!  Plotting routine of equi-streamline in colors
   parameter (nx=200,ny=100)
    call init
      call viewport(0.2,0.2,0.8,0.5)
      call xyworld(0.0,0.0,2.0,1.0)
      call frame
      call draw(1.0,-1.0,20)
      call frame
    call fin
  stop
  end
!
  subroutine frame
  integer :: nx=4,ny=2,ix,iy
  real(4) :: dx=0.05, dy=0.05
      call linewidth(1.0)
      call rect(0.0,0.0,2.0,1.0,0.0,1.0,1)
      do  ix=0,2*nx-1
        call setgray(0.0)
        x=float(ix)/float(nx)*2.0
        dy=0.05
        call plot(x,0.0,3)
        call plot(x,dy,2)
        call stroke()
      end do
      do iy=0,ny-1
        call setgray(0.0)
        y=float(iy)/float(ny)
        dx=0.05
        call plot(0.0,y,3)
        call plot(dx,y,2)
        call stroke()
      end do
      call textx(1.5,0.0,1,'x')
      call textx(0.0,0.02,1,'0')
      call textx(1.0,0.02,1,'1')
      call textx(2.0,0.02,1,'2')
      call texty(0.0,0.75,1,'y')
      call texty(0.0,0.0,1,'0')
      call texty(0.0,0.5,3,'0.5')
      call texty(0.0,1.0,1,'1')
 return
 end
 function f(x,y)
        real(4) :: pi=3.14159,x,y,f
        f=sin(2.0*pi*x)*sin(pi*y)
 return
 end
 subroutine draw(fmax,fmin,nline)
   integer :: nx=200,ny=100,ix,iy
   real(4) :: dx,dy,x,y,r,g,b
      dx=2.0/float(nx)
      dy=1.0/float(ny)
      do iy=1,ny
       y=float(iy)/float(ny)
       do ix=1,nx
        x=float(ix)/float(nx)
          color=(f(x,y)-fmin)/(fmax-fmin)
	  call plot((ix-1)*dx,(iy-1)*dy,3)
	  call plot(ix*dx,(iy-1)*dy,2)
	  call plot(ix*dx,iy*dy,2)
	  call plot((ix-1)*dx,iy*dy,2)
	  call closepath
          r=color*0.8+0.2
          g=0.1
          b=(1.0-color)*0.8+0.2
          call setrgb(r,g,b)
          call fill
          call stroke
       end do
     end do
  return
  end