-- 作者：wenwu2008
-- 发布时间：12/11/2006 10:44:00 AM
--
我用过GDI+里面的GraphicsPath类，从那里面再转成SVG的path元素，会比较简单。只是我转弧形时，算的比较复杂。我把代码发上来吧。
public:
//将一个SVG中的扇形转成一个Graphics中的扇形,x_axis_rotation代表长半短轴顺时针旋转的角度，large_arc_flag代表是在圆还是小圆，sweep_flag代表是顺时针还是逆时针转动。
//假设存在严格匹配的扇形，不需要移动长半轴和短半轴
static void SVGArcToGDI(Drawing::Drawing2D ::GraphicsPath ^tagPath,Drawing::PointF startPoint,Drawing::PointF overPoint,float rx,float ry,float x_axis_rotation,float large_arc_flag,float sweep_flag)
{
//第一次解会得到
double t=2*(overPoint.Y -startPoint.Y)/ry;
double V=Math::Pow (((overPoint.Y-startPoint.Y )/ry),2)+(overPoint.X*overPoint.X-startPoint.X*startPoint.X ) /(rx*rx); //方程的三个系数
double A=4*Math::Pow ((startPoint.X-overPoint.X ),2)/Math::Pow (rx,4)+t*t/(rx*rx);
double B=4*(startPoint.X -overPoint.X )*V/(rx*rx)-t*t*2*startPoint.X /(rx*rx);
double C=V*V-t*t*(1-startPoint.X *startPoint.X /(rx*rx));
//得解为椭圆的中心点,
double PX_1,PY_1,PX_2,PY_2;
//当半径不够时，扩大半径，以达到拟合.
while(B*B-4*A*C<0)
{
rx*=1.01F;
ry*=1.01F;
V=Math::Pow (((overPoint.Y-startPoint.Y )/ry),2)+(overPoint.X*overPoint.X-startPoint.X*startPoint.X ) /(rx*rx);
A=4*Math::Pow ((startPoint.X-overPoint.X ),2)/Math::Pow (rx,4)+t*t/(rx*rx);
B=4*(startPoint.X -overPoint.X )*V/(rx*rx)-t*t*2*startPoint.X /(rx*rx);
C=V*V-t*t*(1-startPoint.X *startPoint.X /(rx*rx));
}
if(B*B-4*A*C>0)
{
//第一组
PX_1=((0-B)+Math::Pow ((B*B-4*A*C),0.5))/(2*A);
PY_1=startPoint.Y -ry*Math::Pow ((1- Math::Pow ((startPoint.X -PX_1),2)/(rx*rx) ),0.5);
if(Math::Abs ((Math::Pow ((overPoint.X -PX_1)/rx,2)+Math::Pow ((overPoint.Y -PY_1)/ry,2))-1)>0.00001)
PY_1=startPoint.Y +ry*Math::Pow ((1- Math::Pow ((startPoint.X -PX_1),2)/(rx*rx) ),0.5);
//第二组 PX_2=((0-B)-Math::Pow ((B*B-4*A*C),0.5))/(2*A);
PY_2=startPoint.Y -ry*Math::Pow ((1- Math::Pow ((startPoint.X -PX_2),2)/(rx*rx) ),0.5);
if(Math::Abs ((Math::Pow ((overPoint.X -PX_2)/rx,2)+Math::Pow ((overPoint.Y -PY_2)/ry,2))-1)>0.00001)
PY_2=startPoint.Y +ry*Math::Pow ((1- Math::Pow ((startPoint.X -PX_2),2)/(rx*rx) ),0.5);
}
else
{
if(B*B-4*A*C==0)
{
PX_1=((0-B)+Math::Pow ((B*B-4*A*C),0.5))/(2*A);
PX_2=PX_1;
PY_1=startPoint.Y -ry*Math::Pow ((1- Math::Pow ((startPoint.X -PX_1),2)/(rx*rx) ),0.5);
PY_2=startPoint.Y +ry*Math::Pow ((1- Math::Pow ((startPoint.X -PX_1),2)/(rx*rx) ),0.5);
if(Math::Abs ((Math::Pow ((overPoint.X -PX_2)/rx,2)+Math::Pow ((overPoint.Y -PY_2)/ry,2))-1)>0.00001)
PY_2=PY_1;
if(Math::Abs ((Math::Pow ((overPoint.X -PX_1)/rx,2)+Math::Pow ((overPoint.Y -PY_1)/ry,2))-1)>0.00001)
PY_1=PY_2;
//判断PY_2是否合理，如合理则继续，否则PY_2=PY_1;
}
}
Drawing::PointF P1=Drawing::PointF (Convert::ToSingle (PX_1),Convert::ToSingle (PY_1));
Drawing::PointF P2=Drawing::PointF (Convert::ToSingle (PX_2),Convert::ToSingle (PY_2));
Drawing::PointF center;
//为了判断四种情况，需要计算，先判断中心点在直线的左边还是右边
double k=(P1.X -startPoint.X )*(overPoint.Y-P1.Y)-(overPoint.X-P1.X )*(P1.Y -startPoint.Y );
if(large_arc_flag+sweep_flag==0||large_arc_flag+sweep_flag==2)//在左边
if(k>0)
center=Drawing::PointF (P1.X ,P1.Y );
else
center=Drawing::PointF (P2.X ,P2.Y );
else
if(k>0)
center=Drawing::PointF (P2.X ,P2.Y );
else
center=Drawing::PointF (P1.X ,P1.Y );
//得到center为最终椭圆中心
//求两点在椭圆上的位置
//求开始点所在的角度,确保结果大于0度
double dx=center.X -startPoint.X ;
double dy=center.Y -startPoint.Y ;
double startAngle=Math::Asin(dy/Math::Pow ((dx*dx+dy*dy),0.5))*180/Math::PI ;
if(dx>=0)
startAngle=180-startAngle;
else
if(dy<0)
startAngle+=360;
startAngle=360-startAngle;
//求终点所在的角度
dx=center.X -overPoint.X ;
dy=center.Y -overPoint.Y ;
double overAngle=Math::Asin(dy/Math::Pow ((dx*dx+dy*dy),0.5))*180/Math::PI ;
if(dx>=0)
overAngle=180-overAngle;
else
if(dy<0)
overAngle+=360;
overAngle=360-overAngle;
//如果是逆时钟,交换起末点
double swepAngle=overAngle-startAngle;
if(sweep_flag==0)
{
if(swepAngle>0)
swepAngle=0-swepAngle;
}
else
{
if(swepAngle<0)
swepAngle=0-swepAngle;
}
//必须保证弧的起点不变，可以使用转过负角来达到要求
tagPath->AddArc (center.X -rx,center.Y-ry,rx*2,ry*2,Convert::ToSingle (startAngle),Convert::ToSingle (swepAngle));
}
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