- From: Jasper van de Gronde <th.v.d.gronde@hccnet.nl>
- Date: Wed, 29 Aug 2012 19:16:54 +0200
- To: www-svg@w3.org

On 29-08-12 15:53, Erik Dahlstrom wrote: > On Wed, 29 Aug 2012 14:20:28 +0200, Dr. Olaf Hoffmann > <Dr.O.Hoffmann@gmx.de> wrote: > ... >> What could be the intended effect for a negative 'fr'? > > Not sure, I don't think we allow circles to have a negative radius > anywhere else in svg. > >> Define, that the absolute value has to be used, if there is no intended >> effect known. >> This is better as to disallow, because if the viewer fixes this, the >> authors >> cannot fail by accident anymore ;o) > > I agree. If you take the absolute value before interpolating, then you get the weird situation that a cone (for example) first gets "thinner" and then thicker again as you change the radius of one end from positive to negative. It would make more sense to have a logical progression, where at fr=0 you get a cone that ends/starts in a point, and for fr<0 you essentially get a "double cone". This is also the typical picture you have when defining a circle as one of the conic sections: http://en.wikipedia.org/wiki/Conic_section It also makes perfect sense if you represent a circle by x^2+y^2=r^2, or using a parametric representation. I uploaded some images of what this would look like: http://home.hccnet.nl/th.v.d.gronde/negativeRadius/tube.png http://home.hccnet.nl/th.v.d.gronde/negativeRadius/cone.png http://home.hccnet.nl/th.v.d.gronde/negativeRadius/double%20cone.png The first goes from radius 5 to radius 5, the second from 5 to 0 and the last from 5 to -5. The images were drawn by solving (x-cx(t))^2+(y-cy(t))^2-r(t)^2 and taking the largest t within the interval [0,1], blending the colour between red and blue.

Received on Wednesday, 29 August 2012 17:17:25 UTC