Slic3r::Arachne::LinearAlg2D Namespace Reference

Functions
static int64_t	pointIsLeftOfLine (const Point &p, const Point &a, const Point &b)
static float	getAngleLeft (const Point &a, const Point &b, const Point &c)

Function Documentation

getAngleLeft()

float Slic3r::Arachne::LinearAlg2D::getAngleLeft ( const Point & a, const Point & b, const Point & c )

inlinestatic

Compute the angle between two consecutive line segments.

The angle is computed from the left side of b when looking from a.

c \ . \ b angle| | a

Parameters

a	start of first line segment
b	end of first segment and start of second line segment
c	end of second line segment

Returns

the angle in radians between 0 and 2 * pi of the corner in b

{
    const Vec2i64 ba   = (a - b).cast<int64_t>();
    const Vec2i64 bc   = (c - b).cast<int64_t>();
    const int64_t dott = ba.dot(bc);      // dot product
    const int64_t det  = cross2(ba, bc); // determinant
    if (det == 0) {
        if ((ba.x() != 0 && (ba.x() > 0) == (bc.x() > 0)) || (ba.x() == 0 && (ba.y() > 0) == (bc.y() > 0)))
            return 0; // pointy bit
        else
            return float(M_PI); // straight bit
    }
    const float angle = -atan2(double(det), double(dott)); // from -pi to pi
    if (angle >= 0)
        return angle;
    else
        return M_PI * 2 + angle;
}

References Slic3r::angle(), Slic3r::cast(), Slic3r::cross2(), and M_PI.

Referenced by Slic3r::Arachne::removeColinearEdges().

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pointIsLeftOfLine()

int64_t Slic3r::Arachne::LinearAlg2D::pointIsLeftOfLine ( const Point & p, const Point & a, const Point & b )

inlinestatic

Returns the determinant of the 2D matrix defined by the vectors ab and ap as rows.

The returned value is zero for p lying (approximately) on the line going through a and b The value is positive for values lying to the left and negative for values lying to the right when looking from a to b.

Parameters

p	the point to check
a	the from point of the line
b	the to point of the line

Returns

a positive value when p lies to the left of the line from a to b

{
    return int64_t(b.x() - a.x()) * int64_t(p.y() - a.y()) - int64_t(b.y() - a.y()) * int64_t(p.x() - a.x());
}

Referenced by Slic3r::Arachne::fixSelfIntersections().

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