Ans:

#include <GL/gl.h>
#include <GL/glut.h>
void init(void)
{
glClearColor (1.0, 1.0, 0.0, 0.0);
glShadeModel (GL_SMOOTH);
}
void triangle(void)
{
glBegin (GL_TRIANGLES);
glColor3f (0.0, 1.0, 0.0);
glVertex2f (5.0, 5.0);
glColor3f (0.0, 1.0, 0.0);
glVertex2f (25.0, 5.0);
glColor3f (0.0, 1.0, 0.0);
glVertex2f (5.0, 25.0);
glEnd();
}
void display(void)
{
glClear (GL_COLOR_BUFFER_BIT);
triangle ();
glFlush ();
}
void reshape (int w, int h)
{
glViewport (0, 0, (GLsizei) w, (GLsizei) h);
glMatrixMode (GL_PROJECTION);
glLoadIdentity ();
if (w <= h)
gluOrtho2D (0.0, 30.0, 0.0, 30.0*(GLfloat) h/(GLfloat) w);
else
gluOrtho2D (0.0, 30.0*(GLfloat) w/(GLfloat) h, 0.0, 30.0);
glMatrixMode(GL_MODELVIEW);
}
int main(int argc, char** argv)
{
glutInit(&argc, argv);
glutInitDisplayMode (GLUT_SINGLE | GLUT_RGB);
glutInitWindowSize (500, 500);
glutInitWindowPosition (100, 100);
glutCreateWindow (argv[0]);
init ();
glutDisplayFunc(display);
glutReshapeFunc(reshape);
glutMainLoop();
return 0;
}