just a couple of quick comments, hopefully not betraying my biases too obviously.
1. it seems that this would be at least a partial reversion of the work that was very recently done in rev 12594. Before rev 12594, the conversion from arc to Bezier was done in sp-ellipse.cpp using a formula that appears to be identical to the one being used in rev 12833 of the proposed branch inkscape/elliptical_arc. This bypassed the sbasis representation entirely, afaict. After rev 12594, the arc form was kept as long as possible, the explicit conversion from arc to Bezier is no longer performed, and is instead done indirectly through sbasis. (The sbasis conversion from arc to Bezier in lib2geom is, I think, closely equivalent to the result obtained before rev 12594.) The purpose of this change in rev 12594, I assume, was to postpone the conversion to Bezier as long as possible, which I would agree with in principle. In Inkscape 0.48.4, if you do a Path->Object to Path operation on a circle, you get a Bezier, which is both lossy and unnecessary. In current trunk, this does not happen.
2. there is an undesirable practical side effect of rev 12594, however: namely it is not clear how many Beziers will actually be produced from an arc. There are two reasons for this. First, the formula that determines the error in the fit appears to be unnecessarily pessimistic as discussed previously: http://inkscape.13.x6.nabble.com/Recent-change-to-ellipse-to-path-conversion...
3. second, the number of Beziers you get from an arc depends on the size of the object, which seems unexpected, given that svg is a scalable format. imho it would be preferable to have a dimensionless measure of the goodness of fit, independent of the size of the object. This would need to be done in the routine build_from_sbasis() in sbasis-to-bezier.cpp. The problem of course would be in defining what the size of the object is, which can be difficult, witness the case of filters where some properties of filters are in dimensionless units while other properties are in absolute units, leading to confusion when the shape changes drastically.
cheers, Alvin
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