register-collecting-blit in Global Graphics and Screen

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. If canvas's device context has a scale, the scale may or may not be temporarily disabled during the bitmap drawing.

  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.