lw_arc_angle()

static double lw_arc_angle ( const POINT2D *  a, const POINT2D *  b, const POINT2D *  c  )

static

Return ABC angle in radians TODO: move to lwalgorithm.

Definition at line 777 of file lwstroke.c.

References POINT2D::x, and POINT2D::y.

Referenced by pt_continues_arc(), and pta_unstroke().

{
  POINT2D ab, cb;

  ab.x = b->x - a->x;
  ab.y = b->y - a->y;

  cb.x = b->x - c->x;
  cb.y = b->y - c->y;

  double dot = (ab.x * cb.x + ab.y * cb.y); /* dot product */
  double cross = (ab.x * cb.y - ab.y * cb.x); /* cross product */

  double alpha = atan2(cross, dot);

  return alpha;
}

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