In Windows, the GDI function pie

Msdn explanation:

Pie

ThePieFunction 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);

I didn't understand it for a long time. I used pie to draw two figures to figure out the true meaning of the parameters:

Nleftrect, ntoprect, nrightrect, and nbottomrect determine a rectangle, and the fan-shaped center (center of the circle) is the center of the rectangle, which is recorded as O.

Nxradial1, nyradial1 identifies a vertex and records it as a. There is an OA Ray

Nxradial and nyradial determine a point. If it is recorded as B, ob rays exist.
In this way, there is a fan-shaped OA string and a fan-shaped OAB with OB as the final string.