&Clickable Image Support7

HFRD Hypertext Services - Environment Overview

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6 - Clickable Image Support




B Clickable image support is provided as an integral part of HTTPd Lfunctionality (i.e. it is does not require script execution), and so can be Oquite efficient. It will process both NCSA and CERN configuration formats (in Jthe same file if necessary, although for clarity that should be avoided). +

Digression ... How It Works



L When the image specified in the anchor is clicked upon the browser sends a Mmapping configuration file URL, specified in the HTML anchor, along with the Lpixel coordinate of the click, as a query string, to the HTTPd server. The Oserver interprets region specifications in the configuration file to determine Mwhich region corresponds to the coordinates in the query string. A matching Ispecification's URL, or a default if none match, is then accessed by the Mserver (if local), or sent back to, and then transparently reaccessed by the 7browser (redirected, if a different protocol or host). *

Steps For Using a Clickable Image


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  1. create an image configuration file (see i6.1 - Image Configuration File), mapping pixel coordinates of regions within the image to URLs ,
  2. specify an HTML anchor using an inline 0<IMG...> tag, the HREF= 2specifies the path to the image configuration file#
  3. specify ISMAP in the <IMG...> tag 

    For example:(

      <A HREF="ismap_demo.ismap">2  <IMG SRC="ismap_demo.gif" ISMAP></A>
    
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6.1 - Image Configuration File




G Image configuration is done using a plain-text file containing region Kkeywords specifying image pixel coordinates and associated URLs. Clicking Kwithin these coordinates results in the corresponding URL being returned. FFour keywords defining geometrically shaped series of coordinates are Lprovided, along with a default keyword. These can be supplied in either of 9two formats. The NCSA format may be more commonly used. 

    
  1. NCSA

    

    

    

  2. CERN

    

    


B For online examples of rule usage within configuration files see D6.2 - Examples below. Note that:



hint ...

BTo establish the region keywords and coordinates required for the @configuration file it may be necessary to use a program such as AXV to display the image, then by using the mouse locate Nthe required parts of the image, reading off and noting the coordinate pairs, :and finally using these to compose the configuration file.
 

6.2 - Examples




D Here are two examples, essentially just removed fom their original NCERN environment and placed within HFRD's, with links allowing the respective "configuration files to be viewed.