W3C home > Mailing lists > Public > public-svg-wg@w3.org > October to December 2008

Re: ISSUE-2129 (definition clarifications): Definition section is too long and needs clarifications (bbox, canvas, etc.) [Last Call: SVG 1.2 Tiny ]

From: Doug Schepers <schepers@w3.org>
Date: Wed, 15 Oct 2008 16:56:15 -0400
Message-ID: <48F658EF.1080200@w3.org>
To: anthony.grasso@cisra.canon.com.au
CC: cyril.concolato@telecom-paristech.fr, SVG Working Group WG <public-svg-wg@w3.org>

Hi, Guys-

Nice work on moving the description of bbox to Coords, Anthony.  I have
one nit, inlin below...

Anthony Grasso wrote (on 10/15/08 10:34 AM):
> 
>>>   This definition says:
>>> "For curved shapes, the bounding box must enclose all portions of the
>>> shape along the edge, not just end points, but must not include
>>> control points for curves that are not within the shape itself."
>>> The 'must not' requirement should be changed to a 'should' because
>>> depending on the curve and depending on the precision of the
>>> implementation (fixed point), it may be impossible to make a bounding
>>> box that does not include the control point. 
>> There was actually a mistake in my comment. The proposed edit is replace:
>> "For curved shapes, the bounding box must enclose all portions of the
>> shape along the edge, not just end points, but must not include
>> control points for curves that are not within the shape itself."
>> with
>> "For curved shapes, the bounding box must enclose all portions of the
>> shape along the edge, not just end points, but should not include
>> control points for curves that are not within the shape itself."
>>
> 
> As per your suggestion the "must not" was changed to "should not". I
> added an additional sentence at the end to help clarify the paragraph:
> "For example, control points of a curve that are at a further distance
> than the curve edge, from the non-enclosing side of the curve edge, must
> be excluded from the bounding box."
> 
> Do you think this sentence helps with clarification of the paragraph?

The passage was indeed ambiguously worded, previously.  However, I
thought the new wording was also a bit unclear... the "should not"
wording could be read to indicate that implementations are permitted to
include control points in the bbox if there is a good reason for them to
do so, such as performance.  In fact, the exclusion of control point
must remain a must, but the passage needed qualifying remarks.  I've
changed it as below [1], and retained Anthony's f'rinstance:

[[
For curved shapes, the bounding box must enclose all portions of the
shape along the edge, not just end points. Note that control points for
a curve which are not defined as lying along the line of the resulting
curve (e.g., the second coordinate pair of a Cubic B├ęzier command) must
not contribute to the dimensions of the bounding box (though those
points may fall within the area of the bounding box, if they lie within
the shape itself, or along or close to the curve). For example, control
points of a curve that are at a further distance than the curve edge,
from the non-enclosing side of the curve edge, must be excluded from the
bounding box.
]]

[1] http://dev.w3.org/SVG/profiles/1.2T/publish/coords.html#BoundingBox

Regards-
-Doug
Received on Wednesday, 15 October 2008 20:56:28 GMT

This archive was generated by hypermail 2.2.0+W3C-0.50 : Wednesday, 15 October 2008 20:56:29 GMT