OpenGL显示窗口重定形函数

    我们在建立初始显示窗口后，需要在其后改变位置与形状。窗口尺寸的改变可能改变其纵横比并引起对象形状的改变。所以GLUT库提供glutReshapeFunc(winReshapeFcn)函数。和其他GLUT函数一起放在程序的主过程中，不过该函数是在窗口尺寸输入后激活。其参数是接受新窗口高度的过程名。还可以接着使用新尺寸去重新设置投影参数并完成任何其他操作，包括改变显示窗口颜色。另外，可以保存宽度和高度供其它子程序使用。

void glutReshapeFunc(void (*func)(int width, int height));

    官方文档在这里。

#include <GL/glut.h>
#include <cmath>
#include <cstdlib>

const double TWO_PI = 6.2831853;

GLsizei winWidth = 400, winHeight = 400;
GLuint regHex;

class screenPt {
private:
    GLint x, y;

public:
    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;

    circCtr.setCoords(winWidth/2, winHeight/2);

    glClearColor(1.0, 1.0, 1.0, 0.0);

    regHex = glGenLists(1);
    glNewList(regHex, GL_COMPILE);
    glColor3f(1.0, 0.0, 0.0);
    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()
{
    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;
}