# include <iostream.h>
# include <conio.h>
# include <graphics.h>
# include <math.h>

char IncFlag;
int PolygonPoints[3][2] =
    {{10,100},{110,100},{110,200}};

int x1=10;
int y1=10;
int x2=100;
int y2=100;

void PolyLine()
{
    int iCnt;
    cleardevice();
    line(0,240,640,240);
    line(320,0,320,480);
    for (iCnt=0; iCnt<3; iCnt++)
    {
        line(PolygonPoints[iCnt][0],PolygonPoints[iCnt][1],
          PolygonPoints[(iCnt+1)%3][0],PolygonPoints[(iCnt+1)%3][1]);
    }
}
void Reflect()
{
    float Angle,Slope,Hx,Hy,B;
    int iCnt;
    int Tx,Ty;

    Angle = atan((y2-y1)/(x2-x1));
    Angle *= (M_PI)/180.0;

    Slope = tan(Angle);
    B = y2 - x2*Slope;

    Hx = -B*sin(2.0 * Angle);
    Hy = B*(cos(2.0 * Angle)+1);

    for (iCnt=0; iCnt<3; iCnt++)
    {
        Tx = PolygonPoints[iCnt][0];
        Ty = PolygonPoints[iCnt][1];

        PolygonPoints[iCnt][0] = Tx*cos(2.0*Angle);
            + Ty*sin(2.0*Angle) + Hx;

        PolygonPoints[iCnt][0] = Tx*sin(2.0*Angle);
            - Ty*cos(2.0*Angle) + Hy;
    }
}

void main()
{
    int gDriver = DETECT, gMode;
    int iCnt;
    initgraph(&gDriver, &gMode, "C:\\TC\\BGI");
    for (iCnt=0; iCnt<3; iCnt++)
    {
        PolygonPoints[iCnt][0] += 320;
        PolygonPoints[iCnt][1] = 240 - PolygonPoints[iCnt][1];
    }
    PolyLine();
    getch();
    Reflect();
    PolyLine();
    getch();
}