summaryrefslogtreecommitdiff
path: root/examples/cairotwisted.c
blob: 27b9fb0446194618c64c7909e9db6b771d6e46f8 (plain)
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
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
/* Example code to show how to use pangocairo to render text
 * projected on a path.
 *
 *
 * Written by Behdad Esfahbod, 2006..2007
 *
 * Permission to use, copy, modify, distribute, and sell this example
 * for any purpose is hereby granted without fee.
 * It is provided "as is" without express or implied warranty.
 */

#include <math.h>
#include <stdlib.h>
#include <pango/pangocairo.h>

void fancy_cairo_stroke (cairo_t *cr);
void fancy_cairo_stroke_preserve (cairo_t *cr);

/* A fancy cairo_stroke[_preserve]() that draws points and control
 * points, and connects them together.
 */
static void
_fancy_cairo_stroke (cairo_t *cr, cairo_bool_t preserve)
{
  int i;
  double line_width;
  cairo_path_t *path;
  cairo_path_data_t *data;
  const double dash[] = {10, 10};

  cairo_save (cr);
  cairo_set_source_rgb (cr, 1.0, 0.0, 0.0);

  line_width = cairo_get_line_width (cr);
  path = cairo_copy_path (cr);
  cairo_new_path (cr);

  cairo_save (cr);
  cairo_set_line_width (cr, line_width / 3);
  cairo_set_dash (cr, dash, G_N_ELEMENTS (dash), 0);
  for (i=0; i < path->num_data; i += path->data[i].header.length) {
    data = &path->data[i];
    switch (data->header.type) {
    case CAIRO_PATH_MOVE_TO:
    case CAIRO_PATH_LINE_TO:
	cairo_move_to (cr, data[1].point.x, data[1].point.y);
	break;
    case CAIRO_PATH_CURVE_TO:
	cairo_line_to (cr, data[1].point.x, data[1].point.y);
	cairo_move_to (cr, data[2].point.x, data[2].point.y);
	cairo_line_to (cr, data[3].point.x, data[3].point.y);
	break;
    case CAIRO_PATH_CLOSE_PATH:
	break;
    default:
	g_assert_not_reached ();
    }
  }
  cairo_stroke (cr);
  cairo_restore (cr);

  cairo_save (cr);
  cairo_set_line_width (cr, line_width * 4);
  cairo_set_line_cap (cr, CAIRO_LINE_CAP_ROUND);
  for (i=0; i < path->num_data; i += path->data[i].header.length) {
    data = &path->data[i];
    switch (data->header.type) {
    case CAIRO_PATH_MOVE_TO:
	cairo_move_to (cr, data[1].point.x, data[1].point.y);
	break;
    case CAIRO_PATH_LINE_TO:
	cairo_rel_line_to (cr, 0, 0);
	cairo_move_to (cr, data[1].point.x, data[1].point.y);
	break;
    case CAIRO_PATH_CURVE_TO:
	cairo_rel_line_to (cr, 0, 0);
	cairo_move_to (cr, data[1].point.x, data[1].point.y);
	cairo_rel_line_to (cr, 0, 0);
	cairo_move_to (cr, data[2].point.x, data[2].point.y);
	cairo_rel_line_to (cr, 0, 0);
	cairo_move_to (cr, data[3].point.x, data[3].point.y);
	break;
    case CAIRO_PATH_CLOSE_PATH:
	cairo_rel_line_to (cr, 0, 0);
	break;
    default:
	g_assert_not_reached ();
    }
  }
  cairo_rel_line_to (cr, 0, 0);
  cairo_stroke (cr);
  cairo_restore (cr);

  for (i=0; i < path->num_data; i += path->data[i].header.length) {
    data = &path->data[i];
    switch (data->header.type) {
    case CAIRO_PATH_MOVE_TO:
	cairo_move_to (cr, data[1].point.x, data[1].point.y);
	break;
    case CAIRO_PATH_LINE_TO:
	cairo_line_to (cr, data[1].point.x, data[1].point.y);
	break;
    case CAIRO_PATH_CURVE_TO:
	cairo_curve_to (cr, data[1].point.x, data[1].point.y,
			    data[2].point.x, data[2].point.y,
			    data[3].point.x, data[3].point.y);
	break;
    case CAIRO_PATH_CLOSE_PATH:
	cairo_close_path (cr);
	break;
    default:
	g_assert_not_reached ();
    }
  }
  cairo_stroke (cr);

  if (preserve)
    cairo_append_path (cr, path);

  cairo_path_destroy (path);

  cairo_restore (cr);
}

/* A fancy cairo_stroke() that draws points and control points, and
 * connects them together.
 */
void
fancy_cairo_stroke (cairo_t *cr)
{
  _fancy_cairo_stroke (cr, FALSE);
}

/* A fancy cairo_stroke_preserve() that draws points and control
 * points, and connects them together.
 */
void
fancy_cairo_stroke_preserve (cairo_t *cr)
{
  _fancy_cairo_stroke (cr, TRUE);
}


/* Returns Euclidean distance between two points */
static double
two_points_distance (cairo_path_data_t *a, cairo_path_data_t *b)
{
  double dx, dy;

  dx = b->point.x - a->point.x;
  dy = b->point.y - a->point.y;

  return sqrt (dx * dx + dy * dy);
}

/* Returns length of a Bezier curve.
 * Seems like computing that analytically is not easy.  The
 * code just flattens the curve using cairo and adds the length
 * of segments.
 */
static double
curve_length (double x0, double y0,
	      double x1, double y1,
	      double x2, double y2,
	      double x3, double y3)
{
  cairo_surface_t *surface;
  cairo_t *cr;
  cairo_path_t *path;
  cairo_path_data_t *data, current_point;
  int i;
  double length;

  surface = cairo_image_surface_create (CAIRO_FORMAT_A8, 0, 0);
  cr = cairo_create (surface);
  cairo_surface_destroy (surface);

  cairo_move_to (cr, x0, y0);
  cairo_curve_to (cr, x1, y1, x2, y2, x3, y3);

  length = 0;
  path = cairo_copy_path_flat (cr);
  for (i=0; i < path->num_data; i += path->data[i].header.length) {
    data = &path->data[i];
    switch (data->header.type) {

    case CAIRO_PATH_MOVE_TO:
	current_point = data[1];
	break;

    case CAIRO_PATH_LINE_TO:
	length += two_points_distance (&current_point, &data[1]);
	current_point = data[1];
	break;

    default:
    case CAIRO_PATH_CURVE_TO:
    case CAIRO_PATH_CLOSE_PATH:
	g_assert_not_reached ();
    }
  }
  cairo_path_destroy (path);

  cairo_destroy (cr);

  return length;
}


typedef double parametrization_t;

/* Compute parametrization info.  That is, for each part of the 
 * cairo path, tags it with its length.
 *
 * Free returned value with g_free().
 */
static parametrization_t *
parametrize_path (cairo_path_t *path)
{
  int i;
  cairo_path_data_t *data, last_move_to, current_point;
  parametrization_t *parametrization;

  parametrization = g_malloc (path->num_data * sizeof (parametrization[0]));

  for (i=0; i < path->num_data; i += path->data[i].header.length) {
    data = &path->data[i];
    parametrization[i] = 0.0;
    switch (data->header.type) {
    case CAIRO_PATH_MOVE_TO:
	last_move_to = data[1];
	current_point = data[1];
	break;
    case CAIRO_PATH_CLOSE_PATH:
	/* Make it look like it's a line_to to last_move_to */
	data = (&last_move_to) - 1;
	/* fall through */
    case CAIRO_PATH_LINE_TO:
	parametrization[i] = two_points_distance (&current_point, &data[1]);
	current_point = data[1];
	break;
    case CAIRO_PATH_CURVE_TO:
	/* naive curve-length, treating bezier as three line segments:
	parametrization[i] = two_points_distance (&current_point, &data[1])
			   + two_points_distance (&data[1], &data[2])
			   + two_points_distance (&data[2], &data[3]);
	*/
	parametrization[i] = curve_length (current_point.point.x, current_point.point.x,
					   data[1].point.x, data[1].point.y,
					   data[2].point.x, data[2].point.y,
					   data[3].point.x, data[3].point.y);

	current_point = data[3];
	break;
    default:
	g_assert_not_reached ();
    }
  }

  return parametrization;
}


typedef void (*transform_point_func_t) (void *closure, double *x, double *y);

/* Project a path using a function.  Each point of the path (including
 * Bezier control points) is passed to the function for transformation.
 */
static void
transform_path (cairo_path_t *path, transform_point_func_t f, void *closure)
{
  int i;
  cairo_path_data_t *data;

  for (i=0; i < path->num_data; i += path->data[i].header.length) {
    data = &path->data[i];
    switch (data->header.type) {
    case CAIRO_PATH_CURVE_TO:
      f (closure, &data[3].point.x, &data[3].point.y);
      f (closure, &data[2].point.x, &data[2].point.y);
    case CAIRO_PATH_MOVE_TO:
    case CAIRO_PATH_LINE_TO:
      f (closure, &data[1].point.x, &data[1].point.y);
      break;
    case CAIRO_PATH_CLOSE_PATH:
      break;
    default:
	g_assert_not_reached ();
    }
  }
}


/* Simple struct to hold a path and its parametrization */
typedef struct {
  cairo_path_t *path;
  parametrization_t *parametrization;
} parametrized_path_t;


/* Project a point X,Y onto a parameterized path.  The final point is
 * where you get if you walk on the path forward from the beginning for X
 * units, then stop there and walk another Y units perpendicular to the
 * path at that point.  In more detail:
 *
 * There's three pieces of math involved:
 *
 *   - The parametric form of the Line equation
 *     http://en.wikipedia.org/wiki/Line
 *
 *   - The parametric form of the Cubic Bézier curve equation
 *     http://en.wikipedia.org/wiki/B%C3%A9zier_curve
 *
 *   - The Gradient (aka multi-dimensional derivative) of the above
 *     http://en.wikipedia.org/wiki/Gradient
 *
 * The parametric forms are used to answer the question of "where will I be
 * if I walk a distance of X on this path".  The Gradient is used to answer
 * the question of "where will I be if then I stop, rotate left for 90
 * degrees and walk straight for a distance of Y".
 */
static void
point_on_path (parametrized_path_t *param,
	       double *x, double *y)
{
  int i;
  double ratio, the_y = *y, the_x = *x, dx, dy;
  cairo_path_data_t *data, last_move_to, current_point;
  cairo_path_t *path = param->path;
  parametrization_t *parametrization = param->parametrization;

  for (i=0; i + path->data[i].header.length < path->num_data &&
	    (the_x > parametrization[i] ||
	     path->data[i].header.type == CAIRO_PATH_MOVE_TO);
       i += path->data[i].header.length) {
    the_x -= parametrization[i];
    data = &path->data[i];
    switch (data->header.type) {
    case CAIRO_PATH_MOVE_TO:
	current_point = data[1];
        last_move_to = data[1];
	break;
    case CAIRO_PATH_LINE_TO:
	current_point = data[1];
	break;
    case CAIRO_PATH_CURVE_TO:
	current_point = data[3];
	break;
    case CAIRO_PATH_CLOSE_PATH:
	break;
    default:
	g_assert_not_reached ();
    }
  }
  data = &path->data[i];

  switch (data->header.type) {

  case CAIRO_PATH_MOVE_TO:
      break;
  case CAIRO_PATH_CLOSE_PATH:
      /* Make it look like it's a line_to to last_move_to */
      data = (&last_move_to) - 1;
      /* fall through */
  case CAIRO_PATH_LINE_TO:
      {
	ratio = the_x / parametrization[i];
	/* Line polynomial */
	*x = current_point.point.x * (1 - ratio) + data[1].point.x * ratio;
	*y = current_point.point.y * (1 - ratio) + data[1].point.y * ratio;

	/* Line gradient */
	dx = -(current_point.point.x - data[1].point.x);
	dy = -(current_point.point.y - data[1].point.y);

	/*optimization for: ratio = the_y / sqrt (dx * dx + dy * dy);*/
	ratio = the_y / parametrization[i];
	*x += -dy * ratio;
	*y +=  dx * ratio;
      }
      break;
  case CAIRO_PATH_CURVE_TO:
      {
	/* FIXME the formulas here are not exactly what we want, because the
	 * Bezier parametrization is not uniform.  But I don't know how to do
	 * better.  The caller can do slightly better though, by flattening the
	 * Bezier and avoiding this branch completely.  That has its own cost
	 * though, as large y values magnify the flattening error drastically.
	 */

        double ratio_1_0, ratio_0_1;
	double ratio_2_0, ratio_0_2;
	double ratio_3_0, ratio_2_1, ratio_1_2, ratio_0_3;
	double _1__4ratio_1_0_3ratio_2_0, _2ratio_1_0_3ratio_2_0;

	ratio = the_x / parametrization[i];

	ratio_1_0 = ratio;
	ratio_0_1 = 1 - ratio;

	ratio_2_0 = ratio_1_0 * ratio_1_0; /*      ratio  *      ratio  */
	ratio_0_2 = ratio_0_1 * ratio_0_1; /* (1 - ratio) * (1 - ratio) */

	ratio_3_0 = ratio_2_0 * ratio_1_0; /*      ratio  *      ratio  *      ratio  */
	ratio_2_1 = ratio_2_0 * ratio_0_1; /*      ratio  *      ratio  * (1 - ratio) */
	ratio_1_2 = ratio_1_0 * ratio_0_2; /*      ratio  * (1 - ratio) * (1 - ratio) */
	ratio_0_3 = ratio_0_1 * ratio_0_2; /* (1 - ratio) * (1 - ratio) * (1 - ratio) */

	_1__4ratio_1_0_3ratio_2_0 = 1 - 4 * ratio_1_0 + 3 * ratio_2_0;
	_2ratio_1_0_3ratio_2_0    =     2 * ratio_1_0 - 3 * ratio_2_0;

	/* Bezier polynomial */
	*x = current_point.point.x * ratio_0_3
	   + 3 *   data[1].point.x * ratio_1_2
	   + 3 *   data[2].point.x * ratio_2_1
	   +       data[3].point.x * ratio_3_0;
	*y = current_point.point.y * ratio_0_3
	   + 3 *   data[1].point.y * ratio_1_2
	   + 3 *   data[2].point.y * ratio_2_1
	   +       data[3].point.y * ratio_3_0;

	/* Bezier gradient */
	dx =-3 * current_point.point.x * ratio_0_2
	   + 3 *       data[1].point.x * _1__4ratio_1_0_3ratio_2_0
	   + 3 *       data[2].point.x * _2ratio_1_0_3ratio_2_0
	   + 3 *       data[3].point.x * ratio_2_0;
	dy =-3 * current_point.point.y * ratio_0_2
	   + 3 *       data[1].point.y * _1__4ratio_1_0_3ratio_2_0
	   + 3 *       data[2].point.y * _2ratio_1_0_3ratio_2_0
	   + 3 *       data[3].point.y * ratio_2_0;

	ratio = the_y / sqrt (dx * dx + dy * dy);
	*x += -dy * ratio;
	*y +=  dx * ratio;
      }
      break;
  default:
      g_assert_not_reached ();
  }
}

/* Projects the current path of cr onto the provided path. */
static void
map_path_onto (cairo_t *cr, cairo_path_t *path)
{
  cairo_path_t *current_path;
  parametrized_path_t param;

  param.path = path;
  param.parametrization = parametrize_path (path);

  current_path = cairo_copy_path (cr);
  cairo_new_path (cr);

  transform_path (current_path,
		  (transform_point_func_t) point_on_path, &param);

  cairo_append_path (cr, current_path);

  g_free (param.parametrization);
}


typedef void (*draw_path_func_t) (cairo_t *cr);

static void
draw_text (cairo_t *cr,
	   double x,
	   double y,
	   const char *font,
	   const char *text)
{
  PangoLayout *layout;
  PangoLayoutLine *line;
  PangoFontDescription *desc;
  cairo_font_options_t *font_options;

  font_options = cairo_font_options_create ();

  cairo_font_options_set_hint_style (font_options, CAIRO_HINT_STYLE_NONE);
  cairo_font_options_set_hint_metrics (font_options, CAIRO_HINT_METRICS_OFF);

  cairo_set_font_options (cr, font_options);
  cairo_font_options_destroy (font_options);

  layout = pango_cairo_create_layout (cr);

  desc = pango_font_description_from_string (font);
  pango_layout_set_font_description (layout, desc);
  pango_font_description_free (desc);

  pango_layout_set_text (layout, text, -1);

  /* Use pango_layout_get_line() instead of pango_layout_get_line_readonly()
   * for older versions of pango
   */
  line = pango_layout_get_line_readonly (layout, 0);

  cairo_move_to (cr, x, y);
  pango_cairo_layout_line_path (cr, line);

  g_object_unref (layout);
}

static void
draw_twisted (cairo_t *cr,
	      double x,
	      double y,
	      const char *font,
	      const char *text)
{
  cairo_path_t *path;

  cairo_save (cr);

  /* Decrease tolerance a bit, since it's going to be magnified */
  cairo_set_tolerance (cr, 0.01);

  /* Using cairo_copy_path() here shows our deficiency in handling
   * Bezier curves, specially around sharper curves.
   *
   * Using cairo_copy_path_flat() on the other hand, magnifies the
   * flattening error with large off-path values.  We decreased
   * tolerance for that reason.  Increase tolerance to see that
   * artifact.
   */
  path = cairo_copy_path_flat (cr);
/*path = cairo_copy_path (cr);*/

  cairo_new_path (cr);

  draw_text (cr, x, y, font, text);
  map_path_onto (cr, path);

  cairo_fill_preserve (cr);

  cairo_save (cr);
  cairo_set_source_rgb (cr, 0.1, 0.1, 0.1);
  cairo_stroke (cr);
  cairo_restore (cr);

  cairo_restore (cr);
}

static void
draw_dream (cairo_t *cr)
{
  cairo_move_to (cr, 50, 650);

  cairo_rel_line_to (cr, 250, 50);
  cairo_rel_curve_to (cr, 250, 50, 600, -50, 600, -250);
  cairo_rel_curve_to (cr, 0, -400, -300, -100, -800, -300);

  cairo_set_line_width (cr, 1.5);
  cairo_set_source_rgba (cr, 0.3, 0.3, 1.0, 0.3);

  fancy_cairo_stroke_preserve (cr);

  draw_twisted (cr,
		0, 0,
		"Serif 72",
		"It was a dream... Oh Just a dream...");
}

static void
draw_wow (cairo_t *cr)
{
  cairo_move_to (cr, 400, 780);

  cairo_rel_curve_to (cr, 50, -50, 150, -50, 200, 0);

  cairo_scale (cr, 1.0, 2.0);
  cairo_set_line_width (cr, 2.0);
  cairo_set_source_rgba (cr, 0.3, 1.0, 0.3, 1.0);

  fancy_cairo_stroke_preserve (cr);

  draw_twisted (cr,
		-20, -150,
		"Serif 60",
		"WOW!");
}

int main (int argc, char **argv)
{
  cairo_t *cr;
  char *filename;
  cairo_status_t status;
  cairo_surface_t *surface;

  if (argc != 2)
    {
      g_printerr ("Usage: cairotwisted OUTPUT_FILENAME\n");
      return 1;
    }

  filename = argv[1];

  surface = cairo_image_surface_create (CAIRO_FORMAT_ARGB32,
					1000, 800);
  cr = cairo_create (surface);

  cairo_set_source_rgb (cr, 1.0, 1.0, 1.0);
  cairo_paint (cr);

  draw_dream (cr);
  draw_wow (cr);

  cairo_destroy (cr);

  status = cairo_surface_write_to_png (surface, filename);
  cairo_surface_destroy (surface);

  if (status != CAIRO_STATUS_SUCCESS)
    {
      g_printerr ("Could not save png to '%s'\n", filename);
      return 1;
    }

  return 0;
}