From: Cyril Concolato <cyril.concolato@telecom-paristech.fr>

Date: Fri, 01 Jun 2012 08:39:21 +0200

Message-ID: <4FC86399.4090503@telecom-paristech.fr>

To: www-svg@w3.org

Date: Fri, 01 Jun 2012 08:39:21 +0200

Message-ID: <4FC86399.4090503@telecom-paristech.fr>

To: www-svg@w3.org

Le 5/31/2012 10:35 PM, Cyril Concolato a écrit : > Hi Dirk, > > See my comment inline. > > ----- Mail original ----- > De: "Dirk Schulze"<dschulze@adobe.com> > À: "SVG public list"<www-svg@w3.org>, public-fx@w3.org > Envoyé: Samedi 26 Mai 2012 18:56:27 > Objet: [css3-transforms] neutral element for addition - by animation > > Hi SVG folks, > > I have a question to by animations on transforms. See the simple example here: > > <rect width="100" height="100"> > <animateTransform attributeName="transform" attributeType="XML" > type="scale" by="1" dur="5s" fill="freeze"/> > </rect> > > This example scales from 0 to 1, since the neutral element for scale is 0. This is relevant because of the definition in SMIL Animation: > > "" > Normative: A by animation with a by value vb is equivalent to the same animation with a values list with 2 values, the neutral element for addition for the domain of the target attribute (denoted 0) and vb, andadditive="sum". Any other specification of the additive attribute in a by animation is ignored. > "" [1] > > [CC] Adding 1 in the scale transformation means going from scale(X) to scale(X+1), therefore the neutral element is scale(0) which is the identity matrix. I made a mistake. I meant to say scale(1) is the identity matrix. This does not change my conclusion. scale(X+0)=scale(X)scale(1)=scale(X) Cyril > > > And according to SVG animation, the animated transform gets post multiplied to the userspace transform of the element (which is the identity matrix). > > My question is the following: Every transform function (independent if translate, scale or rotate) is just a shorthand for the underlaying transformation matrix (3x3/(3x2) or 4x4). Therefore, shouldn't the neutral element for addition on every transform function be the null matrix? If that is the case, what happens for the following example: > > <rect width="100" height="100"> > <animateTransform attributeName="transform" attributeType="XML" > type="translate" by="100,100" dur="5s" fill="freeze"/> > </rect> > > Shouldn't the neutral element here be the zero matrix? > [CC] No. Adding 100,100 to a translate means going from translate(tx,ty) to translate(tx+100,ty+100), therefore the neutral element is translate(0) which is also the identity matrix. > > And shouldn't it mean that at the beginning of the animation the userspace transform gets post multiplied by this null matrix and therefore the element gets invisible? And as a consequence, shouldn't the element scale from 0 to 1 and translate from 0 to 100 at the same time? > [CC] No. > > Non of the tested implementations scale the rect for the second example. I think this is incorrect from the mathematical point of view. > [CC] No, I think they interpret it as I indicated. > > Of course it is also possible to define the neutral element for every single transform function. But then the null element doesn't really make sense for me. > [CC] The neutral element is the identity matrix for transformation 'addition' (i.e. composition). It works for scale, rotate, translate, skew ... > > Cyril > > > I prefixed the subject with [css3-transforms] since I want to specify it in CSS3 transforms and believe that the current definition is incorrect [2]. > > Greetings, > Dirk > > [1] http://www.w3.org/TR/SMIL3/smil-animation.html#q34 > [2] http://dev.w3.org/csswg/css3-transforms/#neutral-element >Received on Friday, 1 June 2012 06:39:56 UTC

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