On 18 Jan 1999 03:58:23 -0500, Nieminen Mika <war### [at] cctutfi> wrote:
>Spider <spi### [at] bahnhofse> wrote:
>: Difference is slowwwww...
>
>  This isn't always true either.

And even when it is true, it's no slower than intersection or merge.
In fact, difference and merge may both be expressed in terms of 
intersections, and within the program differences are indeed expressed 
as intersections.

For the curious:

difference {object {A} object {B}} 
is equivalent to 
intersection {object {A} object {B inverse}}

and

merge {object {A} object {B}} 
is equivalent to
intersection {object {A inverse} object {B inverse} inverse}

(An aside: would making this substitution in the parser simplify the
CSG evaluation code sufficiently to gain any significant performance 
on rendering?  I doubt it.  Currently, in fact, the intersection 
version renders just a tiny bit slower than the merge version for the
same scene.  I don't know why that is.)

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