ways to change the view in WebCGM

[Lofton Henderson <lofton@rockynet.com>]

All --

In the last telecon, while discussing new panZoom for 2.1, we said this 
action item was needed -- an inventory of how the view within the metafile 
can be changed (and defined) in WebCGM 2.0.

So here it is, as background to any further discussion and definition of 
the details of panZoom.  Comments/corrections welcome....

==============================
1.) <param> sub-elements of <object>
==============================

[1] http://www.w3.org/TR/2007/REC-webcgm20-20070130/WebCGM20-IC.html#webcgm_3_4

When:  This stuff is applied at the initial display of the CGM in the HTML 
page.

1a.) 'viewport' <param> defines a sub-rectangle of VDC Extent.  It is 
*deprecated* in 2.0.  Probably not implemented by anyone.
1b.) 'mapping', 'halign', 'valign' <params> define how viewport (or VDC 
extent) are fit into the width-by-height rectangle of the <object> 
tag.  The default is sensible:  isotropic scaling, centered in whitespace 
in the appropriate direction (if the CGM and the <object> rectangle have 
different aspect ratios.)

==============================
2a) execute <a href='...'> link with object behaviors from HTML
2b) execute a linkuri with object behaviors from CGM
==============================

[2] 
http://www.w3.org/TR/2007/REC-webcgm20-20070130/WebCGM20-IC.html#webcgm_3_1_2_4
[3] 
http://www.w3.org/TR/2007/REC-webcgm20-20070130/WebCGM20-IC.html#webcgm_3_2_2_3
[4] 
http://www.w3.org/TR/2007/REC-webcgm20-20070130/WebCGM20-IC.html#webcgm_3_1_2_2

When 2a:  During an interactive browsing session, explicit user mouse-click 
action on an HTML <a> element whose 'href' contains a WebCGM fragment on 
the IRI -- causes the link to be executed, and any object behaviors to be 
performed.  Establishes the initial view of the CGM.

When 2b:  During an interactive CGM viewing session, explicit user 
mouse-click action on WebCGM APS containing a 'linkuri' ApsAttr [3] whose 
IRI contains a WebCGM fragment, causes the link to be executed, and any 
object behaviors to be performed.  If the link is to a different CGM, then 
it establishes initial view (according to Picture Behaviors and linkuri 
parameters).  Within the same CGM, it establishes a new view.

Note that the following do NOT, in themselves, cause a navigation or change 
of view, although they may define the resulting view when another action 
(2a or 2b) causes navigation:

i.) simple occurrence of a 'linkuri' in a metafile instance does not, 
without user interaction, cause any navigation.
ii.) Similarly, the use of the WebCGMAppStructure DOM interface [5] to edit 
(add or change) the linkuri ApsAttr on an APS does not, in itself, cause 
any navigation, until the user interacts with the APS.
iii.) Similarly, the execution of an XCF containing a <linkuri> element -- 
whether by applyCompanionFile() of the WebCGMPicture interface [6] or by 
the execution of a #xcf(someXCF) fragment [7] -- does not, in itself, cause 
any navigation, until the user interacts with the APS to which the XCF 
attaches the linkuri.
iv.) 'viewcontext' and 'region' -- whether occurring in a metafile, or set 
in DOM or by XCF execution -- do not, in themselves, cause any navigation 
or change of view until the user interacts and causes a linkuri to 
execute.  They may however determine the target view [8] upon execution of 
a 'linkuri' (or HTML 'a' execution).

[5] http://www.w3.org/TR/2007/REC-webcgm20-20070130/WebCGM20-DOM.html#L5095
[6] http://www.w3.org/TR/2007/REC-webcgm20-20070130/WebCGM20-DOM.html#L5070
[7] 
http://www.w3.org/TR/2007/REC-webcgm20-20070130/WebCGM20-IC.html#webcgm_3_1_2_6
[8] 
http://www.w3.org/TR/2007/REC-webcgm20-20070130/WebCGM20-IC.html#target-rectangle

==============================
3.) required pan/zoom controls on viewer
==============================

[9] 
http://www.w3.org/TR/2007/REC-webcgm20-20070130/WebCGM20-IC.html#target-rectangle

When:  At any time, the user may exercise required viewer controls to 
change the view within the currently viewed metafile.

==============================
4.) 'src' parameter on WebCGMMetafile interface
==============================

[10] http://www.w3.org/TR/2007/REC-webcgm20-20070130/WebCGM20-DOM.html#L5044
[11] 
http://www.w3.org/TR/2007/REC-webcgm20-20070130/WebCGM20-DOM.html#webcgmmetafile-src

When:  At any time, use of the DOM to set the 'src' parameter [11] on the 
WebCGMMetafile interface may cause the viewer to open a new metafile, or 
change the view within an already-open metafile, by the execution of a 
fragment with object behaviors [2].

It may also cause the execution of a fragment such as "#xcf(someXCF)", that 
causes execution of an XCF.  But as described in #2 above, this does not in 
itself cause a change of view (although it may define things that affect 
the view when a view-changing action does occur.)

==============================
5.) new panZoom Style Property of 2.1
==============================

Details TBD.

We have agreed on the need.  We have agreed that it is a new Style 
Property.  We have agreed that it should be parameterized by a single NVDC 
rectangle.  We have questioned but not answered about details like fit/fill 
(if the aspect ratio doesn't match the viewer window), interaction with #1 
- #4 above, etc.

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