- From: Dirk Schulze <dschulze@adobe.com>
- Date: Sat, 21 Apr 2012 06:55:18 -0700
- To: "Dr. Olaf Hoffmann" <Dr.O.Hoffmann@gmx.de>
- CC: "www-style@w3.org" <www-style@w3.org>, "public-fx@w3.org" <public-fx@w3.org>

Hi Olaf, On Apr 21, 2012, at 6:40 AM, Dr. Olaf Hoffmann wrote: > Hello, > > this is about: > http://www.w3.org/TR/2012/WD-css3-transforms-20120403/#mathematical-description > > The draft shows some examples, what can be assumed as the effect of several > types of transformations and in this chapter 17. it provides a 'Mathematical > Description of Transform Functions' - well, better it provides only matrices, > no direct relation to the effect of such a matrix on the presentation. > > For 2D-Transforms it is sufficiently described in SVG already what the > effect for a point r = (x, y, 1) for a matrix M is, r_p representation in the > previous coordinate system, r_c in the current coordinate system > (respectively r=(x, y, z, ?) for three dimensions?): > > r_p = M r_c A bug report [1] on W3C also points out that we should be more clear and adapt more from SVG 1.1[2] as well as SVG Transform [3]. And I agree. > > > I think this should be noted in this draft as well - and this is even more > important for the matrices related to 3D-transformations, because it is not > obvious, what the relation is. > The old SVG transform draft http://www.w3.org/TR/SVG-Transforms/ > has slightly more advanced descriptions. Well, even with these formulas > I do not get something similar to for example 5 of the current draft. I agree that SVG Transforms is more descriptive, but also slightly different from CSS3 Transforms. > > Due to my experience with perspective transforms, for a central projection, > what seems to be intended here in examples like 4,5, one needs an > additional transformation like (index _p here for projected) > > (x_p, y_p) = (x_c, y_c) * l/z_c with l a length. > > Obviously the fourth dimension of the matrices is intended for this, > but the relation to such a transformation is not decribed. > > The parallel projection as intended in example 3 is simpler, > one just has to use a simple 3x2 (respectively 4x2) matrix, to > extract only the x and y components. > > > > > > I suggest to decribe/define the effect of such matrices > in detail as a functional relation between the representation of an arbitrary > point r_c in the current coordinate system to the representation of > this projected point r_p. > Other solutions for the problem are possible as well of course, but > without a precise description at least the effect of the 3D transforms > are undefined and those of the 2D transforms are applicable only for SVG, > that has already a precise description for 2D. > > > Best wishes > > Olaf > > > > > PS: Is it really useful to change the preferred mailing list for this draft > to the www-style list instead of the public-fx, as for the previous draft? > Because the draft applies still to SVG as well, I added the public-fx… > Mails should always go to public-fx. I am not sure why this changed in the ED. Greetings, Dirk [1] https://www.w3.org/Bugs/Public/show_bug.cgi?id=15605 [2] http://www.w3.org/TR/SVG/coords.html [3] http://www.w3.org/TR/SVG-Transforms/

Received on Saturday, 21 April 2012 13:55:49 UTC