Lerking/gtk
1
0
Fork 0
Code Issues Pull Requests Actions Packages Projects Releases Wiki Activity

curve: Add gsk_curve_offset

Browse Source 
This method creates an offset curve from an existing
curve by just moving the control points laterally.

This will be used in stroking.
This commit is contained in:
Matthias Clasen
2023-06-29 23:09:35 -04:00
parent e5c97cc7fb
commit c020eeac70
2 changed files with 176 additions and 0 deletions
Download Patch File Download Diff File Expand all files Collapse all files

173
gsk/gskcurve.c
View File

@@ -74,6 +74,9 @@ struct _GskCurveClass
GskBoundingBox *bounds);
void (* get_tight_bounds) (const GskCurve *curve,
GskBoundingBox *bounds);
void (* offset) (const GskCurve *curve,
float distance,
GskCurve *offset_curve);
};
/* {{{ Utilities */
@@ -87,6 +90,26 @@ get_tangent (const graphene_point_t *p0,
graphene_vec2_normalize (t, t);
}
static void
get_normal (const graphene_point_t *p0,
const graphene_point_t *p1,
graphene_vec2_t *n)
{
graphene_vec2_init (n, p0->y - p1->y, p1->x - p0->x);
graphene_vec2_normalize (n, n);
}
/* Compute q = p + d * n */
static void
scale_point (const graphene_point_t *p,
const graphene_vec2_t *n,
float d,
graphene_point_t *q)
{
q->x = p->x + d * graphene_vec2_get_x (n);
q->y = p->y + d * graphene_vec2_get_y (n);
}
/* Replace a line by an equivalent quad,
* and a quad by an equivalent cubic.
*/
@@ -129,6 +152,40 @@ gsk_curve_elevate (const GskCurve *curve,
/* }}} */
/* {{{ Line */
/* Set p to the intersection of the lines through a, b and c, d.
* Return the number of intersections found (0 or 1)
*/
static int
line_intersection (const graphene_point_t *a,
const graphene_point_t *b,
const graphene_point_t *c,
const graphene_point_t *d,
graphene_point_t *p)
{
float a1 = b->y - a->y;
float b1 = a->x - b->x;
float c1 = a1*a->x + b1*a->y;
float a2 = d->y - c->y;
float b2 = c->x - d->x;
float c2 = a2*c->x+ b2*c->y;
float det = a1*b2 - a2*b1;
if (fabs (det) < 0.001)
{
p->x = NAN;
p->y = NAN;
return 0;
}
else
{
p->x = (b2*c1 - b1*c2) / det;
p->y = (a1*c2 - a2*c1) / det;
return 1;
}
}
static void
gsk_line_curve_init_from_points (GskLineCurve *self,
GskPathOperation op,
@@ -310,6 +367,23 @@ gsk_line_curve_get_bounds (const GskCurve *curve,
gsk_bounding_box_init (bounds, &pts[0], &pts[1]);
}
static void
gsk_line_curve_offset (const GskCurve *curve,
float distance,
GskCurve *offset_curve)
{
const GskLineCurve *self = &curve->line;
const graphene_point_t *pts = self->points;
graphene_vec2_t n;
graphene_point_t p[4];
get_normal (&pts[0], &pts[1], &n);
scale_point (&pts[0], &n, distance, &p[0]);
scale_point (&pts[1], &n, distance, &p[1]);
gsk_curve_init (offset_curve, gsk_pathop_encode (GSK_PATH_LINE, p));
}
static const GskCurveClass GSK_LINE_CURVE_CLASS = {
gsk_line_curve_init,
gsk_line_curve_init_foreach,
@@ -329,6 +403,7 @@ static const GskCurveClass GSK_LINE_CURVE_CLASS = {
gsk_line_curve_decompose_curve,
gsk_line_curve_get_bounds,
gsk_line_curve_get_bounds,
gsk_line_curve_offset,
};
/* }}} */
@@ -677,6 +752,32 @@ gsk_quad_curve_get_tight_bounds (const GskCurve *curve,
}
}
static void
gsk_quad_curve_offset (const GskCurve *curve,
float distance,
GskCurve *offset)
{
const GskCubicCurve *self = &curve->cubic;
const graphene_point_t *pts = self->points;
graphene_vec2_t n;
graphene_point_t p[4];
graphene_point_t m1, m2;
/* Simply scale control points, a la Tiller and Hanson */
get_normal (&pts[0], &pts[1], &n);
scale_point (&pts[0], &n, distance, &p[0]);
scale_point (&pts[1], &n, distance, &m1);
get_normal (&pts[1], &pts[2], &n);
scale_point (&pts[1], &n, distance, &m2);
scale_point (&pts[2], &n, distance, &p[2]);
if (!line_intersection (&p[0], &m1, &m2, &p[2], &p[1]))
gsk_curve_get_point (curve, 0.5, &p[1]);
gsk_quad_curve_init_from_points (&offset->quad, p);
}
static const GskCurveClass GSK_QUAD_CURVE_CLASS = {
gsk_quad_curve_init,
gsk_quad_curve_init_foreach,
@@ -696,6 +797,7 @@ static const GskCurveClass GSK_QUAD_CURVE_CLASS = {
gsk_quad_curve_decompose_curve,
gsk_quad_curve_get_bounds,
gsk_quad_curve_get_tight_bounds,
gsk_quad_curve_offset,
};
/* }}} */
@@ -1159,6 +1261,39 @@ gsk_cubic_curve_get_tight_bounds (const GskCurve *curve,
}
}
static void
gsk_cubic_curve_offset (const GskCurve *curve,
float distance,
GskCurve *offset)
{
const GskCubicCurve *self = &curve->cubic;
const graphene_point_t *pts = self->points;
graphene_vec2_t n;
graphene_point_t p[4];
graphene_point_t m1, m2, m3, m4;
/* Simply scale control points, a la Tiller and Hanson */
get_normal (&pts[0], &pts[1], &n);
scale_point (&pts[0], &n, distance, &p[0]);
scale_point (&pts[1], &n, distance, &m1);
get_normal (&pts[1], &pts[2], &n);
scale_point (&pts[1], &n, distance, &m2);
scale_point (&pts[2], &n, distance, &m3);
get_normal (&pts[2], &pts[3], &n);
scale_point (&pts[2], &n, distance, &m4);
scale_point (&pts[3], &n, distance, &p[3]);
if (!line_intersection (&p[0], &m1, &m2, &m3, &p[1]))
p[1] = m1;
if (!line_intersection (&m2, &m3, &m4, &p[3], &p[2]))
p[2] = m4;
gsk_cubic_curve_init_from_points (&offset->cubic, p);
}
static const GskCurveClass GSK_CUBIC_CURVE_CLASS = {
gsk_cubic_curve_init,
gsk_cubic_curve_init_foreach,
@@ -1178,6 +1313,7 @@ static const GskCurveClass GSK_CUBIC_CURVE_CLASS = {
gsk_cubic_curve_decompose_curve,
gsk_cubic_curve_get_bounds,
gsk_cubic_curve_get_tight_bounds,
gsk_cubic_curve_offset,
};
/* }}} */
@@ -1818,6 +1954,34 @@ gsk_conic_curve_get_tight_bounds (const GskCurve *curve,
}
}
static void
gsk_conic_curve_offset (const GskCurve *curve,
float distance,
GskCurve *offset)
{
const GskConicCurve *self = &curve->conic;
const graphene_point_t *pts = self->points;
graphene_vec2_t n;
graphene_point_t p[4];
graphene_point_t m1, m2;
/* Simply scale control points, a la Tiller and Hanson */
get_normal (&pts[0], &pts[1], &n);
scale_point (&pts[0], &n, distance, &p[0]);
scale_point (&pts[1], &n, distance, &m1);
get_normal (&pts[1], &pts[3], &n);
scale_point (&pts[1], &n, distance, &m2);
scale_point (&pts[3], &n, distance, &p[3]);
if (!line_intersection (&p[0], &m1, &m2, &p[3], &p[1]))
p[1] = m1;
p[2] = pts[2];
gsk_conic_curve_init_from_points (&offset->conic, p);
}
static const GskCurveClass GSK_CONIC_CURVE_CLASS = {
gsk_conic_curve_init,
gsk_conic_curve_init_foreach,
@@ -1837,6 +2001,7 @@ static const GskCurveClass GSK_CONIC_CURVE_CLASS = {
gsk_conic_curve_decompose_curve,
gsk_conic_curve_get_bounds,
gsk_conic_curve_get_tight_bounds,
gsk_conic_curve_offset,
};
/* }}} */
@@ -2029,6 +2194,14 @@ gsk_curve_get_tight_bounds (const GskCurve *curve,
get_class (curve->op)->get_tight_bounds (curve, bounds);
}
void
gsk_curve_offset (const GskCurve *curve,
float distance,
GskCurve *offset_curve)
{
get_class (curve->op)->offset (curve, distance, offset_curve);
}
/* }}} */
/* vim:set foldmethod=marker expandtab: */

3
gsk/gskcurveprivate.h
View File

@@ -163,6 +163,9 @@ void gsk_curve_get_bounds (const GskCurve
GskBoundingBox *bounds);
void gsk_curve_get_tight_bounds (const GskCurve *curve,
GskBoundingBox *bounds);
void gsk_curve_offset (const GskCurve *curve,
float distance,
GskCurve *offset_curve);
int gsk_curve_get_curvature_points (const GskCurve *curve,
float t[3]);