program shoot_target
      real x_draw(2), y_draw(2)

c plot related setting
      i_dummy=pgopen('/xwin')
      call pgenv(0.0,10.0,0.0,10.0,1,-1)
      call pgsfs(2)

c plot target
      x_target=7
      y_target_min=2
      y_target_max=3
      x_draw(1)=x_target
      x_draw(2)=x_target
      y_draw(1)=y_target_min
      y_draw(2)=y_target_max
      call pgsci(2)      
      call pgline(2,x_draw,y_draw)
      call pgsci(1)

c Input parameters
1003  write(*,*)'Vx=?'
      read(*,*)vx
      write(*,*)'Vy=?'
      read(*,*)vy

c cannon fly
      ax=0
      ay=-9.8 
      y=1
      x=0
      dt=0.00001
      xold=x
      yold=y
      do while (y>0)
        vx=vx+ax*dt
        vy=vy+ay*dt
        x=x+vx*dt
        y=y+vy*dt

        call pgbbuf
        call pgsci(0)
        call pgcirc(xold,yold,0.1)
        call pgsci(1)
        call pgcirc(x,y,0.1)
        call pgpt(1,x-0.11,y,-1)   ! A tail.
        call pgebuf

c check_hit
        if((x>x_target).and.(x<(x_target+0.1)))then
          if((y>y_target_min).and.(y<y_target_max)) goto 1000
        endif

        xold=x
        yold=y
      end do

      goto 1001
1000  call wining_animation(x_target,y_target_min,y_target_max)
1001  continue
      write(*,*)'Play again?(1=Yes,0=No)'
      read(*,*)i_again
      if(i_again==1) goto 1003
      end

      subroutine wining_animation(x_target,y_target_min,y_target_max)
      y_middle=(y_target_min + y_target_max)/2
      d_theta=3.14/1800
      theta=0
      r0=2
      rold=r
      do i=1,20000
        theta=theta+d_theta
        r=r0+sin(theta)
        call pgbbuf
        call pgsci(0)
        call pgcirc(x_target,y_middle,rold)
        call pgsci(3)
        call pgcirc(x_target,y_middle,r)
        call pgebuf
        rold=r
      end do
      end