사각형 좌우로 이동시키는거 ㅜㅜㅜ흑흑흑

[응응응(59.20)]

사각형을 좌우로 움직여야 되는데
왼쪽으로 안움직여요  ㅜㅜ흑흑
어떻게 하면 좌우로 움직이게 할 수 있을까요
고수님들 제발 도와주세요 ㅜㅜ

#include <glut.h>
#include <gl.h>
#include <glu.h>

GLfloat Delta = 0.0;

void MyDisplay()
{
 glClear(GL_COLOR_BUFFER_BIT);
 glBegin(GL_POLYGON);
  glColor3f(0.0, 0.5, 0.9);
  glVertex3f(-1.0 + Delta, -0.5, 0.0);
  glVertex3f(0.0 + Delta, -0.5, 0.0);
  glVertex3f(0.0 + Delta, 0.5, 0.0);
  glVertex3f(-1.0 + Delta, 0.5, 0.0);
 glEnd();
 glutSwapBuffers();
}

void MyTimer(int Value)
{

 Delta = Delta + 0.01;
 if (Delta >= 1)
  Delta = Delta - 0.1;
 else if (Delta <= -1)
  Delta = Delta + 0.1;
 glutPostRedisplay();
 glutTimerFunc(40, MyTimer, 1);

 
}

int main(int argc, char** argv)
 {
 glutInit(&argc,argv);
 glutInitDisplayMode(GLUT_RGB|GLUT_DOUBLE);//Doubel->SwapBuffers
 glutInitWindowSize(300,300);
 glutInitWindowPosition(0,0);
 glutCreateWindow(\"OpenGL Drawing Example\");
 glClearColor (1.0, 1.0, 1.0, 1.0);
 glMatrixMode(GL_PROJECTION);
 glLoadIdentity();
 glOrtho(-1.0, 1.0, -1.0, 1.0, -1.0, 1.0);
 glutDisplayFunc(MyDisplay);
 glutTimerFunc(40, MyTimer, 1);
 glutMainLoop();
 return 0;
}