void drawPolyLineFile(char * fileName)
{
	fstream inStream;
	inStream.open(fileName, ios ::in);	// open the file
	if(inStream.fail())
		return;
	glClear(GL_COLOR_BUFFER_BIT);      // clear the screen 
	GLint numpolys, numLines, x ,y;
	inStream >> numpolys;		           // read the number of polylines
	for(int j = 0; j < numpolys; j++)  // read each polyline
	{
		inStream >> numLines;
		glBegin(GL_LINE_STRIP);	     // draw the next polyline
		for (int i = 0; i < numLines; i++)
		{
			inStream >> x >> y;        // read the next x, y pair
			glVertex2i(x, y);
		}
		glEnd();
	}
	glFlush();
	inStream.close();
}