On 18 Apr 2004 10:20:36 -0400, Warp <war### [at] tagpovrayorg> wrote:

>Severi Salminen <sev### [at] not_thissibafi> wrote:
>> I see no clever reason why there is not/should be the center parameter.
>
>  I do.
>
>  AFAIK all primitives are created with no transformation matrix by
>default. The transformation matrix only slows down the raytracing if
>it's unneeded and thus it's not created by default to any primitive.
>For instance, a sphere with a center (located anywhere) and a radius
>can be raytraced without a transformation matrix.
>  Even when you transform a primitive POV-Ray will try to avoid
>creating a transformation matrix if it can. For example, if you
>translate or scale uniformly a sphere (and probably even when
>you rotate it) it will not create a transformation matrix for it
>but only modify its center and radius.
>
>  A torus is a quartic. I don't remember if you can specify a location
>offset for the torus quartic, but whether or not you can, the torus
>implementation was probably designed to be as fast as possible by
>not introducing more complexity to the quartic. Thus any transformation
>you apply to the torus (even a translate) will generate a transformation
>matrix for it. This means that if the torus syntax would have a center
>parameter, a transformation matrix would always be created for it.
>  Granted, this would probably not matter anything, but the torus
>probably just follows the same principle as all the other primitives:
>No transformation matrix by default.
>
>  (And no, I haven't checked if it's true that no primitives get a
>transformation matrix by default, so I may be wrong here. :) )

There's something about this that certainly sounds right.

--------------------------------
My First Subgenius Picture Book:
http://www.imbjr.com

Post a reply to this message