/* Returns the length of path. path must be flattened
* (i.e. only consist of line segments)
*/
static double _rsvg_path_length(cairo_path_t *path) {
int i;
double distance = 0.0;
cairo_path_data_t *last_point, *cur_point, *last_move_to;
for (i=0; i < path->num_data; i += path->data[i].header.length) {
cairo_path_data_t *data = &path->data[i];
switch (data->header.type) {
case CAIRO_PATH_MOVE_TO:
last_move_to = data;
last_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;
// fall through
case CAIRO_PATH_LINE_TO:
cur_point = &data[1];
distance += two_points_distance(last_point, cur_point);
last_point = cur_point;
break;
default:
g_assert_not_reached ();
}
}
return distance;
}
/* 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_image_surface_create(CAIRO_FORMAT_A8, 0, 0);
cairo_t* cr = cairo_create(surface);
double length = 0;
cairo_path_t* path;
cairo_path_data_t* data;
cairo_path_data_t current_point;
int i;
current_point.point.x = 0.0;
current_point.point.y = 0.0;
cairo_surface_destroy(surface);
cairo_move_to(cr, x0, y0);
cairo_curve_to(cr, x1, y1, x2, y2, x3, y3);
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(¤t_point, &data[1]);
current_point = data[1];
break;
default:
break;
}
}
cairo_path_destroy(path);
cairo_destroy(cr);
return length;
}
/* Compute parametrization info. That is, for each part of the cairo path, tags it with
* its length. */
static parametrization_t* parametrize_path(cairo_path_t* path) {
parametrization_t* parametrization = 0;
cairo_path_data_t* data = 0;
cairo_path_data_t last_move_to;
cairo_path_data_t current_point;
int i;
current_point.point.x = 0.0;
current_point.point.y = 0.0;
parametrization = (parametrization_t*)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;
case CAIRO_PATH_LINE_TO:
parametrization[i] = two_points_distance(¤t_point, &data[1]);
current_point = data[1];
break;
case CAIRO_PATH_CURVE_TO:
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;
}
}
return parametrization;
}
/* 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 (¤t_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 (¤t_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;
}
/* Returns the x, y, and tangent vector angle of a point distance
* d down a path. path must be flattened.
*/
static void _rsvg_path_point_on_path(cairo_path_t *path, double d,
double *x, double *y, double *theta)
{
int i;
double dist_so_far = 0.0;
cairo_path_data_t *last_point, *cur_point, *last_move_to;
for (i=0; i < path->num_data; i += path->data[i].header.length) {
cairo_path_data_t *data = &path->data[i];
switch (data->header.type) {
case CAIRO_PATH_MOVE_TO:
last_move_to = data;
last_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;
// fall through
case CAIRO_PATH_LINE_TO:
cur_point = &data[1];
dist_so_far += two_points_distance(last_point, cur_point);
// Reached distance d along the path
if (dist_so_far > d) {
double dlength = dist_so_far - d;
double angle = atan2(cur_point->point.y - last_point->point.y,
cur_point->point.x - last_point->point.x);
*x = dlength * cos(angle) + last_point->point.x;
*y = dlength * sin(angle) + last_point->point.y;
// Find the normal vector and normalize to [-pi,pi]
angle -= G_PI/2.0;
if (angle < -G_PI)
angle += 2*G_PI;
*theta = angle;
} else {
last_point = cur_point;
}
break;
default:
g_assert_not_reached ();
}
}
}