3.2.1.1 Grobject

Description. The application structure (APS) of type 'grobject' is used to group graphical primitives in a picture together and assign certain attributes to the group. The object is geometrically identified either by the set of primitives enclosed between the BEGIN APS and END APS elements (if any), or by the spatial region associated with the 'region' APS Attribute (if present). 'Grobject' APSs may contain any CGM graphical content allowed by this profile, and may contain other APS and APS attribute content as defined in section 3.3 (the complete, normative WebCGM content model).

Viewer Behavior. A 'grobject' APS may be selected by the user ("pick"). The viewer shall decide about the pick selection in the following manner:

  1. If the object does not contain a 'region' attribute and contains no a LinkURI attributes no further action is required.
  2. If the object contains at least one 'LinkURI' attribute but no 'region' attribute, a click on non-transparent areas of the graphical elements of the object selects the object. If the object does not contain any graphical primitives no further action is required. If the object contains more than one LinkURI attribute, the user shall be given a choice of which URI to navigate.
  3. If the object contains a 'region' attribute and contains at least one LinkURI attribute, then the 'region' shall be used for selection. If the object contains more than one LinkURI attribute, the user shall be given a choice of which URI to navigate.
  4. If the object contains a 'region' attribute but no LinkURI attributes no further action is required.

It is possible that a user selection ("pick") of a object in a displayed WebCGM picture may not have a single unambiguous result - the cursor location may reside within the geometric extent or 'region' of more than one APS. In such a case, the pick priority is as follows:

  1. If the pick has selected only one APS (and it contains a linkURI), then it is the one which is picked;
  2. If the pick has selected more than one APS (and each contains a linkURI), and the APSs are not nested, then the APS with the highest pick priority is the one whose picking region occurs latest in the picture (see the 'region' APS Attribute for definition of "picking region").
  3. If the pick has selected more than one APS (and each contains a linkURI), and the APSs are nested, the user shall be given a choice of which URI to navigate.

Viewers shall give visual feedback to the user that a successful pick has occurred, and an indication of the particular object (or region) which has been picked. The exact method of feedback is viewer dependent.