用 GDI+ 画 Chord

GDI+并没有提供GDI中的Chord函数（其它的还有RoundRect函数，可参考BobPowell 的这篇文章），只好自己动手了：

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BOOL GDIplusChord( HDC hDC, INT x1, INT y1, INT x2, INT y2, INT x3, INT y3, INT x4, INT y4 ) {     Graphics graphics(hDC);     CRect rectBound(x1, y1, x2, y2);     rectBound.NormalizeRect();     Rect ellipseRect(rectBound.left, rectBound.top, rectBound.Width(), rectBound.Height());       ////////////////////////////////////////////////////////////////////////////////     // For testing only.     BYTE        byAlpha = 200;     SolidBrush  fillBrush(Color(byAlpha, 0, 0, 255));     Pen         redPen(Color(byAlpha, 255, 0, 0), 3);     ////////////////////////////////////////////////////////////////////////////////     Status ret = InvalidParameter;       if ( x3 == x4 && y3 == y4 )     {         // If the starting point and ending point of the curve are the same, a complete ellipse should be drawn.         ret = graphics.FillEllipse(&fillBrush, ellipseRect);         ret = graphics.DrawEllipse(&redPen, ellipseRect);         return Gdiplus::Ok == ret;     }       CPoint ptCenter(rectBound.CenterPoint());   #define PI 3.1415926       REAL startAngle = atan2(y3-ptCenter.y, x3-ptCenter.x ) * 180.0f / PI;     REAL sweepAngle = (atan2(y4-ptCenter.y, x4-ptCenter.x ) * 180.0f / PI) - startAngle - 360.0f;     if ( sweepAngle < -360.0f )         sweepAngle += 360.0f;           GraphicsPath path;     path.StartFigure();     path.AddArc(ellipseRect, startAngle, sweepAngle);     path.CloseFigure();       ret = graphics.FillPath(&fillBrush, &path);     ret = graphics.DrawPath(&redPen, &path);           return Gdiplus::Ok == ret; }