C#基数样条曲线的模拟实现(对应Graphics的DrawCurve)
C#的绘图函数中有一个绘制样条曲线的函数DrawCurve，当只传入Pen和Point数组时，采用的是基数样条曲线绘制。如果只是绘制样条曲线，那这个函数已经满足了。但是项目中要求不但要绘制曲线，还要将曲线以方格的形式模拟来实现。为此，就必须知道样条曲线是如何绘制的，才有办法知道都有哪些点，然后再用格子来模拟。
起初，使用了很粗暴的方法，即使用DrawCurve在内存中绘制到Image中，然后从Image中取出黑白点，然后形成黑白点的矩阵，进而利用这些矩阵点对应到像素点来绘制方格。做了简单的实现，但效果不理想。原因有几个。
1.不断使用内存绘制到Image中需要消耗大量的内存。
2.利用像素点来采集矩阵的点时，难以确定一个采集的范围。
3.至少需要对像素进行X和Y的双重循环遍历才能达成，这样时间复杂度会随着X、Y的增加而不断加大。
后面找到了一份模拟实现，经过改造，初步达成了目的。来看看模拟实现的和DrawCurve的拟合效果图，见下图。
注：图中黑色部分使用DrawCurve来绘制，黑色线中间的白色部分采用的是模拟绘制。从测试的结果来看，符合程度比较理想。下面是实现的代码。
using System;
using System.Collections.Generic;
using System.Drawing;
using System.Linq;
using System.Text;
namespace SplineTest
{
///
/// 样条曲线。每根样条曲线包含4个控制点
///
public class Spline
{
///
/// 样点数。在点Pk和Pk+1之间，将会生成若干个样点。所以"u"将会从0.00F增长到0.05F.
///
private static readonly int _samplePointCount = 20;
///
/// 在基数算法中的t
///
private static readonly float _tension = 0.0F;
#region 属性
private PointF _startControlPoint;
///
/// "Pk-1"点(起始控制点)
///
public PointF StartControlPoint
{
get
{
return this._startControlPoint;
}
set
{
this._startControlPoint = value;
}
}
private PointF _startPoint;
///
/// "Pk"点(起始点)
///
public PointF StartPoint
{
get
{
return this._startPoint;
}
set
{
this._startPoint = value;
}
}
private PointF _endPoint;
///
/// "Pk+1"点(结束点)
///
public PointF EndPoint
{
get
{
return this._endPoint;
}
set
{
this._endPoint = value;
}
}
private PointF _endControlPoint;
///
/// "Pk+2"点(结束控制点)
///
public PointF EndControlPoint
{
get
{
return this._endControlPoint;
}
set
{
this._endControlPoint = value;
}
}
private PointF[] _ctrlPoints;
///
/// 曲线点(控制点及模拟的样点)
///
public PointF[] CtrlPoints
{
get
{
return this._ctrlPoints;
}
}
private bool _isFirst = false;
///
/// 标识当前样条曲线是否是第一条，如果是m_startControlPoint 和 m_startPoint将会相同。
/// 因为在Pk和Pk+1之间需要4个点来决定样条曲线，所以我们需要在Pk-1点前手动添加一个点。
/// 这样我们才能在Pk-1和Pk+1之间绘制样条曲线。
/// 同样的，最后一根样条曲线的Pk+2点会与它的"Pk+1"点相同，
/// 这样我们才能在Pk+1和Pk+2之间绘制样条曲线。
///
public bool IsFirst
{
get
{
return this._isFirst;
}
set
{
this._isFirst = value;
}
}
#endregion
public Spline()
{
_startControlPoint = new PointF();
_startPoint = new PointF();
_endPoint = new PointF();
_endControlPoint = new PointF();
_ctrlPoints = new PointF[_samplePointCount + 1];
for (int i = 0; i < _ctrlPoints.Length; i++)
{
_ctrlPoints[i] = new PointF();
}
}
///
///添加关节。将新控制点添加到控制点列表中，并更新前面的样条曲线。
///
/// 前一根样条曲线
/// 当前点
public void AddJoint(Spline prevSpline, PointF currentPoint)
{
//前一根样条曲线(prevSpline)为null，说明控制点列表中只有一个点，所以4个控制点样同。
//当第2个及之后的控制点添加到控制点列表中时，那第1根样条曲线的Pk+1和Pk+2点需要更新
if (null == prevSpline)
{
this._startControlPoint = currentPoint;
this._startPoint = currentPoint;
this._endPoint = currentPoint;
this._endControlPoint = currentPoint;
this._isFirst = true;
}
else//前一根样条曲线不为null，所以更新前一根样条曲线的控制点列表，同时更新当前样条曲线的控制点列表。
{
//前一根样条曲线是第1根样条曲线，更新它的Pk+1和Pk+2点
if (true == prevSpline._isFirst)
{
this._startControlPoint = prevSpline.StartControlPoint;
this._startPoint = prevSpline.StartPoint;
this._endPoint = currentPoint;
this._endControlPoint = currentPoint;
GenerateSamplePoint();
return;
}
else///前一根样条曲线不是第1根样条曲线，仅更新它的Pk+2点
{
prevSpline.EndControlPoint = currentPoint;
prevSpline.GenerateSamplePoint();
//模拟当前样条曲线的样点
this._startControlPoint = prevSpline._startPoint;
this._startPoint = prevSpline._endPoint;
this._endPoint = currentPoint;
this._endControlPoint = currentPoint;
GenerateSamplePoint();
}
}
}
///
/// 使用基数算法生成样点
///
public void GenerateSamplePoint()
{
PointF startControlPoint = this.StartControlPoint;
PointF startPoint = this.StartPoint;
PointF endPoint = this.EndPoint;
PointF endControlPoint = this.EndControlPoint;
float step = 1.0F / (float)_samplePointCount;
float uValue = 0.00F;
for (int i = 0; i < _samplePointCount; i++)
{
PointF pointNew = GenerateSimulatePoint(uValue, startControlPoint, startPoint, endPoint, endControlPoint);
this.CtrlPoints[i] = pointNew;
uValue += step;
}
this.CtrlPoints[_ctrlPoints.Length - 1] = endPoint;
}
///
/// 绘制样条曲线
///
///
public void Draw(Graphics g, Pen pen)
{
for (int i = 0; i < _ctrlPoints.Length - 1; i++)
{
PointF lastPoint = _ctrlPoints[i];
PointF nextPoint = _ctrlPoints[i + 1];
g.DrawLine(pen, lastPoint, nextPoint);
}
}
#region GenerateSimulatePoint
///
/// 生成曲线模拟点，该点在startPoint和endPoint之间
///
/// 介于0和1之间的变量
/// 起始点startPoint之前的控制点, 协助确定曲线的外观
/// 目标曲线的起始点startPoint,当u=0时，返回结果为起始点startPoint
/// 目标曲线的结束点endPoint, 当u=1时,返回结果为结束点endPoint
/// 在起结点startPoint之后的控制点, 协助确定曲线的外观
/// 返回介于startPoint和endPoint的点
private PointF GenerateSimulatePoint(float u,
PointF startControlPoint,
PointF startPoint,
PointF endPoint,
PointF endControlPoint)
{
float s = (1 - _tension) / 2;
PointF resultPoint = new PointF();
resultPoint.X = CalculateAxisCoordinate(startControlPoint.X, startPoint.X, endPoint.X, endControlPoint.X, s, u);
resultPoint.Y = CalculateAxisCoordinate(startControlPoint.Y, startPoint.Y, endPoint.Y, endControlPoint.Y, s, u);
return resultPoint;
}
///
/// 计算轴坐标
///
///
///
///
///
///
///
///
/// 获取样条曲线上的点
///
///
///
///
public static List FetchPoints(PointF[] points)
{
if (points == null || points.Length <= 0)
{
return null;
}
List _splines = new List();
Spline splineNew = null;
Spline lastNew = null;
foreach (PointF nowPoint in points)
{
if (null == _splines || 0 == _splines.Count)
{
splineNew = new Spline();
splineNew.AddJoint(null, nowPoint);
_splines.Add(splineNew);
}
else
{
splineNew = new Spline();
lastNew = _splines[_splines.Count - 1] as Spline;
splineNew.AddJoint(lastNew, nowPoint);
_splines.Add(splineNew);
};
}
List _points = new List();
foreach (Spline spline in _splines)
{
if (spline.IsFirst)
{
continue;
}
foreach (PointF point in spline.CtrlPoints)
{
if (_points.Contains(point))
{
continue;
}
_points.Add(point);
}
}
return _points;
}
}
///
/// Graphics扩展
///
public static class GraphicsExtension
{
///
/// 绘制样条曲线
///
///
///
///
public static void DrawSpline(this Graphics g, Pen pen, PointF[] points)
{
if (g == null)
{
return;
}
if (pen == null)
{
return;
}
if (points == null || points.Length <= 0)
{
return;
}
List _splines = new List();
Spline splineNew = null;
Spline lastNew = null;
foreach (PointF nowPoint in points)
{
if (null == _splines || 0 == _splines.Count)
{
splineNew = new Spline();
splineNew.AddJoint(null, nowPoint);
_splines.Add(splineNew);
}
else
{
splineNew = new Spline();
lastNew = _splines[_splines.Count - 1];
splineNew.AddJoint(lastNew, nowPoint);
_splines.Add(splineNew);
}
}
Spline spline = null;
for (int i = 0; i < _splines.Count; i++)
{
spline = _splines[i];
if (spline.IsFirst)
{
continue;
}
spline.Draw(g, pen);
}
}
}
}
1.Spline部分最核心的算法是CalculateAxisCoordinate，网上有很多类似的实现，但都不理想，这个是比较理想的一个。
2.为了便于在Graphics中直接调用，这里对Graphics增加了一个扩展方法DrawSpline，这样就可以像调用DrawCurve一样调用，即g.DrawSpline(pen,points).
3.在绘制出样条曲线后，还需要能得到其所模拟的点，于是在Spline中增加了一个FetchPoints的方法。
转载请注明出处http://blog.csdn.net/xxdddail/article/details/47662983。