From: Dr. Olaf Hoffmann <Dr.O.Hoffmann@gmx.de>

Date: Sun, 9 Jul 2006 13:43:03 +0200

To: www-svg@w3.org

Message-Id: <200607091343.03674.Dr.O.Hoffmann@gmx.de>

Date: Sun, 9 Jul 2006 13:43:03 +0200

To: www-svg@w3.org

Message-Id: <200607091343.03674.Dr.O.Hoffmann@gmx.de>

>> as far as I have seen, there is no special note about >> to-animations in any SVG-specification, but it is always >> mentioned, that one has to look into SMIL. Because >> transform and other attributes animatable with >> animateTransform are additive, simply the special >> rules from SMIL for to-animations are applicable. >> This means, the rule has to be applied for each >> component of the transform matrix - this is the >> only way I could work, I can see and as defined >> in SMIL. This is not difficult, but I think, up to now >> any viewer is wrong with this ;o) >I think the problem, though, with using the components of the underlying >value’s matrix is that there is no canonical way to decompose it. In my >example, the “matrix(2,0,0,2,10,10)” could be decomposed as >“translate(10,10) scale(2)” or “scale(2) translate(5,5)”. Which >translate component would be used as the one to animate from? No, don't even try to decompose matrix to some special other transformations, this might cause even more problems. Don't try to calculate something to be post-multiplied - this will cause even more problems and nonsense (I did this on a sheet of paper and it is only possible, if the initial or final matrix has an inverse, for example scale(2 0) has no inverse). A general way for any situation with a to-animation as the highest priority animation is something like the following (of course it is nowhere mentioned, to animate matrix, but one has to do it in cases like this, as well if there is more than one special transformation in the transform attribute or in general if the initial transformation type does not fit to the final): 1. Expand the value of 'to' into a matrix. For example is scale(a d) = matrix(a 0 0 d 0 0). Lets call the result F. 2. Determination of the underlying value from the initial static attribute value and from underlying lower priority animations, I think, it is called CTM in the specifications. 2.a Expand the value from the transform attribute to a matrix. 2.b Perform any underlying animations of transform, post-multiply it or do whatever is necessary to get it and expand it for the time t to a matrix, lets call it C(t). 3. Do the to-animation as specified by SMIL: The animation function becomes something like f(t) = C(t) + (F - C(t)) * t/d (d is the simple duration, see SMIL for details). f(t) is the matrix, that has to be used as the value of transform at the time t (I think, called the CTM(t)). Of course, it is only necessary to do the calculation separately for the six given components in matrix, but even if it is done with the complete matrix (including the 1 at position 3,3) this will cause no problem, position 3,3 will always be 1 because it is 1 in C(t). I never tried to get f(t) myself, but intuitively I guess, that there will be no ugly surprises, because all initial and final transformations are already constrained to be somehow useful. Excursus: This will avoid problems by trying to post-multiply something to get the desired behaviour. Especially there will be no problems as might be caused by using some nasty things like the inverse matrix from something, not always existing, as for example mentioned in SVG1.2 tiny; 7.7.5 The ref() transform value (hopefully no implementor really will try to calculate the inverse of a matrix, because it will be my first check, if it crashes, if the inverse does not exist, what will happen more often as in SVG1.1, just because with vector-effect it will be possible to create visible one-dimensional structures by scaling down one dimension to zero...). Did anyone already try to implement something, which requires the calculation of the inverse in such case? ;o)Received on Sunday, 9 July 2006 11:41:49 UTC

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