Re: [css-transforms][svg11] Effect of perspective and 3D transform on SVG bounding box

On Tue, Oct 15, 2013 at 1:10 AM, Dirk Schulze <dschulze@adobe.com> wrote:

> On Oct 15, 2013, at 12:26 AM, Robert O'Callahan <robert@ocallahan.org>
> wrote:
> > 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.
> ""
>

Yes, it depends on the value of "perspective" as well.

The perspective matrix on the parent affects where the child gets rendered
within the parent. The bounding-box of the parent depends on where the
child gets rendered. Is this unclear?

Rob
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