bitmap-stream

A class of object similar to windows in that you can draw onto it but it is never visible on the screen. Its contents, however, can be copied onto a visible window using copy-stream-area. A bitmap-window (or bitmap-pane) has the functionality of a bitmap-stream hardwired into it, implementing the backing-store for automatically refreshing and redisplaying the window. Bitmap-stream is provided in case you want to manage the drawings stored in memory independently. For an example using bitmap-streams, choose the Help menu | CG Examples and look for Bitmap-streams: custom backing store.

One creates a bitmap-stream by calling open-stream, passing the desired size as the value of page-width and page-height keyword arguments. Below is an example expression that creates a bitmap-stream; the two nil arguments are required due to the two deprecated optional parameters of open-stream.

(open-stream 'bitmap-stream nil nil
  :page-width 600 :page-height 400
  :background-color yellow)

A diagram of window and widget classes is shown in Widget and window classes in cgide.htm.

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This page was not revised from the 8.2 page.
Created 2012.5.30.