Opengl,C++ : Draw Line With Mouse Click

1:  #include <GL/glut.h>  
2:  int ww=600,wh=400;  
3:  int first=0;  
4:  int xi,yi,xf,yf;  
5:  void drawLine(int x1,int y1,int x2,int y2)  
6:  {  
7:       glClear(GL_COLOR_BUFFER_BIT);  
8:       glLineWidth(5.0);  
9:       glBegin(GL_LINES);  
10:            glVertex2i(x1,y1);  
11:            glVertex2i(x2,y2);  
12:       glEnd();  
13:       glFlush();  
14:  }  
15:  void display()  
16:  {  
17:       glClearColor(0.2, 0.4, 0.0, 1.0);  
18:       glColor3f(0.7, 0.4, 0.0);  
19:       glClear(GL_COLOR_BUFFER_BIT);  
20:       glFlush();  
21:  }  
22:  void mouse(int btn,int state,int x,int y)  
23:  {  
24:       if(btn==GLUT_LEFT_BUTTON && state==GLUT_DOWN)  
25:       {  
26:            switch(first)  
27:            {  
28:            case 0:  
29:                 xi=x;  
30:                 yi=wh-y;  
31:                 first=1;  
32:                 break;  
33:            case 1:  
34:                 xf=x;  
35:                 yf=wh-y;  
36:                 drawLine(xi,yi,xf,yf);  
37:                 first=0;  
38:                 break;  
39:            }  
40:       }  
41:  }  
42:  void myinit()  
43:  {  
44:       glViewport(0,0,ww,wh);  
45:       glMatrixMode(GL_PROJECTION);  
46:       glLoadIdentity();  
47:       gluOrtho2D(0.0,(GLdouble)ww,0.0,(GLdouble)wh);  
48:       glMatrixMode(GL_MODELVIEW);  
49:  }  
50:  int main(int argc,char** argv)  
51:  {  
52:       glutInit(&argc,argv);  
53:       glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB);  
54:       glutInitWindowSize(ww,wh);  
55:       glutCreateWindow("Draw Line With Mouse Click");  
56:       glutDisplayFunc(display);  
57:       myinit();  
58:       glutMouseFunc(mouse);  
59:       glutMainLoop();  
60:       return 0;  
61:  }