[tom]

this kind of shadow pass is possible with other engines without that white line, so what would they be doing different to get around that?

Brett, it would be very helpful if you could post one of those render and shadow (knocked-out) passes which are matching without gap. Thanks!

[simmsimaging]

Hey Tom -

so I stand (mostly) corrected yet again




I say "mostly" because I think the gap issue is a bit less pronounced in the Vray render, but then again that render is noisy and with more clarity the gap might be much the same (which highlights a different problem with Vray: it can be hard to get clean shadow passes with that one).

I didn't try it with any other engines as I presume it will be the same thing more or less. I guess the next question is this: would it be possible to have a way to include certain objects with the shadow pass, without making them shadow pass *only*? That way they would contribute to that pass and avoid the white line problem, but would be covered by the beauty pass object anyway. That is more or less how I have generally done it in Vray, which might be why I haven't really run into the white line problem before.

/b

[tom]

The thickness of gap is directly related to antialiasing. (In your example above, notice the other engine produced a sharper image by looking at the edge of ground where it meets the background. AA is less, therefore the gap is smaller but it is not a solution.) Imagine you cut out object and shadow without AA from each other. The pixels would match perfectly when they come together. But, antialiasing gives an irreversible damage to this assembly. Because, antialiasing means blending edge pixels with the background. This is why it's not related to the render engine. As I've said, open PS, bring a layer of image, cut a part of it and paste it into a new layer. You will notice those two parts won't come together without a seam anymore. The suggested way of shadow compositing is rendering full shadows instead of knocked-out ones.

[oz42]

This method works http://support.nextlimit.com/display/ma ... ow+channel (see the bit about half way down with the car) but means rendering twice, unfortunately.

[tom]

Yes, it's a full shadow pass.

[eric nixon]

So why not change the way maxwell renders shadow passes to full shadow? and ignore the industry standard which doesnt work...

[tom]

Because, it's much faster to fetch knocked-out shadow information. Full shadow calculation would be more time consuming even if it's not exactly doubling the rendertime. We have plans offering full shadow pass at renderime but keep in mind it may not be remarkably faster than rendering them apart.

[simmsimaging]

I think it would be worth having the option built-in, even if it isn't much (or any faster). It is still easier to set it up and requires less changing to the scene - which makes it far less prone to user error.

The more times I have to turn things off and on the more chance I'm going to make a mistake

/b

[tom]

We agree.