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rewrote the line segment intersection function to make the static analyzer happy (#12902)

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* rewrote the line segment intersection function to make the static analyzer happy

* fixed bug with improper "no intersection" detection in some of corner cases

* fixed bug with improper "no intersection" detection in some of corner cases
This commit is contained in:
Vadim Pisarevsky 2018-10-23 17:09:23 +03:00 committed by GitHub
parent 9c23f2f1a6
commit ea31c09384
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GPG Key ID: 4AEE18F83AFDEB23
1 changed files with 28 additions and 47 deletions
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75
modules/imgproc/src/geometry.cpp
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@ -295,11 +295,19 @@ static bool between( Point2f a, Point2f b, Point2f c )
((a.y >= c.y) && (c.y >= b.y));
}
static char parallelInt( Point2f a, Point2f b, Point2f c, Point2f d, Point2f& p, Point2f& q )
enum LineSegmentIntersection
{
char code = 'e';
LS_NO_INTERSECTION = 0,
LS_SINGLE_INTERSECTION = 1,
LS_OVERLAP = 2,
LS_ENDPOINT_INTERSECTION = 3
};
static LineSegmentIntersection parallelInt( Point2f a, Point2f b, Point2f c, Point2f d, Point2f& p, Point2f& q )
{
LineSegmentIntersection code = LS_OVERLAP;
if( areaSign(a, b, c) != 0 )
code = '0';
code = LS_NO_INTERSECTION;
else if( between(a, b, c) && between(a, b, d))
p = c, q = d;
else if( between(c, d, a) && between(c, d, b))
@ -313,60 +321,33 @@ static char parallelInt( Point2f a, Point2f b, Point2f c, Point2f d, Point2f& p,
else if( between(a, b, d) && between(c, d, a))
p = d, q = a;
else
code = '0';
code = LS_NO_INTERSECTION;
return code;
}
//---------------------------------------------------------------------
// segSegInt: Finds the point of intersection p between two closed
// segments ab and cd. Returns p and a char with the following meaning:
// 'e': The segments collinearly overlap, sharing a point.
// 'v': An endpoint (vertex) of one segment is on the other segment,
// but 'e' doesn't hold.
// '1': The segments intersect properly (i.e., they share a point and
// neither 'v' nor 'e' holds).
// '0': The segments do not intersect (i.e., they share no points).
// Note that two collinear segments that share just one point, an endpoint
// of each, returns 'e' rather than 'v' as one might expect.
//---------------------------------------------------------------------
static char segSegInt( Point2f a, Point2f b, Point2f c, Point2f d, Point2f& p, Point2f& q )
// Finds intersection of two line segments: (a, b) and (c, d).
static LineSegmentIntersection intersectLineSegments( Point2f a, Point2f b, Point2f c,
Point2f d, Point2f& p, Point2f& q )
{
double s, t; // The two parameters of the parametric eqns.
double num, denom; // Numerator and denoninator of equations.
char code = '?'; // Return char characterizing intersection.
denom = a.x * (double)( d.y - c.y ) +
b.x * (double)( c.y - d.y ) +
d.x * (double)( b.y - a.y ) +
c.x * (double)( a.y - b.y );
double denom = a.x * (double)(d.y - c.y) + b.x * (double)(c.y - d.y) +
d.x * (double)(b.y - a.y) + c.x * (double)(a.y - b.y);
// If denom is zero, then segments are parallel: handle separately.
if (denom == 0.0)
if( denom == 0. )
return parallelInt(a, b, c, d, p, q);
num = a.x * (double)( d.y - c.y ) +
c.x * (double)( a.y - d.y ) +
d.x * (double)( c.y - a.y );
if ( (num == 0.0) || (num == denom) ) code = 'v';
s = num / denom;
double num = a.x * (double)(d.y - c.y) + c.x * (double)(a.y - d.y) + d.x * (double)(c.y - a.y);
double s = num / denom;
num = -( a.x * (double)( c.y - b.y ) +
b.x * (double)( a.y - c.y ) +
c.x * (double)( b.y - a.y ) );
if ( (num == 0.0) || (num == denom) ) code = 'v';
t = num / denom;
if ( (0.0 < s) && (s < 1.0) &&
(0.0 < t) && (t < 1.0) )
code = '1';
else if ( (0.0 > s) || (s > 1.0) ||
(0.0 > t) || (t > 1.0) )
code = '0';
num = a.x * (double)(b.y - c.y) + b.x * (double)(c.y - a.y) + c.x * (double)(a.y - b.y);
double t = num / denom;
p.x = (float)(a.x + s*(b.x - a.x));
p.y = (float)(a.y + s*(b.y - a.y));
q = p;
return code;
return s < 0. || s > 1. || t < 0. || t > 1. ? LS_NO_INTERSECTION :
s == 0. || s == 1. || t == 0. || t == 1. ? LS_ENDPOINT_INTERSECTION : LS_SINGLE_INTERSECTION;
}
static tInFlag inOut( Point2f p, tInFlag inflag, int aHB, int bHA, Point2f*& result )
@ -424,8 +405,8 @@ static int intersectConvexConvex_( const Point2f* P, int n, const Point2f* Q, in
// If A & B intersect, update inflag.
Point2f p, q;
int code = segSegInt( P[a1], P[a], Q[b1], Q[b], p, q );
if( code == '1' || code == 'v' )
LineSegmentIntersection code = intersectLineSegments( P[a1], P[a], Q[b1], Q[b], p, q );
if( code == LS_SINGLE_INTERSECTION || code == LS_ENDPOINT_INTERSECTION )
{
if( inflag == Unknown && FirstPoint )
{
@ -440,7 +421,7 @@ static int intersectConvexConvex_( const Point2f* P, int n, const Point2f* Q, in
//-----Advance rules-----
// Special case: A & B overlap and oppositely oriented.
if( code == 'e' && A.ddot(B) < 0 )
if( code == LS_OVERLAP && A.ddot(B) < 0 )
{
addSharedSeg( p, q, result );
return (int)(result - result0);