问如何用C语言绘制多边形？

EN

gdImagePolygon(gdImagePtr im, gdPointPtr points, int pointsTotal, int color)

typedef struct {
    int x, y;
} gdPoint, *gdPointPtr;

... inside a function ...
gdImagePtr im;
int black;
int white;
/* Points of polygon */
gdPoint points[3];           // an array of gdPoint structures is used here
im = gdImageCreate(100, 100);
/* Background color (first allocated) */
black = gdImageColorAllocate(im, 0, 0, 0);  
/* Allocate the color white (red, green and 
  blue all maximum). */
white = gdImageColorAllocate(im, 255, 255, 255);  
/* Draw a triangle. */
points[0].x = 50;
points[0].y = 0;
points[1].x = 99;
points[1].y = 99;
points[2].x = 0;
points[2].y = 99;
gdImagePolygon(im, points, 3, white);
/* ... Do something with the image, such as 
  saving it to a file... */
/* Destroy it */
gdImageDestroy(im);

int Draw_Polygon (int Side, ...)
{
    va_list Ap;
    va_start (Ap, Side);
    int X_1 = va_arg (Ap, int);
    int X_0 = X_1;
    int Y_1 = va_arg (Ap, int);
    int Y_0 = Y_1;
    int Cnt;
    for (Cnt = 0; Cnt < Side-1; Cnt++)
    {
        int X_2 = va_arg (Ap, int);
        int Y_2 = va_arg (Ap, int);
        gdImageLine ( gdImage, X_1, Y_1, X_2, Y_2, blue);
        X_1 = X_2;
        Y_1 = Y_2;
    }
    gdImageLine ( gdImage, X_1, Y_1, X_0, Y_0, blue);
    va_end(Ap);
    return 0;
}

int main (void)
{
    if (Draw_Polygon (5, 0, 0, 0, 10, 12, 12, 16, 8, 5, 0) == 0) // Draw a pentagon.
    {
         // Success !
    }

    if (Draw_Polygon (6, 0, 0, 0, 10, 12, 12, 16, 8, 6, 3, 5, 0) == 0) // Draw a hexagon.
    {
         // Success !
    }
}

Procedure DrawPol (integer N,L)
  Integer i
  For i=1 To N
    Draw (L)
    Turn (360/N)
  EndFor
EndProcedure

Real CurrentAngle = 0  /* global variable */
Integer CurrentX = MAXX / 2  /* last point drawn */ 
Integer CurrentY = MAXY / 2  /* initialized to the center of the paint area */

Procedure Draw (Integer L)
  Integer FinalX,FinalY
  FinalX = CurrentX + L*cos(CurrentAngle)
  FinalY = CurrentY + L*sin(CurrentAngle)
  Line (CurrentX, CurrentY, FinalX, FinalY)  /* gdImageLine() function actually */
  CurrentX = FinalX
  CurrentY = FinalY
EndProcedure

Procedure Turn (Float A)
  CurrentAngle = CurrentAngle + A
  If (CurrentAngle>360)              /* MOD operator usually works */
    CurrentAngle = 360-CurrentAngle  /* only for integers */ 
  EndIf
EndProcedure