backface lighting

Oniram

is there any way to have a mesh with no backface cast a shadow? ive got a bunch of wall pieces that are meant for an interior, and light just goes right through them. a small fix ive got for that is to just build up a BSP wall around the inside of the walls.. but thats a bit tedious. any suggestions?

Xendance

Make the material of the walls two sided?

Legend286

Enable the double sided switch in the material, it should work.

cholden

Unless you're just goofin' around making some art, avoid the 2-sided fix, and either fill with bsp or give those pieces a backface for shadow casting. Everything being 2-sided unnecessarily makes your materials more expensive.

Legend286

cholden wrote: »

Unless you're just goofin' around making some art, avoid the 2-sided fix, and either fill with bsp or give those pieces a backface for shadow casting. Everything being 2-sided unnecessarily makes your materials more expensive.

It's actually better not to add a backface in the modelling program, doing it through the shader culls it if it's not visible anyway, so you don't need to worry about performance loss.

Froyok

Legend286 wrote: »

It's actually better not to add a backface in the modelling program, doing it through the shader culls it if it's not visible anyway, so you don't need to worry about performance loss.

Are you sure of that ?
It's better to have a two-sided shader than more faces on a mesh ? For the GPU it's not too much hard ?

Ben Apuna

I believe that a two sided shader is more expensive than actual geometry.

Two sided shader turns OFF backface culling forcing the GPU to render all triangles (might even be 2 draw calls...).

Actual geometry backfaces get culled by default resulting in less triangles drawn.

So as cholden says avoid the two sided material hack like the plague.

EDIT:

On a side note, why are so many people trying this two sided material thing lately? Is it being taught somewhere as a good way to do things?

one post and another from the Terrible Advice/Myth Thread.

Oniram

yea my original intention was adding geometry or bsps. i knew that the two sided materials were way too expensive for this scene (given that the master material for everything is already kinda expensive). so yea, i guess ill do the geometry thing. thx

and just to add my input to the whole argument.. ive NEVER found geometry to be an issue in UDK. for the most part since ive seen the FoliageMap that has just simple rubble pieces over 4k, i figured that UDK can handle geometry pretty well (which it does), and ive never concerned myself with geometry since. all my lag/gpu issues come into play with materials and/or lighting.

sprunghunt

I have generally found the lighting caluculations on the backfaces of a two sided material to not be very reliable in any engine. You'll often get weirdly dark or strangely bright backfaces.

Ben Apuna

Yeah me too, I used to make double sided materials for foliage in the past.

The lighting/normal calculations were reversed on the backsides and it really made things look strange.

That was back with UE3 though and not with UDK/lightmass maybe it has been "fixed"?

Even then though double sided is probably not good for performance reasons.