Line drawing with mouse click event in OpenGl

#include <GL/glut.h> 
int ww = 600, wh = 400;
int first = 0;
int xi, yi, xf, yf;
void drawLine(int x1, int y1, int x2, int y2)
{
glClear(GL_COLOR_BUFFER_BIT);
glLineWidth(5.0);
glBegin(GL_LINES);
glVertex2i(x1, y1);
glVertex2i(x2, y2);
glEnd();
glFlush();
}
void display()
{
glClearColor(1.0, 1.0, 0.0, 1.0);
glColor3f(1.0, 0.0, 0.0);
glClear(GL_COLOR_BUFFER_BIT);
glFlush();
}
void mouse(int btn, int state, int x, int y)
{
if(btn==GLUT_LEFT_BUTTON && state == GLUT_DOWN)
{
switch(first)
{
case 0:
xi = x;
yi = (wh-y);
first = 1;
break;
case 1:
xf = x;
yf = (wh-y);
drawLine(xi,yi,xf,yf);
first = 0;
break;
}
}
}
void myinit()
{
glViewport(0,0,ww,wh);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
gluOrtho2D(0.0,(GLdouble)ww,0.0,(GLdouble)wh);
glMatrixMode(GL_MODELVIEW);
}
int main(int argc, char** argv)
{
glutInit(&argc,argv);
glutInitDisplayMode (GLUT_SINGLE | GLUT_RGB);
glutInitWindowSize(ww,wh);
glutCreateWindow("demo");
glutDisplayFunc(display);
myinit();
glutMouseFunc(mouse);
glutMainLoop();
return 0;
}