#include <GL/glut.h>
//#include <stdlib.h>
static int leftFirst = GL_TRUE; //  Initialize alpha blending function. 
static void init(void)
{
  glEnable (GL_BLEND);
  glBlendFunc (GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA); 
  glShadeModel (GL_FLAT);
  glClearColor (0.0, 0.0, 0.0, 0.0);
}
static void drawLeftTriangle(void)
{ 
      // draw yellow triangle on LHS of screen 
     glBegin (GL_TRIANGLES);
     glColor4f(1.0, 1.0, 0.0, 0.75); 
     glVertex3f(0.1, 0.9, 0.0); 
     glVertex3f(0.1, 0.1, 0.0); 
     glVertex3f(0.7, 0.5, 0.0); 
     glEnd();}

static void drawRightTriangle(void)
{ 
       // draw cyan triangle on RHS of screen
      glBegin (GL_TRIANGLES);
      glColor4f(0.0, 1.0, 1.0, 0.75);
      glVertex3f(0.9, 0.9, 0.0); 
      glVertex3f(0.3, 0.5, 0.0); 
      glVertex3f(0.9, 0.1, 0.0);
glEnd();}

void keyboard(unsigned char key, int x, int y)
{ 
    switch (key) 
     {
		case 't':
		case 'T':
			leftFirst = !leftFirst;
			glutPostRedisplay(); 
		break;
		/*case 27: /* Escape key */  // 27 is ascii code for escape key.
			//exit();
		//break;
		default:
		break;   }  }
void display(void)
{ 
	glClear(GL_COLOR_BUFFER_BIT); 
	if (leftFirst)
     {
		drawLeftTriangle();
		drawRightTriangle();
	}
	else 
	{
		drawRightTriangle();
		drawLeftTriangle();
	}
	glFlush(); 
}
void reshape(int w, int h)
{ 
	glViewport(0, 0, (GLsizei) w, (GLsizei) h);
	glMatrixMode(GL_PROJECTION); 
	glLoadIdentity(); 
	if (w <= h)
		gluOrtho2D (0.0, 1.0, 0.0, 1.0*(GLfloat)h/(GLfloat)w);
	else
		gluOrtho2D (0.0, 1.0*(GLfloat)w/(GLfloat)h, 0.0, 1.0);
}

int main(int argc, char** argv)
{ 
	glutInit(&argc, argv);
	glutInitDisplayMode (GLUT_SINGLE | GLUT_RGB);
	glutInitWindowSize (200, 200); 
	glutCreateWindow (argv[0]);
	init();
	glutReshapeFunc (reshape);
	glutKeyboardFunc (keyboard);
	glutDisplayFunc (display);
	glutMainLoop();
	return 0;
}