When Character Animator executes a program, the program might need to use the terminal for input and output. If you only have access to a single terminal, and both Character Animator and the executing program need access to it, Character Animator keeps a virtual image of the program's output in the background. This image is displayed, and Character Animator swapped to the background, when you press F2=View, or if Character Animator itself displays the program's output (during Step or Zoom operations, for example).
By default, the size of this virtual screen is set to 24 lines. You can change this by setting the environment variable LINES before starting Character Animator; for example:
export LINES=40 anim program.int
You should not set LINES to a size greater than the actual depth of the screen.
For detailed information on environment variables, see Environment Variables.