OpenGL实现鼠标移动方块

#include <GL/glut.h>
#include "Graphics.h"
 
int x1 = 0, y1 = 0, x2 = 100, y2 = 100; //方块的左下角坐标和右上角坐标
int x = 0, y = 0; //鼠标位置
int dx = 0, dy = 0; //鼠标位移
int b = 0;  //判断鼠标是否在方块内
 
void init()
{
  glMatrixMode(GL_PROJECTION);
  gluOrtho2D(0.0, 800.0, 0.0, 800.0); //窗口左下角的世界坐标系为 （0，0）
  glClearColor(1.0f, 1.0f, 1.0f, 1.0f);
}
 
void test()
{
  glClear(GL_COLOR_BUFFER_BIT);
  glColor3f(1.0f, 0.0f, 0.0f);
  glRecti(x1, y1, x2, y2);
  glutSwapBuffers();
}
 
int inRect(int xMouse, int yMouse)
{
  yMouse = 800 - yMouse;
  if (xMouse < x2 && xMouse > x1 && yMouse < y2 && yMouse > y1)
 return 1;
  else
 return 0;
}
 
void myMouse(int button, int state, int xMouse, int yMouse)
{
  if (button == GLUT_LEFT_BUTTON && state == GLUT_DOWN) {
 x = xMouse; //xMouse, yMouse是以窗口的左上角为原点（0，0）的窗口坐标系中的点
 y = yMouse;
 if (inRect(x, y)) b = 1;
  }
  if (button == GLUT_LEFT_BUTTON && state == GLUT_UP) b = 0; //当移动较快时鼠标会在刷新间隔移出方块，所以用DOWN和UP来判断鼠标在方块内
}
 
void moveMouse(int xMouse, int yMouse)
{
  if (b) {
 dx = xMouse - x;
 dy = yMouse - y;
 x1 = x1 + dx;
 x2 = x2 + dx;
 y1 = y1 - dy; //鼠标的窗口坐标系和世界坐标系的Y轴相反，所以鼠标向Y轴的正方向移动的时候，在世界坐标系是向Y轴的负方向移动
 y2 = y2 - dy;
 x = xMouse;
 y = yMouse;
  }
}
 
int main(int argc, char** argv)
{
  glutInit(&argc, argv);
  glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB);
  glutInitWindowPosition(0, 0); 
  glutInitWindowSize(800, 800);
  glutCreateWindow("Move Square");
  init();
  glutDisplayFunc(test);
  glutIdleFunc(test); //移动是动画，为了流畅，必须开这个
  glutMouseFunc(myMouse);
  glutMotionFunc(moveMouse);
  glutMainLoop();
 
  return 0;
}