#include <GL/glut.h>

float x_position = 0;
float speed = 0.1f;

void display()
{
 glClear(GL_COLOR_BUFFER_BIT);

 glTranslatef(x_position, 0, 0);

 glColor3f(1, 0, 0);
 glBegin(GL_QUADS);
  glVertex2f(-2, 2);
  glVertex2f(2, 2);
  glVertex2f(2, -2);
  glVertex2f(-2, -2);
 glEnd();
 glutSwapBuffers();
}

void teclado(unsigned char key, int x, int y) {
 glutPostRedisplay();

 if (key == 27) {
  exit(0);
 }
 if (key == 97) {
  x_position = -speed;
 }
 if (key == 100) {
  x_position = speed;
 }
}

int main(int argc, char** argv)
{
 glutInit(&argc;, argv);
 glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGBA);
 glutInitWindowSize(640, 640);
 glutCreateWindow("OpenGL");
 glutDisplayFunc(display);
 glutKeyboardFunc(teclado);
 gluOrtho2D(-10, 10, -10, 10);
 glClearColor(0.5, 0.7, 0.5, 0);
 glutMainLoop();
 return 0;
}