Mike Williams <mik### [at] econymdemoncouk> wrote:
> Permitting the continuation of a render that was stopped part way
> through would need extra attention. If the render was stopped during the
> AA pass, then the continuation would need to find files containing both
> the result of the first pass and the partial render of the AA pass.

  Not really. It just needs to save the image rendered so far and put some
extra information in the image file (most image formats support this) about
what it was doing before it was interrupted. Basically it just would have
to write the information "I was at the antialiasing pass and was interrupted
at this pixel".

> I guess that there might also be some subtle problems with things like
> isosurface cacheing, particularly if the image has large areas where the
> values don't change enough to cause many extra rays to be cast on the
> second pass.

  I don't see any difference between the current antialiasing scheme and
the second-pass-antialiasing in this respect. They both do the same thing,
but at different times.

> I also suspect that an antialliassing algorithm that really did look in
> all four directions would take longer to render

  I don't see why.

> and produce a result that looks worse (or at least no better)

  I definitely don't see why. If anything, it will look better because it
has more existing information to perform the antialiasing, which may help
it doing a better job.

> With the present algorithm, a vertical or horizontal black/white
> transition results in one pixel being supersampled - the one that has
> the colour transition on its top or left.

  Are you completely sure of this? If you look carefully at what antialiasing
does, it does modify the existing pixels at the left and up of the current
pixel.

> So I would expect this to result in twice the number of
> supersample calculations being performed, and double the width of the
> grey zone, which may well be enough to make the image look out of focus.

  I don't want to sound rude, but that is plain nonsense.

-- 
#macro N(D)#if(D>99)cylinder{M()#local D=div(D,104);M().5,2pigment{rgb M()}}
N(D)#end#end#macro M()<mod(D,13)-6mod(div(D,13)8)-3,10>#end blob{
N(11117333955)N(4254934330)N(3900569407)N(7382340)N(3358)N(970)}//  - Warp -

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