. Red Hat, Inc. makes no representations about the
* suitability of this software for any purpose. It is provided "as
* is" without express or implied warranty.
*
* RED HAT, INC. DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS
* SOFTWARE, INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND
* FITNESS, IN NO EVENT SHALL RED HAT, INC. BE LIABLE FOR ANY SPECIAL,
* INDIRECT OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER
* RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
* OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR
* IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
*
* Author: Carl D. Worth <cworth@cworth.org>
*/
#include "cairo-test.h"
/* This test exercises the various interactions between
* cairo_set_line_width and cairo_scale. Specifically it shows how
* separate transformations can affect the pen for stroking compared
* to the path itself.
*
* This was inspired by an image by Maxim Shemanarev demonstrating the
* flexible-pipeline nature of his Antigrain Geometry project:
*
* http://antigrain.com/tips/line_alignment/conv_order.gif
*
* It also uncovered some behavior in cairo that I found surprising.
* Namely, cairo_set_line_width was not transforming the width
* according the the current CTM, but instead delaying that
* transformation until the time of cairo_stroke.
*
* This delayed behavior was released in cairo 1.0 so we're going to
* document this as the way cairo_set_line_width works rather than
* considering this a bug.
*/
#define LINE_WIDTH 13
#define SPLINE 50.0
#define XSCALE 0.5
#define YSCALE 2.0
#define WIDTH (XSCALE * SPLINE * 6.0)
#define HEIGHT (YSCALE * SPLINE * 2.0)
static void
spline_path (cairo_t *cr)
{
cairo_save (cr);
{
cairo_move_to (cr,
- SPLINE, 0);
cairo_curve_to (cr,
- SPLINE / 4, - SPLINE,
SPLINE / 4, SPLINE,
SPLINE, 0);
}
cairo_restore (cr);
}
/* If we scale before setting the line width or creating the path,
* then obviously both will be scaled. */
static void
scale_then_set_line_width_and_stroke (cairo_t *cr)
{
cairo_scale (cr, XSCALE, YSCALE);
cairo_set_line_width (cr, LINE_WIDTH);
spline_path (cr);
cairo_stroke (cr);
}
/* This is used to verify the results of
* scale_then_set_line_width_and_stroke.
*
* It uses save/restore pairs to isolate the scaling of the path and
* line_width and ensures that both are scaled.
*/
static void
scale_path_and_line_width (cairo_t *cr)
{
cairo_save (cr);
{
cairo_scale (cr, XSCALE, YSCALE);
spline_path (cr);
}
cairo_restore (cr);
cairo_save (cr);
{
cairo_scale (cr, XSCALE, YSCALE);
cairo_set_line_width (cr, LINE_WIDTH);
cairo_stroke (cr);
}
cairo_restore (cr);
}
/* This is the case that was surprising.
*
* Setting the line width before scaling doesn't change anything. The
* line width will be interpreted under the CTM in effect at the time
* of cairo_stroke, so the line width will be scaled as well as the
* path here.
*/
static void
set_line_width_then_scale_and_stroke (cairo_t *cr)
{
cairo_set_line_width (cr, LINE_WIDTH);
cairo_scale (cr, XSCALE, YSCALE);
spline_path (cr);
cairo_stroke (cr);
}
/* Here then is the way to achieve the alternate result.
*
* This uses save/restore pairs to isolate the scaling of the path and
* line_width and ensures that the path is scaled while the line width
* is not.
*/
static void
scale_path_not_line_width (cairo_t *cr)
{
cairo_save (cr);
{
cairo_scale (cr, XSCALE, YSCALE);
spline_path (cr);
}
cairo_restore (cr);
cairo_save (cr);
{
cairo_set_line_width (cr, LINE_WIDTH);
cairo_stroke (cr);
}
cairo_restore (cr);
}
static cairo_test_status_t
draw (cairo_t *cr, int width, int height)
{
int i;
void (* const figures[4]) (cairo_t *cr) = {
scale_then_set_line_width_and_stroke,
scale_path_and_line_width,
set_line_width_then_scale_and_stroke,
scale_path_not_line_width
};
cairo_set_source_rgb (cr, 1.0, 1.0, 1.0); /* white */
cairo_paint (cr);
cairo_set_source_rgb (cr, 0.0, 0.0, 0.0); /* black */
for (i = 0; i < 4; i++) {
cairo_save (cr);
cairo_translate (cr,
WIDTH/4 + (i % 2) * WIDTH/2,
HEIGHT/4 + (i / 2) * HEIGHT/2);
(figures[i]) (cr);
cairo_restore (cr);
}
return CAIRO_TEST_SUCCESS;
}
CAIRO_TEST (line_width_scale,
"Tests interaction of cairo_set_line_width with cairo_scale",
"stroke", /* keywords */
NULL, /* requirements */
WIDTH, HEIGHT,
NULL, draw)
|
