/// <summary>
/// 根据从路径起点开始的路径长度, 获取路径上的位置
/// </summary>
/// <param name="length"> 从路径起点开始的路径长度. 对于环状路径, 该长度可以为负值或大于路径长度的值 </param>
/// <param name="startSegmentIndex"> 建议起始查找的路径段索引（负值表示无建议）</param>
/// <param name="space"> 参数或返回值的相对空间 </param>
/// <returns> 路径在指定长度处的位置 </returns>
public Location GetLocationByLength(float length, int startSegmentIndex = -1, Space space = Space.World)
{
int lastSegmentIndex = _localSegments.Count - 1;
ValidatePathLength(lastSegmentIndex);
float totalLength = _localSegments[lastSegmentIndex].pathLength;
if (space == Space.World) length /= absWorldScale;
Location location = new Location();
// 处理计算长度
if (circular)
{
length = (totalLength + length % totalLength) % totalLength;
}
else
{
if (length <= 0)
{
return location;
}
if (length >= totalLength)
{
location.index = lastSegmentIndex;
location.time = 1f;
return location;
}
}
// 如果建议开始索引无效, 则重新估算开始索引
if (startSegmentIndex < 0 || startSegmentIndex > lastSegmentIndex)
{
location.index = (int)(length / totalLength * lastSegmentIndex);
}
else
{
location.index = startSegmentIndex;
}
// 查找样条索引, 并计算样条位置 t
if (_localSegments[location.index].pathLength > length)
{
do
{
if (location.index == 0)
{
location.time = _localSegments[0].GetLocationByLength(length);
return location;
}
} while (_localSegments[--location.index].pathLength > length);
location.time = _localSegments[location.index + 1].GetLocationByLength(length - _localSegments[location.index].pathLength);
location.index++;
}
else
{
while (_localSegments[++location.index].pathLength < length) ;
location.time = _localSegments[location.index].GetLocationByLength(length - _localSegments[location.index - 1].pathLength);
}
return location;
}
/// <summary>
/// 获取路径上指定位置的二阶导数
/// </summary>
/// <param name="location"> 路径位置 </param>
/// <param name="space"> 参数或返回值的相对空间 </param>
/// <returns> 指定位置的二阶导数 </returns>
public Vector3 GetSecondDerivative(Location location, Space space = Space.World)
{
Vector3 secondDerivative = _localSegments[location.index].GetSecondDerivative(location.time);
if (space == Space.Self) return secondDerivative;
else return TransformVector(secondDerivative);
}
/// <summary>
/// 获取路径上指定位置的切线. 切线是单位向量, 如果切线不存在返回 Vector3.zero
/// </summary>
/// <param name="location"> 路径位置 </param>
/// <param name="space"> 参数或返回值的相对空间 </param>
/// <returns> 指定位置的切线 </returns>
public Vector3 GetTangent(Location location, Space space = Space.World)
{
Vector3 tangent = _localSegments[location.index].GetTangent(location.time);
if (space == Space.Self) return tangent;
else return TransformDirection(tangent);
}
/// <summary>
/// 获取路径上指定位置的点坐标
/// </summary>
/// <param name="location"> 路径位置 </param>
/// <param name="space"> 参数或返回值的相对空间 </param>
/// <returns> 指定位置的点坐标 </returns>
public Vector3 GetPoint(Location location, Space space = Space.World)
{
Vector3 point = _localSegments[location.index].GetPoint(location.time);
if (space == Space.Self) return point;
else return TransformPoint(point);
}
