#include <GL/glut.h>

void DrawGLScene() {
  glClearColor(1,1,1,0); glColor3f(0,0,0);
  glClear(GL_COLOR_BUFFER_BIT); glBegin(GL_LINE_STRIP);
  glVertex2f (-0.5, 0.0); glVertex2f (0.5, 0.0);
  glVertex2f (0.0, 0.7);  glVertex2f (-0.5, 0.0);
  glEnd(); glFlush();
}

int main(int argc, char **argv) {
  glutInit(&argc, argv);
  glutCreateWindow("Simple OpenGL Example");
  glutDisplayFunc(DrawGLScene);
  glutMainLoop();
}
// gcc -lglut -o example4 example4.c; ./example4