Conditional Backdrops

version 2/110428 by Mike Ciul

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    This is a simple extension to allow rules for determining whether a backdrop is present in a particular room. Although moving backdrops has been possible within I7 since version 5T18, it must be done with a description of objects that doesn't refer to the backdrop being moved (at least as of 6G60). This quirk prevented a single rulebook from controlling the location of multiple backdrops. Conditional Backdrops avoids the problem by creating a new kind governed by a special rulebook.

    The "conditional backdrop" kind is governed by the "backdrop condition" rulebook. By default, a conditional backdrop will not be present in any room. This can be changed by adding backdrop condition rules for the object. Such a rule should conclude with the one of the phrases "it is present" or "it is absent" to make a decision.

    A conditional backdrop is not a kind of backdrop, and so it can't be moved by the rules that apply only to backdrops. Only the "backdrop condition" rulebook may be used.

        The sky is a conditional backdrop.
        A backdrop condition for the sky: if the location is the yard, it is present.

    Note: Backdrops are only automatically updated at certain times (such as when moving from one room to another). If a backdrop condition can change under other circumstances, this must be updated manually by invoking the "move floating objects rule" or by directly calling the phrase "update backdrop positions."

    Conditional Backdrops was originally written by John Clemens before there was any provision for moving backdrops in I7, and this update merely allows the extension to work with version 6G60. If you have any questions, suggestions or bug reports, you may send them to Mike Ciul at