Grass Formation

JasonLavoie

Hey all, I have a quick question.

What's the most effective formation of alpha mapped grass so it doesn't look like complete shit. The camera angle is pretty far away, and the camera can only go so high (for the game), but I'm trying to make the best arrangement for a chunk of grass that can be instanced across a field.

The is for client work so I wanna make the grass model hold up nicely.

Thanks in advance.

Tumerboy

I like the intersecting triangle formation. Think about an anarchy symbol (from above) minus the circle. If you can spare some polys, then you can cut each of the sides down the middle and bend the tops outward which helps to keep them from being noticably cards.

If that doesn't make sense, let me know I can mock it up pretty quick.

odium

Well, waht kind of engine is it? Can you have lit alpha tested stuff? What kind of alpha blending does it have, if any? Can you have large groups of alpha blended polies that draw in the correct order or is it strictly alpha tested only? Can you have sprites and tubes?

The way I have my grass set up in my engine is a little different. We have shadow mapped per pixel lighting (Doom 3 style with shadow maps). Every grass instance is a simple triangle, that points up, but at a slight angle. However we have hundreds of these because we cant use sprites in this idea. We also have to use alpha testing to get the correct lighting info, although we have implemented Alpha To Coverage.

It may be possible for you to do the same, only allow the mesh to rotate on one axis (known as a deform Tube, because it only rotates around the horizontal). That way you dont need as many grass instances, because they look more full (they always face you).

JasonLavoie

Ymerboy: Thanks man, I tried it and it holds up pretty well... but I'm still worried it may not hold up in-gamel... I've been looking at the clients past games and it seems like they just do straight lines.

So what I've done is I've provided them with the 3 vairiations of grass + the anarchy type formation. If it doesn't hold up they can always make custom ones with each piece, or just tell me to make it better :P

odium: Sadly I only know the basic details, the other artist I'm working with has most of the details, so I'll be running it by him first before we go furthur.

Thanks again all, if anyone has any other suggestions then thats great.

Also... I've been looking at Black and White 2... do they use some sort of fur for grass?

Tumerboy

There have been a number of games where Alpha was such a bottleneck, that they just modeled individual blades of grass, and then LODed them out fairly quickly.