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curve: Refine line-line intersection

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For collinear line segments, return up to 2 intersections
for the endpoints of the intersection (which is also a
line segment in this case).

Tests included.
This commit is contained in:
Matthias Clasen
2022-03-28 00:18:58 -04:00
parent 6aa38e6b39
commit ab8a32bc76
2 changed files with 168 additions and 7 deletions
Download Patch File Download Diff File Expand all files Collapse all files

107
gsk/gskcurveintersect.c
View File

@@ -33,7 +33,8 @@ line_intersect (const GskCurve *curve1,
const GskCurve *curve2,
float *t1,
float *t2,
graphene_point_t *p)
graphene_point_t *p,
int n)
{
const graphene_point_t *pts1 = curve1->line.points;
const graphene_point_t *pts2 = curve2->line.points;
@@ -43,22 +44,114 @@ line_intersect (const GskCurve *curve1,
float b2 = pts2[0].y - pts2[1].y;
float det = a1 * b2 - b1 * a2;
if (det != 0)
if (fabs(det) > 0.01)
{
float tt = ((pts1[0].x - pts2[0].x) * b2 - (pts1[0].y - pts2[0].y) * a2) / det;
float ss = - ((pts1[0].y - pts2[0].y) * a1 - (pts1[0].x - pts2[0].x) * b1) / det;
if (acceptable (tt) && acceptable (ss))
{
p->x = pts1[0].x + tt * (pts1[1].x - pts1[0].x);
p->y = pts1[0].y + tt * (pts1[1].y - pts1[0].y);
p[0].x = pts1[0].x + tt * (pts1[1].x - pts1[0].x);
p[0].y = pts1[0].y + tt * (pts1[1].y - pts1[0].y);
*t1 = tt;
*t2 = ss;
t1[0] = tt;
t2[0] = ss;
return 1;
}
}
else /* parallel lines */
{
float r = a1 * (pts1[1].y - pts2[0].y) - (pts1[1].x - pts2[0].x) * b1;
float dist = (r * r) / (a1 * a1 + b1 * b1);
float t, s, tt, ss;
if (dist > 0.01)
return 0;
if (pts1[1].x != pts1[0].x)
{
t = (pts2[0].x - pts1[0].x) / (pts1[1].x - pts1[0].x);
s = (pts2[1].x - pts1[0].x) / (pts1[1].x - pts1[0].x);
}
else
{
t = (pts2[0].y - pts1[0].y) / (pts1[1].y - pts1[0].y);
s = (pts2[1].y - pts1[0].y) / (pts1[1].y - pts1[0].y);
}
if ((t < 0 && s < 0) || (t > 1 && s > 1))
return 0;
if (acceptable (t))
{
t1[0] = t;
t2[0] = 0;
p[0] = pts2[0];
}
else if (t < 0)
{
if (pts2[1].x != pts2[0].x)
tt = (pts1[0].x - pts2[0].x) / (pts2[1].x - pts2[0].x);
else
tt = (pts1[0].y - pts2[0].y) / (pts2[1].y - pts2[0].y);
t1[0] = 0;
t2[0] = tt;
p[0] = pts1[0];
}
else
{
if (pts2[1].x != pts2[0].x)
tt = (pts1[1].x - pts2[0].x) / (pts2[1].x - pts2[0].x);
else
tt = (pts1[1].y - pts2[0].y) / (pts2[1].y - pts2[0].y);
t1[0] = 1;
t2[0] = tt;
p[0] = pts1[1];
}
if (acceptable (s))
{
if (t2[0] == 1)
return 1;
t1[1] = s;
t2[1] = 1;
p[1] = pts2[1];
}
else if (s < 0)
{
if (t1[0] == 0)
return 1;
if (pts2[1].x != pts2[0].x)
ss = (pts1[0].x - pts2[0].x) / (pts2[1].x - pts2[0].x);
else
ss = (pts1[0].y - pts2[0].y) / (pts2[1].y - pts2[0].y);
t1[1] = 0;
t2[1] = ss;
p[1] = pts1[0];
}
else
{
if (t1[0] == 1)
return 1;
if (pts2[1].x != pts2[0].x)
ss = (pts1[1].x - pts2[0].x) / (pts2[1].x - pts2[0].x);
else
ss = (pts1[1].y - pts2[0].y) / (pts2[1].y - pts2[0].y);
t1[1] = 1;
t2[1] = ss;
p[1] = pts1[1];
}
return 2;
}
return 0;
}
@@ -451,7 +544,7 @@ gsk_curve_intersect (const GskCurve *curve1,
* Everything else is done via bisection.
*/
if (op1 == GSK_PATH_LINE && op2 == GSK_PATH_LINE)
return line_intersect (curve1, curve2, t1, t2, p);
return line_intersect (curve1, curve2, t1, t2, p, n);
else if (op1 == GSK_PATH_LINE && op2 == GSK_PATH_CURVE)
return line_curve_intersect (curve1, curve2, t1, t2, p, n);
else if (op1 == GSK_PATH_CURVE && op2 == GSK_PATH_LINE)

68
testsuite/gsk/curve-special-cases.c
View File

@@ -223,6 +223,73 @@ test_errant_intersection2 (void)
g_assert_true (n == 1);
}
static void
test_line_intersection_parallel (void)
{
GskCurve l1;
GskCurve l2;
graphene_point_t p1[1];
graphene_point_t p2[2];
float t1[3], t2[3];
graphene_point_t s[3];
int n;
graphene_point_init (&p1[0], 0, 100);
graphene_point_init (&p1[1], 100, 100);
gsk_curve_init (&l1, gsk_pathop_encode (GSK_PATH_LINE, p1));
graphene_point_init (&p2[0], 0, 110);
graphene_point_init (&p2[1], 100, 110);
gsk_curve_init (&l2, gsk_pathop_encode (GSK_PATH_LINE, p2));
n = gsk_curve_intersect (&l1, &l2, t1, t2, s, G_N_ELEMENTS (s));
g_assert_true (n == 0);
graphene_point_init (&p2[0], 110, 100);
graphene_point_init (&p2[1], 210, 100);
gsk_curve_init (&l2, gsk_pathop_encode (GSK_PATH_LINE, p2));
n = gsk_curve_intersect (&l1, &l2, t1, t2, s, G_N_ELEMENTS (s));
g_assert_true (n == 0);
graphene_point_init (&p2[0], 0, 100);
graphene_point_init (&p2[1], -100, 100);
gsk_curve_init (&l2, gsk_pathop_encode (GSK_PATH_LINE, p2));
n = gsk_curve_intersect (&l1, &l2, t1, t2, s, G_N_ELEMENTS (s));
g_assert_true (n == 1);
g_assert_cmpfloat_with_epsilon (t1[0], 0, 0.001);
g_assert_cmpfloat_with_epsilon (t2[0], 0, 0.001);
graphene_point_init (&p2[0], 20, 100);
graphene_point_init (&p2[1], 80, 100);
gsk_curve_init (&l2, gsk_pathop_encode (GSK_PATH_LINE, p2));
n = gsk_curve_intersect (&l1, &l2, t1, t2, s, G_N_ELEMENTS (s));
g_assert_true (n == 2);
g_assert_cmpfloat_with_epsilon (t1[0], 0.2, 0.001);
g_assert_cmpfloat_with_epsilon (t1[1], 0.8, 0.001);
g_assert_cmpfloat_with_epsilon (t2[0], 0, 0.001);
g_assert_cmpfloat_with_epsilon (t2[1], 1, 0.001);
graphene_point_init (&p2[0], 150, 100);
graphene_point_init (&p2[1], 50, 100);
gsk_curve_init (&l2, gsk_pathop_encode (GSK_PATH_LINE, p2));
n = gsk_curve_intersect (&l1, &l2, t1, t2, s, G_N_ELEMENTS (s));
g_assert_true (n == 2);
g_assert_cmpfloat_with_epsilon (t1[0], 1, 0.001);
g_assert_cmpfloat_with_epsilon (t1[1], 0.5, 0.001);
g_assert_cmpfloat_with_epsilon (t2[0], 0.5, 0.001);
g_assert_cmpfloat_with_epsilon (t2[1], 1, 0.001);
}
int
main (int argc,
char *argv[])
@@ -234,6 +301,7 @@ main (int argc,
g_test_add_func ("/curve/special/degenerate-tangents", test_curve_degenerate_tangents);
g_test_add_func ("/curve/errant-intersection", test_errant_intersection);
g_test_add_func ("/curve/errant-intersection2", test_errant_intersection2);
g_test_add_func ("/curve/line-intersection-parallel", test_line_intersection_parallel);
return g_test_run ();
}