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curve: Handle degenerate cases

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Nothing prevents control points from being identical,
and if that happens, some of our constructions involving
tangents and normals break down. Handle these cases in
get_{start,end}_tangent and offset, for the case of
cubics.
This commit is contained in:
Matthias Clasen
2020-12-19 22:14:26 -05:00
parent 0bef169b32
commit ad145e201b
1 changed files with 99 additions and 16 deletions
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115
gsk/gskcurve.c
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@@ -558,7 +558,15 @@ gsk_curve_curve_get_start_tangent (const GskCurve *curve,
{
const GskCurveCurve *self = &curve->curve;
get_tangent (&self->points[0], &self->points[1], tangent);
if (graphene_point_near (&self->points[0], &self->points[1], 0.0001))
{
if (graphene_point_near (&self->points[0], &self->points[2], 0.0001))
get_tangent (&self->points[0], &self->points[3], tangent);
else
get_tangent (&self->points[0], &self->points[2], tangent);
}
else
get_tangent (&self->points[0], &self->points[1], tangent);
}
static void
@@ -567,7 +575,15 @@ gsk_curve_curve_get_end_tangent (const GskCurve *curve,
{
const GskCurveCurve *self = &curve->curve;
get_tangent (&self->points[2], &self->points[3], tangent);
if (graphene_point_near (&self->points[2], &self->points[3], 0.0001))
{
if (graphene_point_near (&self->points[1], &self->points[3], 0.0001))
get_tangent (&self->points[0], &self->points[3], tangent);
else
get_tangent (&self->points[1], &self->points[3], tangent);
}
else
get_tangent (&self->points[2], &self->points[3], tangent);
}
static void
@@ -667,25 +683,92 @@ gsk_curve_curve_offset (const GskCurve *curve,
graphene_vec2_t n;
graphene_point_t p[4];
graphene_point_t m1, m2, m3, m4;
int coinc;
/* 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);
coinc = (graphene_point_near (&pts[0], &pts[1], 0.001) << 0) |
(graphene_point_near (&pts[1], &pts[2], 0.001) << 1) |
(graphene_point_near (&pts[2], &pts[3], 0.001) << 2);
get_normal (&pts[1], &pts[2], &n);
scale_point (&pts[1], &n, distance, &m2);
scale_point (&pts[2], &n, distance, &m3);
if (coinc == 7)
{
/* just give up */
p[0] = pts[0];
p[1] = pts[1];
p[2] = pts[2];
p[3] = pts[3];
}
else if (coinc == 3 || coinc == 5 || coinc == 6)
{
/* a straight line */
get_normal (&pts[0], &pts[3], &n);
scale_point (&pts[0], &n, distance, &p[0]);
scale_point (&pts[3], &n, distance, &p[3]);
get_normal (&pts[2], &pts[3], &n);
scale_point (&pts[2], &n, distance, &m4);
scale_point (&pts[3], &n, distance, &p[3]);
if (coinc & (1 << 0))
p[1] = p[0];
else
p[1] = p[3];
if (coinc & (1 << 2))
p[2] = p[3];
else
p[2] = p[0];
}
else if (coinc == 1 || coinc == 2 || coinc == 4)
{
graphene_point_t p1;
if (!line_intersection (&p[0], &m1, &m2, &m3, &p[1]))
p[1] = m1;
if (coinc == 1)
p1 = pts[2];
else
p1 = pts[1];
if (!line_intersection (&m2, &m3, &m4, &p[3], &p[2]))
p[2] = m4;
get_normal (&pts[0], &p1, &n);
scale_point (&pts[0], &n, distance, &p[0]);
scale_point (&p1, &n, distance, &m1);
get_normal (&p1, &pts[3], &n);
scale_point (&p1, &n, distance, &m2);
scale_point (&pts[3], &n, distance, &p[3]);
if (!line_intersection (&p[0], &m1, &m2, &p[3], &m3))
m3 = m1;
if (coinc == 1)
{
p[1] = p[0];
p[2] = m3;
}
else if (coinc == 2)
{
p[1] = m3;
p[2] = m3;
}
else
{
p[1] = m3;
p[2] = p[3];
}
}
else if (coinc == 0)
{
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_curve_curve_init_from_points (&offset->curve, p);
}