- From: Dirk Schulze <dschulze@adobe.com>
- Date: Mon, 14 Oct 2013 22:10:07 -0700
- To: "robert@ocallahan.org" <robert@ocallahan.org>
- CC: "public-fx@w3.org" <public-fx@w3.org>

On Oct 15, 2013, at 12:26 AM, Robert O'Callahan <robert@ocallahan.org> wrote: > On Mon, Oct 14, 2013 at 4:58 PM, Dirk Schulze <dschulze@adobe.com> wrote: > SVG defines the bounding box of an object as follows [1]: > > "" > getBBox(): Returns the tight bounding box in current user space (i.e., after application of the ‘transform’attribute, if any) on the geometry of all contained graphics elements > "" > > The question is what is the effect of 3D transforms on the bounding box? I assume that there wouldn't be a big difference. It would still be the tight bounding box of the contained elements after transformations. > > More interesting, what is with a perspective projection matrix? Would it affect the bounding box as well? After all, the perspective projection matrix is not very different from a CSS transform which can have perspective values as well. Therefore, I would assume that all the properties: transform, transform-origin, perspective and perspective-origin have an effect on the object bounding box. > > Right, that seems logical to me too. Great. > > Unfortunately this creates a problem: > 1) Evaluating the 'perspective-origin' of an SVG element requires knowing its SVG bounding box. That is right. > 2) Its SVG bounding box depends on the transformations of its children. Right. And as discussed on the perspective projection matrix as well. > 3) The transformations of its children depend on the 'perspective-origin' of the parent. I do not understand how this would be the case? 'perspective-origin' is like two perspective projection matrices that surround the one specified by the 'perspective' property. Or to be clear: The perspective projection matrix is specified by the 'perspective' and 'perspective-origin' properties. This matrix gets multiplied with the transformation matrix that is specified by the 'transform' and 'transform-origin' properties. You are right that 'transform', 'perspective' and 'perspective-origin' may depend on the objects bounding box (which depends on the transformation and oob of the children). I do not see a requirement of the children to know the 'perspective-origin' of the parent? Also, why would it then just be the 'perspective-origin' and not the 'perspective' as well? From the spec [1]: "" It effectively sets the X and Y position at which the viewer appears to be looking at the children of the element. "" Greetings, Dirk [1] http://dev.w3.org/csswg/css-transforms/#perspective-origin-property > > Any suggestions for resolving this? I don't see any obvious solution :-(. > > Rob > -- > Jtehsauts tshaei dS,o n" Wohfy Mdaon yhoaus eanuttehrotraiitny eovni le atrhtohu gthot sf oirng iyvoeu rs ihnesa.r"t sS?o Whhei csha iids teoa stiheer :p atroa lsyazye,d 'mYaonu,r "sGients uapr,e tfaokreg iyvoeunr, 'm aotr atnod sgaoy ,h o'mGee.t" uTph eann dt hwea lmka'n? gBoutt uIp waanndt wyeonut thoo mken.o w

Received on Tuesday, 15 October 2013 05:10:39 UTC