/// <summary>
/// Shifts the spline with <paramref name="amount"/> distance and returns a new spline
/// </summary>
/// <param name="safeDist">
/// The max distance between the middle of the curves and their extreme points.
/// If your shifted curve has too many sharp edges try pumping this number up.
/// But beware because it causes it to have more points and thus decreasing performance.
/// </param>
/// <param name="newSpline">If you want the returned spline to be put into an already existing spline assign this parameter.</param>
public BezierSpline GetShiftedSpline(float amount, float safeDist = 0.3f, BezierSpline newSpline = null)
{
BezierSpline _shiftedSpline;
if (newSpline != null)
{
_shiftedSpline = newSpline;
}
else
{
_shiftedSpline = new GameObject().AddComponent <BezierSpline>();
}
_shiftedSpline.Clear();
_shiftedSpline.name = "Lane" + amount;
// So, you cannot offset a Bézier curve perfectly with another Bézier curve, no matter how high-order you make that
// other Bézier curve. However, we can chop up a curve into "safe" sub-curves (where safe means that all the control
// points are always on a single side of the baseline, and the midpoint of the curve at t=0.5 is roughly in the centre
// of the polygon defined by the curve coordinates) and then point-scale each sub-curve with respect to its scaling
// origin (which is the intersection of the point normals at the start and end points).
// A good way to do this reduction is to first find the curve's extreme points, and use these as initial splitting points.
// After this initial split, we can check each individual segment to see if it's "safe enough" based on where the
// center of the curve is.If the on-curve point for t = 0.5 is too far off from the center, we simply split the
// segment down the middle. Generally this is more than enough to end up with safe segments.
Vector3 _p0 = points[0];
Vector3 _p1, _p2, _p3;
List <Vector3[]> _newPointsSpline = new List <Vector3[]>();
for (int i = 3; i < PointCount; i += 3)
{
_p1 = points[i - 2];
_p2 = points[i - 1];
_p3 = points[i];
// roots of our cubic bezier curve to find extremes
SortedSet <float> _solutions = new SortedSet <float>();
{
float?_sol1, _sol2;
BezierMath.CubicGetRoots(_p0.x, _p1.x, _p2.x, _p3.x, out _sol1, out _sol2);
if (_sol1.HasValue && _sol1.Value < 1 && _sol1.Value > 0)
{
_solutions.Add(_sol1.Value);
}
if (_sol2.HasValue && _sol2.Value < 1 && _sol2.Value > 0)
{
_solutions.Add(_sol2.Value);
}
BezierMath.CubicGetRoots(_p0.y, _p1.y, _p2.y, _p3.y, out _sol1, out _sol2);
if (_sol1.HasValue && _sol1.Value < 1 && _sol1.Value > 0)
{
_solutions.Add(_sol1.Value);
}
if (_sol2.HasValue && _sol2.Value < 1 && _sol2.Value > 0)
{
_solutions.Add(_sol2.Value);
}
BezierMath.CubicGetRoots(_p0.z, _p1.z, _p2.z, _p3.z, out _sol1, out _sol2);
if (_sol1.HasValue && _sol1.Value < 1 && _sol1.Value > 0)
{
_solutions.Add(_sol1.Value);
}
if (_sol2.HasValue && _sol2.Value < 1 && _sol2.Value > 0)
{
_solutions.Add(_sol2.Value);
}
}
// the list of new points of the offset curve
List <Vector3[]> _newPointsCurve = new List <Vector3[]>();
// So we're gonna need to split the starting curve at potentially more points
// We do that by splitting in order and always taking the second split curve as the next
// starting curve
{
Vector3[] _first, _second = new Vector3[] { _p0, _p1, _p2, _p3 };
float _secondSize = 1f; // we need this to know how big the second curve is compared to the very first starting curve
// so we can split at the right point
foreach (float sol in _solutions)
{
BezierMath.CubicSplitCurve(_second[0], _second[1], _second[2], _second[3], _secondSize * sol, out _first, out _second);
_secondSize *= (1f - sol);
_newPointsCurve.Add(_first);
}
_newPointsCurve.Add(_second); // no more calculations with the second curve, so we can add it to the list
}
// check whether each bezier curve is safe or not if not split it
{
int _at = _newPointsCurve.Count - 1;
while (_at >= 0)
{
Vector3[] _split1, _split2;
// where the curv t = 0.5f
Vector3 _zeroDotFive = BezierMath.CubicGetPoint(_newPointsCurve[_at][0], _newPointsCurve[_at][1],
_newPointsCurve[_at][2], _newPointsCurve[_at][3], 0.5f);
// the center of the curve's 4 points
Vector3 _center = (_newPointsCurve[_at][0] + _newPointsCurve[_at][1] + _newPointsCurve[_at][2] + _newPointsCurve[_at][3]) / 4f;
// if they are too far away
if (Vector3.Distance(_zeroDotFive, _center) > safeDist)
{
// split curva at 0.5f
BezierMath.CubicSplitCurve(_newPointsCurve[_at][0], _newPointsCurve[_at][1], _newPointsCurve[_at][2], _newPointsCurve[_at][3], 0.5f,
out _split1, out _split2);
// overwrite current curve
_newPointsCurve[_at] = _split2;
// add one before it
_newPointsCurve.Insert(_at, _split1);
// we need to check the _split too again as well, so add one to at
_at++;
}
else
{
// no problem with this curve, move on
_at--;
}
}
}
// scale
{
Vector3 _pivot;
for (int k = 0; k < _newPointsCurve.Count; k++)
{
// get pivot -> the intersection of the point normals at the start and end points
bool _doIntersect = Math3D.LineLineIntersection(
out _pivot,
_newPointsCurve[k][0],
(Quaternion.LookRotation(Vector3.right) * BezierMath.CubicGetFirstDerivative(_newPointsCurve[k][0], _newPointsCurve[k][1], _newPointsCurve[k][2], _newPointsCurve[k][3], 0.01f)).normalized,
_newPointsCurve[k][3],
(Quaternion.LookRotation(Vector3.right) * BezierMath.CubicGetFirstDerivative(_newPointsCurve[k][0], _newPointsCurve[k][1], _newPointsCurve[k][2], _newPointsCurve[k][3], 0.99f)).normalized
);
// scaling
if (!_doIntersect) // it's essentially a line
// which way the right is from the line
{
Vector3 _whichWay = Vector3.Cross(_newPointsCurve[k][3] - _newPointsCurve[k][0], Vector3.up).normalized;
for (int j = 0; j < _newPointsCurve[k].Length; j++)
{
_newPointsCurve[k][j] -= _whichWay * amount;
}
}
else
{
// cache this
Vector3 _middleDerivative = BezierMath.CubicGetFirstDerivative(
_newPointsCurve[k][0],
_newPointsCurve[k][1],
_newPointsCurve[k][2],
_newPointsCurve[k][3], 0.5f);
// which way is the middle point's right
Vector3 _curveMiddleRight = (Quaternion.LookRotation(Vector3.right) * _middleDerivative).normalized;
// which way is the middle point's left
Vector3 _curveMiddleLeft = (Quaternion.LookRotation(Vector3.left) * _middleDerivative).normalized;
for (int j = 0; j < _newPointsCurve[k].Length; j++)
{
Vector3 _scaleDir = (_pivot - _newPointsCurve[k][j]).normalized;
// pivot is to the right
bool _isPivotToRight = Vector3.Angle(_scaleDir, _curveMiddleRight) <
Vector3.Angle(_scaleDir, _curveMiddleLeft);
// move to position based on pivot direction
if (_isPivotToRight)
{
_newPointsCurve[k][j] += _scaleDir * amount;
}
else
{
_newPointsCurve[k][j] -= _scaleDir * amount;
}
}
}
}
}
_newPointsSpline.AddRange(_newPointsCurve);
_p0 = _p3;
}
_shiftedSpline.points = new Vector3[_newPointsSpline.Count * 3 + 1];
_shiftedSpline.points[0] = _newPointsSpline[0][0];
_shiftedSpline.modes = new BezierControlPointMode[_newPointsSpline.Count + 1];
_shiftedSpline.modes[0] = BezierControlPointMode.Free;
for (int i = 0; i < _newPointsSpline.Count; i++)
{
_shiftedSpline.modes[i + 1] = BezierControlPointMode.Free;
for (int k = 1; k <= 3; k++)
{
_shiftedSpline.points[i * 3 + k] = _newPointsSpline[i][k];
}
}
return(_shiftedSpline);
}