How to make Decent grass planes

Guy123

Hello All

I've decided to dust off the old game art skills and get to making a new environment. However whenever making grass planes, they always end up looking rubbish!

I've got a picture here, that I want to make a bush out of. Can anyone give me any advice as to the best way to create decent looking grass planes?



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If there are any tutorials you reckon I should look at please link me!

commander_keen

If your talking about how to actually render them so they look like grass instead of planes the key is to manipulate the vertex normals. Simply pointing them in a somewhat upward direction can help a lot but ideally you would also want to do something more fancy with shaders like diffusing the normals so they have less crisp lighting. Something like half lambert:
[/imagetheft]

Ben Apuna

It depends a little on what software you are using to create the grass in and what app you will be displaying your final environment it.

Generally I would model and texture a single blade grass, then use whatever modeling tools I have available to modify that original grass blade to produce some bent and broken variants.

Then you form a clump out of many instances of the grass blades you created earlier, then use render to texture just like on any other high poly to low poly bake to get a, diffuse, normal, and alpha texture.

An cool technique you can do in UDK and any other engine that supports custom vertex normals is to make all of the vertex normals of your in game grass planes point straight up. That way the shading between the ground and the grass planes get averaged and it makes the transition between the two much less visible.

There are a bunch of threads about this subject and foliage in general around here that you might want to check out. Try the wiki too.

I hope that helps.

l.croxton

http://www.jamesshaw.co.nz/blog/?p=400

Is that something you are after?

Guy123

Hey Guys thanks for the replies!

@Croxton, Thanks, that was interesting, I will have to look at it in more detail when i get back from work but I think it could be an avenue worth investigating. I always thought it was best just t simply cut the alpha out of a photo.

I'm using Photoshop and putting it into UDK.

The reason I asked what the best way of making it was that it was taking me aaaagggeeeesss to cut the grass out of the photo as an alpha. And while I am definitely up for putting hard work into it and realise that there is no magic 'make this awesome' button, I couldn't help but think that there might be a quicker way of doing it.

From what I have read a lot of people use render to texture and physically model the grass strands. This might have to be something I consider. My only concern is that the grass I have been trying to alpha is very thin, and physically modelling the blades would be likely to make them appear larger than in reality.

Does anyone know of the way most game artists make alphas from photographs? Should I re-shoot the photos against a black bit of card?

Mark Dygert

Guy123 wrote: »

Does anyone know of the way most game artists make alphas from photographs? Should I re-shoot the photos against a black bit of card?

Grass? It's not worth the time and headache to make it useable. Even if you blue screen it. The diffuse coloring isn't all that complex so you aren't saving any time there. So then its the arrangement of the grass that you're trying to save and at that point you can randomly generate the same patterns pretty quickly.

Hair and fur comes to mind, which would be surprising if no one mentioned it already (haven't read every link in the thread yet). It's a prefect grass clump simulator.

Create 3 splines like this, start from the bottom, the vertex number is important.
Then apply hair/fur and adjust the parameters.

Then go back and tweak the spline (toggle on/off show end result in the modifier stack list) to create the desired shape.

You can adjust the color of the strands at the bottom and the top to help generate a gradient that shows age and shadowing.

You can take those splines, copy them, apply a surface modifier and now have low poly card geometry, UV map it, and bake.

You can also go back down to the spline and refine the lines, adding points to create more graceful bends or use the "create line" tool to make more splines.

You can also use several different copies of the hair/fur to get different results such as tall sprigs of grass in the center and smaller shorter grass around the bottom.

You can control the density of the strands, the thickness at the bottom and the top as well as specular and gloss values, these can be rendered out to spec/gloss maps as well.

You can also hook up dynamics like wind and render out animated frames if the game/engine support it.


But so much is dependent on unanswered questions:
The scene, are these all over a huge area or one tuft in a small courtyard?
The game, is this going to be used anywhere else?
The hardware its running on, does it favor alpha test opacity maps, how about if they're stacked 50 deep, or intersecting so you have a plane that is half behind and half in front?
How is it going to be lit, does it need to cast accurate dynamic shadows or is the lighting diffused enough that you can fake it with vertex colors, light maps or diffuse tricks?
How important is it,