Decals vs blend light decals ?

[motorsep]

I am wondering if decals can be made using blend lights and if it would be equally fast or faster (performance wise). If blend light decals are possible and practical, are there any limitations compare to regular decals? Thanks!

[Bikerdude]

This sound interesting, got some comparison screenshots..?

[motorsep]

I don't since I haven't even tried it. I just thought maybe TDM team tried it and have an insight.

 

I am interested in this approach is due to flexible and fast workflow - projecting decal on a complex surface is always faster (and should look better) than placing patches and aligning them to the surface.

[SteveL]

Interesting question. Both are methods that let you overlay a coloured texture over another textured surface.

 

I haven't tried it as such, but a few thoughts:

 

Blendlights don't have bump maps and can't be positioned above the surface, so for 3d details like our ivy decals, you want a proper decal.

 

Blendlights can be projected on complicated surfaces. They'll usually draw more tris than a decal, because they will redraw the underlying tris of the complex surface. Decals will draw fewer tris if they are a simplified patch that's been stretched over the top. But to balance that, lit decals will be drawn for each light that hits them whereas blendlights will be drawn only once.

 

I bet the performance difference of either option is negligible.

 

Blendlight colours won't be affected by other nearby lights. Alphatested decals are properly lit. So again for things like ivy, you'd want a traditional decal.

 

To fake an alphatested decal using a blendlight, you'd make your alpha map full black/white and use "blend blend" as your blend mode in the material. To fake an opaque decal, you'd use "blend gl_one, gl_zero".

 

If you try it, I'd bet that the result looks quite different for most things, so which to choose will be obvious. One thing that we use decals for that probably *could* be done well with blendlights is dirt on surfaces.

[motorsep]

Thanks SteveL, I'll give it a spin.

 

Polygon throughput on modern GPUs is very high, so it doesn't really hurt performance on high poly scenes.

 

So basically blendlight decals won't be affected by lighting ? If so, then it's kinda useless I was thinking of decaling maps with grime and dirt using blend lights and it will look out if place if lights won't affect blend light decals.

 

I guess it would be nice to have a special light type that supports normal/spec maps and only lights up a surface with some special flag (like that black light surfaces that are only visible with flagged lights). This way the decal light would not affect surrounding surfaces and the decal would have bump and specular and fit nicely with the environment.

 

On the other hand it would be nice to have some autoprojecting decal entity that projects standard decals on any surface, as if it was a blend light.

[SteveL]

Agreed. We do have the "spectrum" keyword for selective light/surface interactions, but I've never thought of a use for it. Not sure it'd help here either...

 

NB The texture projected from a blendlight won't be lit by other lights, but the surface it "lands on" will still be lit ok. So you might be able to use it for grime. The grime itself won't be lit, but the underlying surface will, so if you apply a dark grime pattern with a blend, it'll darken the surface underneath while preserving the light/shadow variation where it shows through from the underlying surface.