windows 中 gdi 函數 pie

MSDN解釋：

Pie

The Pie function draws a pie-shaped wedge bounded by the intersection of an ellipse and two radials. The pie is outlined by using the current pen and filled by using the current brush.

BOOL Pie(  HDC hdc,         // handle to DC  int nLeftRect,   // x-coord of upper-left corner of rectangle  int nTopRect,    // y-coord of upper-left corner of rectangle  int nRightRect,  // x-coord of lower-right corner of rectangle  int nBottomRect, // y-coord of lower-right corner of rectangle  int nXRadial1,   // x-coord of first radial's endpoint  int nYRadial1,   // y-coord of first radial's endpoint  int nXRadial2,   // x-coord of second radial's endpoint  int nYRadial2    // y-coord of second radial's endpoint);

看半天沒有理解，用Pie畫了兩個圖才搞清楚參數的真正涵義：

nLeftRect, nTopRect , nRightRect,  nBottomRect 確定了一個矩形，而扇形的扇心（所在圓的圓心）就是這個矩形的中心，記作O。

 nXRadial1,  nYRadial1確定了一個點，記作A，則有OA射線，同樣

 nXRadial2,  nYRadial2確定了一個點，記作B，則有OB射線
這樣，就有了扇形OA為弦和以OB為終弦的扇形OAB。