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Description: this code adds a new output filter to dot/tcldot.
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The new filter is called "imap". It is used just like "ps,"
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"ismap," "gif," and the rest of the output filters.
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The new filter produces an "imap" file, the new-style
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Apache-compatible equivalent of the old-style "ismap" file which
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dot already knows how to produce. In either case, the purpose is
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to map regions or points on a gif image to URLs, so that the user
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of a web browser can click on the gif image and activate anchors
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that invoke other pages. The "ismap" map file style which was
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commonly used with early (NCSA) http servers required an external
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mapping mechanism kept in the cgi-bin dir (ismap executable or
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user-supplied equivalent), whereas recent Apache servers include
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the imap functionality in the server itself. To configure an
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Apache server to use imap files correctly, uncomment this line
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# If you wish to use server-parsed imagemap files, use
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AddHandler imap-file map
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in srm.conf. From then on, you can use files of the form mumble.map
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<A HREF="./EER.Database.map">
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<IMG ISMAP SRC="./EER.Database.gif">
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The .map file will be used as the image map for the associated
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gif image. The new "imapgen" filter for dot produces valid imap
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files for use with Apache servers.
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In addition to being Apache-compliant, the imap file produced
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by imapgen can include clickable edge points as well as node
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rectangles. If the attribute "URL" is defined for an edge, then
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the label virtual node will be bound/mapped to that URL, as will
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spline points along the edge. If the special attributes "tailURL"
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and/or "headURL" are set, then the head and tail points of the
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edge will be bound to those URL, otherwise the head and tail will
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default to the main URL. The older ismapgen code did not
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[JCE may wish to correct my wording in the description of ismap
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(old-style) files above]