Re[2]: [cgmo-webcgm] SV, CV and CSS2-like inheritance [was: Re[2]: [cgmo-webcgm] Style properties]

[Benoit Bezaire <benoit@itedo.com>]

Got it. So for stroke-weight, the easiest would be to inherit the
specified value and not the computed value.

-- 
 Benoit   mailto:benoit@itedo.com


Wednesday, May 18, 2005, 11:46:28 AM, Lofton wrote:

LH> At 10:27 AM 5/18/2005 -0400, Benoit Bezaire wrote:
>>[...]
>>LH> [Stroke-weight is a property of an APS.  If convert-to-absolute for
>>LH> stroke-weight means that you must convert % to NVDC, this cannot be
>>done at
>>LH> the APS level.
>>Why can't this be done at the APS level?

LH> Example:

LH> BegAps obj1;
LH>     BegApsBody;
LH>     linewidth 10;
LH>     line 0 0 1000 1000
LH>     edgewidth 15;
LH>     intstyle empty;
LH>     rect 100 100 900 900;
LH> EndAps;

LH> First, stroke-weight that is already nvdc is no problem.  E.g., if DOM
LH> applied a stroke-weight style property of 25 to 'obj1' ... no issues there.

LH> Suppose stroke-weight is 100%.  What is the nvdc equivalent of that, at the
LH> BegAps element?  What it means inside the APS, at the level of individual
LH> line and fill primitives, is lw 10 and ew 15.  What can you say is the
LH> equivalent inheritable (single) nvdc value of CV of stroke-weight at the
LH> BegAps element?  (To make that last question more interesting, consider
LH> sub-trees of nested APSs within 'obj1'.)

LH> Suppose DOM sets stroke-width to 50% on obj1.  What is the nvdc equivalent
LH> of that, at the BegAps element?  Etc...

LH> -Lofton.


>>LH>   So the CV of stroke-weight is ill-defined at the APS level,
>>LH> if the CV requires convert-to-absolute.]
>>
>>LH> B.) CSS2 says that Computed Values are inherited.  (CSS3 allows each
>>LH> property to define which type of value is inherited.)
>>
>>LH> Condition A and condition B taken together makes it problematic to apply
>>LH> the CSS2 inheritance model exactly to our style properties inheritance.
>>Why is it problematic?

LH> You cannot have both condition A, plus condition B, plus keep close
LH> alignment with the 3 steps (or 4, or 2) of the CSS2 inheritance model.

LH> -Lofton.


>>
>>LH> If we relax condition B, i.e., if we say that SV is inherited down APS
>>LH> branches (for style properties) instead of CV, as allowed by CSS3, then
>>LH> that inheritance model works.  (But it leaves CV pretty much unused in the
>>LH> model, and doesn't solve the problem of uncomputable CV at the APS level.)
>>
>>LH> If we relax condition A -- i.e., convert-to-absolute happens after CV,
>>LH> e.g., at the Used Value stage -- then CV is the same as SV (except for
>>LH> resolution of the values 'inherit', which we don't allow anyway for style
>>LH> properties.)  And inheritance down APS branches works, CSS2-like.
>>
>>LH> -Lofton.