OpenGL鼠标控制绘制矩形

#include <windows.h>    // Windows的头文件

#include <gl\gl.h>        // OpenGL32库的头文件
#include <gl\glu.h>        // GLu32库的头文件
#include <gl\glaux.h>    // GLaux库的头文件
#include <gl\glut.h>    // Glut库头文件

#pragma comment( lib, "opengl32.lib")    // OpenGL32连接库
#pragma comment( lib, "glu32.lib")        // GLu32连接库
#pragma comment( lib, "glaux.lib")        // GLaux连接库
#pragma comment( lib, "glut.lib")        // Glut链接库

struct GLintPoint
{
    GLint x,y;

};

GLintPoint corner[2];
bool selected = false;
int screenWidth=640;
int screenHeight=480;

void myDisplay()
{
    glClear(GL_COLOR_BUFFER_BIT);
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();
    glColor3f(1.0f,1.0f,1.0f);
    if(selected)
    {
        glBegin(GL_QUADS);
        glVertex2i(corner[0].x,corner[0].y);
        glVertex2i(corner[0].x,corner[1].y);
        glVertex2i(corner[1].x,corner[1].y);
        glVertex2i(corner[1].x,corner[0].y);
        glEnd();    
    }
    glutSwapBuffers();

}

void myMouse(int button,int state,int x,int y)
{
    if(button==GLUT_LEFT_BUTTON && state==GLUT_DOWN)
    {
        corner[0].x=x;
        corner[0].y=screenHeight-y;
        selected=true;
    }
    glutPostRedisplay();

}

void myPassiveMotion(int x,int y)
{
    corner[1].x=x;
    corner[1].y=screenHeight-y;
    glutPostRedisplay();

}

int main(int argc,char **argv)
{
    glutInit(&argc,argv);
    glutInitWindowSize(screenWidth,screenHeight);
    glutInitWindowPosition(0,0);
    glutInitDisplayMode(GLUT_RGB | GLUT_DOUBLE);
    glutCreateWindow("Rubber Rect Demo");

    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    gluOrtho2D(0,screenWidth,0,screenHeight);
    glMatrixMode(GL_MODELVIEW);
    glClearColor(0.0f,0.0f,0.0f,0.0f);
    glViewport(0,0,screenWidth,screenHeight);

    glutMouseFunc(myMouse);
    glutDisplayFunc(myDisplay);
    glutPassiveMotionFunc(myPassiveMotion);
    
    glutMainLoop();
    return 0;

}