2 sided alpha planes?

Ruz

I was a bit confused about whether you can use single sided aplha planes with shadow volumes. Obviously its a pain in the arse to have for example a hair or grass plane with 2 sides. besided doubling the poly count, its just a pain.
BUT for stencil shadows your meshes cannot have open edges. I am presuming therefore you have to cap all of your alpha planes or the shadow volume will try and close the holes and spray polys all over the place.
anyone got any thoughts on this?

Ghostscape

rendering a poly two sided doubles the polycount anyways.

You can just model them onesided, then duplicate them, flip the normals and change the smoothing group, and then attach and weld.

Depending on the engine you're working with I believe some of them have the ability to ignore alpha'd models to speed things up.

Ruz

yeah I have done this before ie welded/flipped the normals. i was just hopeing that I wouldn't have to it he he.
I am not working with a specific engine bTW, just designing a few assets as if they were for a next gen engine.
you would think that the modern engines would be able to render two sided without me having to do it manually.
what a pain

katzeimsack

When I worked with gamebryo, we had a "doublesided" flag for objects.

JKMakowka

Hmm, but AFAIK wouldn't the alpha still fail to cast a correct shadow with stencil shadows?

EarthQuake

Doubling sided in every engine i've used means they just disable culling, which means the backside will get lit incorrectly. So you have to duplicate it, the other way is just a hack. This would be fine if you had a fullbright texture or something that doesn't get lighting, but if you're using normals its going to look wrong.

Rick Stirling

However sometimes a doublesided flag is much easier to work with - the inside of a skirt for example. Making actual polygons and then skinning them so that they don't intersect is a pain. Since it's inside you don't really need to worry about it not being lit completely correctly.

CrazyButcher

btw jkmakowka brings for a very important note, alphatested stuff will not work with stencil shadows anyway, as volume extraction is done on poly basis, not pixel.

Ruz

So for example , the model i am making here is an office plant, with solid plant pot and big leaves. Would it be wise to have the leaves unlit and alpha test? Currently it has no alpha, but I will be roughing up the edges of the leaves with an alpha map.

EarthQuake

Actually with leaves i've found that it can look better to just turn culling off, leaves will get a good amount of SSS and have light the bounces around in them, so harsh lighting dosent look as good as you would think, atleast in our engine.

Ruz

Rick_Stirling - Thats a good point - generallly if the inside of a skirt is too dark, no one would really notice.

EQ, I will give that a try, cheers.