register-collecting-blit

Registers a blit to occur when garbage collection starts or ends.

• (register-collecting-blit canvas x y w h on off on-x on-y off-x off-y) -> void
      canvas : canvas% object
      x : real number
      y : real number
      w : non-negative real number
      h : non-negative real number
      on : bitmap% object
      off : bitmap% object
      on-x = 0 : real number
      on-y = 0 : real number
      off-x = 0 : real number
      off-y = 0 : real number

  When garbage collection starts, (send (send canvas get-dc) draw-bitmap-section on on-x on-y x y w h) is called. When garbage collection ends, (send (send canvas get-dc) draw-bitmap-section off off-x off-y x y w h) is called.

  The canvas is registered weakly, so it will be automatically unregistered if the canvas becomes invisible and inaccessible. Multiple registrations can be installed for the same canvas.

  See also unregister-collecting-blit.