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Optimize edges_intersect().

Browse source 
I found wolfram's line-line intersection page and noticed their equation
for the time of intersection was rather different to mine. After analyzing
the differences, it turns out they produce exactly the same results (when
the lines are coplanar), but their method allows me to eliminate one dot
product (4->3). Not only that, but it turns out that their method works
equally well for skew lines (ie, non-coplanar).

mine:
  CxA.CxA
  -------
  CxA.AxB

theirs:
  CxA.AxB
  -------
  AxB.AxB
This commit is contained in:
Bill Currie 2011-12-07 10:35:58 +09:00
parent ff693a956a
commit 4f13d19b7e
1 changed files with 5 additions and 6 deletions
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11
libs/models/trace.c
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@ -127,7 +127,7 @@ edges_intersect (const vec3_t p1, const vec3_t p2,
{
vec3_t p, r, b;
vec3_t p_r, b_p, b_r;
vec_t tp, tpd, tr, trd;
vec_t tp, tr, den;
VectorSubtract (p2, p1, p);
VectorSubtract (r2, r1, r);
@ -137,11 +137,10 @@ edges_intersect (const vec3_t p1, const vec3_t p2,
return false;
CrossProduct (b, p, b_p);
CrossProduct (b, r, b_r);
tr = DotProduct (b_p, b_p);
trd = DotProduct (b_p, p_r);
tp = DotProduct (b_r, b_r);
tpd = DotProduct (b_r, p_r);
if ((tr < 0 || tr > trd) || (tp < 0 || tp > tpd))
tr = DotProduct (b_p, p_r);
tp = DotProduct (b_r, p_r);
den = DotProduct (p_r, p_r);
if ((tr < 0 || tr > den) || (tp < 0 || tp > den))
return false;
return true;
}