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Subject: resolutions about geometric transform
- From: Lofton Henderson <lofton@rockynet.com>
- To: cgmo-webcgm@lists.oasis-open.org
- Date: Wed, 20 Feb 2008 09:56:09 -0700
All --
Here is my summary of how the technical issues about geometric transform
have been resolved. See "SOURCES" below for more
references supporting this summary.
Please comment immediately if you think any of this is inaccurate, or if
any critical details are omitted.
SUMMARY:
1.) available via: method on DOM interface(s), plus XCF;
2.) They replace the *specified* transform associated with the target
object (which defaults to Identity);
3.) When a transform is set or specified on a target node, it composes
with transforms on ancestor nodes in the object tree like SVG [3], and
this composition results in the effective CTM on the node that is
targeted by the transform-setting method (or XCF);
4.) When a transform is set or specified on a target node, it composes
with transforms on descendent nodes in the object tree like SVG [3], and
this composition updates the effective CTM on those nodes;
[3]
http://www.w3.org/TR/SVG11/coords.html#NestedTransformations
5.) we would like them to be parameterized both as a single matrix (six
numbers needed [2]), or as convenience components (scale, rotate,
translate, ...)
6.) we agree that they should have an associated parameter, with values
'replace' or 'combine' (or some such values) that control whether the
method replaces the current modally defined transform on the target node,
or combines with it. (In either case, then CTMs are recomputed as
per #3 and #4 -- the effect of the parameter concerns the modally-defined
*specified* value of the transform for the node, not the CTM)
7.) We call them Style Properties, but they don't 'inherit' like the
model of 5.4; they compose/combine as per #3 and #4.
8.) Accordingly, per today's telecon, for simplicity and clarity we
should put them in methods of their own, setTransformSP() and
getTransformSP().
9.) The methods would be defined on the ????? interface? The
current Style Property methods are on the Picture and APS
interfaces. ("Picture" has been questioned for the new
geometric transform SP.)
10.) CGM:1999 (hence WebCGM) contains controls that determine how
transforms affect line width, patterns, etc. Nothing more need be
specified for the new 'transform' SP.
SOURCES: The thread [0] contains some precise detail, about exactly
what is meant by composition of transforms up and down the object tree,
how replace/combine works, etc. There is also information in thread
[1] about the mathematics, where 'transform' is defined, etc.
[0]
http://lists.oasis-open.org/archives/cgmo-webcgm/200801/msg00078.html
[1]
http://lists.oasis-open.org/archives/cgmo-webcgm/200801/msg00001.html
[2]
http://www.w3.org/TR/SVG11/coords.html#TransformAttribute
Regards,
-Lofton.
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