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Corrected math for offsets to work also for angles different from 90 degrees.

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- cameo/path.c (offset_point): calculation assumed the normals were
  linearly independent. Replaced it with corrected version.
This commit is contained in:
Werner Almesberger 2010-11-01 16:42:32 -03:00
parent 54d8549fa2
commit 5c9e7d5e52
1 changed files with 11 additions and 2 deletions
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13
cameo/path.c
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@ -104,6 +104,7 @@ static struct point *offset_point(const struct point *a, const struct point *b,
double ax, ay, bx, by;
double aa, bb;
double nx, ny;
double angle, f;
struct point *p;
ax = b->x-a->x;
@ -113,6 +114,7 @@ static struct point *offset_point(const struct point *a, const struct point *b,
aa = hypot(ax, ay);
bb = hypot(bx, by);
if (left) {
nx = -(ay/aa+by/bb);
ny = ax/aa+bx/bb;
@ -121,8 +123,15 @@ static struct point *offset_point(const struct point *a, const struct point *b,
ny = -(ax/aa+bx/bb);
}
nx *= off;
ny *= off;
/* angle between AB and BC */
angle = acos(-(ax*bx+ay*by)/aa/bb);
/* multiplier for combination of normal vectors */
f = off/sin(angle/2);
f /= hypot(nx, ny);
nx *= f;
ny *= f;
p = alloc_type(struct point);
p->x = b->x+nx;