program main
  use sgl
  implicit none
  external display ! 聲明display是個(gè)函數(shù)
  ! 設(shè)定當(dāng)窗口需要重繪時(shí),會(huì)調(diào)用子程序display
  call sglDisplaySub(display)  
  ! 打開(kāi)窗口, 窗口左上角為(100,100), 長(zhǎng)寬同為500
  call sglCreateWindow(100,100,500,500,0)
  write(*,*) "Waiting message."
  ! 等待使用者給程序的信息
  call sglMainLoop()
  write(*,*) "The End."
  stop
end
! 每當(dāng)窗口需要更新畫(huà)面時(shí), 會(huì)調(diào)用display
subroutine display()
  use sgl
  implicit none
  call sglClearBuffer()          ! 消除屏幕
  call sglColor3f(1.0,0.0,0.0)   ! 設(shè)定目前要使用紅色來(lái)繪圖
  call sglDrawLine(0,0, 500,500) ! 在(0,0)到(500,500)兩點(diǎn)之間畫(huà)線
  return
end subroutine