C++ SkVector::lengthSqd方法代码示例

SkScalar SkPoint::distanceToLineSegmentBetweenSqd(const SkPoint& a,
                                                  const SkPoint& b) const {
    // See comments to distanceToLineBetweenSqd. If the projection of c onto
    // u is between a and b then this returns the same result as that
    // function. Otherwise, it returns the distance to the closer of a and
    // b. Let the projection of v onto u be v'.  There are three cases:
    //    1. v' points opposite to u. c is not between a and b and is closer
    //       to a than b.
    //    2. v' points along u and has magnitude less than y. c is between
    //       a and b and the distance to the segment is the same as distance
    //       to the line ab.
    //    3. v' points along u and has greater magnitude than u. c is not
    //       not between a and b and is closer to b than a.
    // v' = (u dot v) * u / |u|. So if (u dot v)/|u| is less than zero we're
    // in case 1. If (u dot v)/|u| is > |u| we are in case 3. Otherwise
    // we're in case 2. We actually compare (u dot v) to 0 and |u|^2 to
    // avoid a sqrt to compute |u|.

    SkVector u = b - a;
    SkVector v = *this - a;

    SkScalar uLengthSqd = u.lengthSqd();
    SkScalar uDotV = SkPoint::DotProduct(u, v);

    if (uDotV <= 0) {
        return v.lengthSqd();
    } else if (uDotV > uLengthSqd) {
        return b.distanceToSqd(*this);
    } else {
        SkScalar det = u.cross(v);
        return SkScalarMulDiv(det, det, uLengthSqd);
    }
}

// Offset line segment p0-p1 'd0' and 'd1' units in the direction specified by 'side'
bool SkOffsetSegment(const SkPoint& p0, const SkPoint& p1, SkScalar d0, SkScalar d1,
                     int side, SkPoint* offset0, SkPoint* offset1) {
    SkASSERT(side == -1 || side == 1);
    SkVector perp = SkVector::Make(p0.fY - p1.fY, p1.fX - p0.fX);
    if (SkScalarNearlyEqual(d0, d1)) {
        // if distances are equal, can just outset by the perpendicular
        perp.setLength(d0*side);
        *offset0 = p0 + perp;
        *offset1 = p1 + perp;
    } else {
        // Otherwise we need to compute the outer tangent.
        // See: http://www.ambrsoft.com/TrigoCalc/Circles2/Circles2Tangent_.htm
        if (d0 < d1) {
            side = -side;
        }
        SkScalar dD = d0 - d1;
        // if one circle is inside another, we can't compute an offset
        if (dD*dD >= p0.distanceToSqd(p1)) {
            return false;
        }
        SkPoint outerTangentIntersect = SkPoint::Make((p1.fX*d0 - p0.fX*d1) / dD,
                                                      (p1.fY*d0 - p0.fY*d1) / dD);

        SkScalar d0sq = d0*d0;
        SkVector dP = outerTangentIntersect - p0;
        SkScalar dPlenSq = dP.lengthSqd();
        SkScalar discrim = SkScalarSqrt(dPlenSq - d0sq);
        offset0->fX = p0.fX + (d0sq*dP.fX - side*d0*dP.fY*discrim) / dPlenSq;
        offset0->fY = p0.fY + (d0sq*dP.fY + side*d0*dP.fX*discrim) / dPlenSq;

        SkScalar d1sq = d1*d1;
        dP = outerTangentIntersect - p1;
        dPlenSq = dP.lengthSqd();
        discrim = SkScalarSqrt(dPlenSq - d1sq);
        offset1->fX = p1.fX + (d1sq*dP.fX - side*d1*dP.fY*discrim) / dPlenSq;
        offset1->fY = p1.fY + (d1sq*dP.fY + side*d1*dP.fX*discrim) / dPlenSq;
    }

    return true;
}

SkScalar SkPoint::distanceToLineBetweenSqd(const SkPoint& a,
                                           const SkPoint& b,
                                           Side* side) const {

    SkVector u = b - a;
    SkVector v = *this - a;

    SkScalar uLengthSqd = u.lengthSqd();
    SkScalar det = u.cross(v);
    if (side) {
        SkASSERT(-1 == SkPoint::kLeft_Side &&
                  0 == SkPoint::kOn_Side &&
                  1 == kRight_Side);
        *side = (Side) SkScalarSignAsInt(det);
    }
    return SkScalarMulDiv(det, det, uLengthSqd);
}