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Subject: Re: [cgmo-webcgm] ISSUE(S): Style Attributes


Friday, May 6, 2005, 3:10:44 PM, Lofton wrote:

LH> Hi,

LH> While working on test cases and other stuff, I have come upon some problems
LH> around Style Attributes.  Although I don't have a review assignment per se,
LH> I have written them up here.

LH> References:  The stuff on Style Attributes is found in 5.4, and at 5.7.5
LH> "SetStyleAttr".

LH> -- At 5.7.5, following the table, it says "Note Descriptions of all style
LH> attributes have to be provide. [...]".  The basic descriptions do indeed
LH> follow, so the 1st sentence of the note should be deleted.
I agree.

LH> However, the rest of that paragraph provides information that
LH> should be in the descriptions, but is not.  For example, that
LH> stroke-weight affects line-weight and edge-weight (or in CGM
LH> parlance, "line width" and "edge width".
Ok, what do we do about it? We need a proposal.

LH> -- 5.7.5 "SetStyleAttr".  The description of text-font is "TODO".  What is
LH> this going to be?  A font name (presumably), or a CGM text font index
LH> (awkward)?  Is the font constrained to be amongst those in the CGM Font List?
Is there much use for this? Why would someone bother changing the
actual font of a 'para' or 'subpara'? Could we take this out?

LH> -- 5.4 Style Attributes.  This starts right off talking about style
LH> attributes without a clue as to what they are.  Either the table should be
LH> right here, or there should be an intro paragraph that points to the table
LH> in 5.7.5 setStyleAttr.
This section is the CSS2 inheritance model. I agree that it needs some
wording, and a proposal.

LH> 5.4.1.1, #1, "If the style attribute is assigned a value, use 
LH> it".  Assigned a value where?
Assigned a value onto the APS. (where else?). We should review the
words 'style attribute'... this is not the CSS 'style' attribute we
are talking about.

LH> Not in the CGM, as these are not CGM attribute elements.
It could be. 'visibility' and 'interactivity' are (now) cgm
attributes. The problem is the title of section 5.4 "Style
attributes", it needs to be rename.

LH> So it could only be via SetStyleAttr, and that should be mentioned
LH> (and linked) here.
I don't agree.

LH> (One exception:  visibility is settable via XCF also.)
I think what's confusing is the fact that an introduction is missing.

LH> 5.4.1.1, #3, "The initial value of each property is indicated in the style
LH> attribute's definition."  Oops.  We didn't do this.
We don't need to. #3 will never be reached for the exception of
'visibility' and 'interactivity'. All these style attributes have an
implicit value within the CGM document. The problem with the spec is
that this section doesn't make the distinction between 'visibility'
and 'interactivity' and these other style attributes.

LH> Neither the table in 5.7.5 nor the following style attributes'
LH> descriptions give initial value.  Problem:  what should they be?
LH> If you look at the table and  descriptions, it is clear that
LH> "100%" is appropriate for all except  text-font and visibility.
LH> What should 'text-font' be?  (I think we want "as-in-CGM", as it
LH> is well defined there -- this is sort of the text-font equivalent
LH> of "100%".)  What should 'visibility' be?  3.2.2.9 says "Initial
LH> value: on".
BTW, 'visibility' should be removed from this table.

LH> 5.4.1.1, #3, s/property/style attribute/.  Actually, maybe we ought to
LH> change the terminology to something like "style property"?  That would help
LH> to distance it from the CGM element class, "Attribute elements", which is
LH> usually just shortened to "attributes".
I agree we need to improve the terminology, "style property" work
for me.

I'm starting to think we may need two inheritance models.
One for 'visibility' and 'interactivity' using the 3 current bullets
founds in the spec. And a second one for the other style properties
using only the first two bullets.

LH> 5.4.1.2, "Specified values are resolved to computed values after the
LH> document tree is create[d]; for example relative units ('%') are computed to
LH> absolute values (i.e., RGB color or NVDC)."  There is a conceptual problem
LH> here.  Stroke-weight illustrates it.  Suppose "initial stroke-weight" is
LH> 100%.  Suppose the CGM's line-width is 5 and edge width 10 in a given
LH> APS.  What is the NVDC Computed Value for stroke-weight for that APS?  I
LH> don't know the answer.
We could require the implementations to behave 'as if' two values
where inherited (line-width and edge-width)... But to be honest, I
don't even know what's the difference between the two values?

LH> I suspect, because we don't have a 1-to-1 relationship between
LH> style properties and affected CGM attributes, that we're going to
LH> have some problems with Computed Values. 

LH> 5.4.1.2, 2nd pgph, "When the specified value is not 'inherit', the computed
LH> value of a style attribute is determined as specified by the Computed Value
LH> line in the definition of the property."  Oops.  We didn't do this.  This
LH> is not specified in 5.7.5, neither in the table nor the following 
LH> descriptions.  I don't know what it should be.  We need a proposal.
Dieter proposed that we add 'inherit' as a possible value for
'visibility' and 'interactivity'. I don't think it was proposed for
the other style properties. So again, the problem here, is that we
fail to make the distinction between CGM attributes and style
properties.

LH> 5.4.2, "Each style attribute defines whether it is inherited or 
LH> not."   Oops.  We didn't do this.  Neither the table in 5.7.5 nor the
LH> following style attributes' descriptions give inheritance rules.  We need a
LH> proposal (I don't have time right now to work one up.)  (Exception: we know
LH> about 'visibility' from 3.2.2.9.)
Same comment than above.

LH> Some small editorials:
LH> -----
LH> 5.4.1.3, "...for example:  todo".  We need an example here.

LH> 5.4.1, 2nd sentence, s/attributes/attribute/

LH> 5.4.1.1, 1st sentence, s/attributes/attribute/

LH> 5.4.1.1, #3, s/attributes's/attribute's/

LH> 5.4.1.2, s/create/created/

LH> 5.4.2.1, s/Chapter on inheritance to be done.//  (Presumably, that is 5.4.2
LH> plus 5.4.2.1).

LH> All for now,
LH> -Lofton.

-- 
 Benoit   mailto:benoit@itedo.com



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