openGL的glutReshapeFunc()函数重绘时的问题 20C

写了一个opengl程序,画一个正六边形,想要实现无论怎样改变窗口的大小,六边形的形状大小位置都不变。
于是用glutReshapeFunc()得到窗口改变后的长与宽,然后再重新设置gluOrtho2D(),以实现一个像素对应一个坐标大小。
写好运行,发现改变窗口大小后,只有六边形的中心位置没有发生变化,而六边形的大小随窗口大小的改变在x,y方向上等比例**缩小**。
如果glutReshapeFunc()没有起作用的话,那么六边形也应该等比例在x,y方向上放大才对。但是现在却是缩小,有点搞不懂了,特来请教一下大家,下面附上代码:

 #include <GL/glut.h>
#include <math.h>
#include <stdlib.h>

const double TWO_PI = 6.2831853;

/* Intial display-window size.*/
GLsizei winWidth = 400, winHeight = 400;
GLuint regHex;

class screenPt
{
   private:
       GLint x,y;
    public:
    /* Default Constructor: initializes coordinate position to (0, 0).*/
    screenPt ( ) {
       x = y = 0;
    }
    void setCoords (GLint xCoord, GLint yCoord) {
       x = xCoord;
       y = yCoord;
    }
    GLint getx () const {
       return x;
    }
    GLint gety () const {
       return y;
    }
};
static void init (void)
{
    screenPt hexVertex, circCtr;
    GLdouble theta;
    GLint k;

    /* Set circle center coordinates.*/
    circCtr.setCoords (winWidth / 2, winHeight/2);

    glClearColor (1.0, 1.0, 1.0, 0.0);//Display-window color = white.

    /* Set up a display list for a red regular hexagon.
     * Vertices for the hexagon are Six equally spaced
     * points around the circumference of a circle.
     */
     regHex = glGenLists (1); // Get an identifier for the display list.
     glNewList (regHex, GL_COMPILE);
        glColor3f (1.0, 0.0, 0.0); // Set fill color for hexagon to red.
        glBegin (GL_POLYGON);
            for (k = 0; k < 6; k++){
            theta = TWO_PI * k / 6.0;
                hexVertex.setCoords (circCtr.getx () + 150 * cos (theta), circCtr.gety () + 150 * sin (theta));
                glVertex2i (hexVertex.getx (), hexVertex.gety ());
            }
        glEnd ();
    glEndList ();
}
void regHexagon (void)
{
    glClear (GL_COLOR_BUFFER_BIT);
    glCallList (regHex);
    glFlush();
}

void winReshapeFcn (int newWidth, int newHeight)
{
    glMatrixMode (GL_PROJECTION);
    glLoadIdentity ( );
    gluOrtho2D (0.0, (GLdouble) newWidth, 0.0, (GLdouble) newHeight);

    glClear (GL_COLOR_BUFFER_BIT);
}

int main (int argc, char** argv)
{
    glutInit (&argc, argv);
    glutInitDisplayMode (GLUT_SINGLE | GLUT_RGB);
    glutInitWindowPosition (100, 100);
    glutInitWindowSize (winWidth, winHeight);
    glutCreateWindow ("Reshape-Function & Display-List Example");

    init ( );
    glutDisplayFunc (regHexagon);
    glutReshapeFunc (winReshapeFcn);

    glutMainLoop ();
    return 0;
}

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