Grass Normals Issue

heyitsroamer

Hey everyone! I'm new to polycount and still new to Unreal so bear with me!

I'm having some issues matching my grass normals to the normals of my landscape, and all I'm getting is uniform normals everywhere. I have my grass distributed by my landscape master material and the normals of my grass mesh are pointed upwards if that's important? I'm also going for a stylized grass look similar to what's used in the Witness and Fortnite. I appreciate the help!

Grass Material Graph:


Normal Visualization:

Obscura

That is not how you do it. Disable "tangent space normal" in the material properties. It will result in uniform normals though. To actually sample the terrain normals, you need a more advanced shader. But the up vector usually works as it is.

heyitsroamer

Thanks for the quick response Obscura! I already had "tangent space normal" unchecked. How would the more advanced shader look so I can match the same normals as the terrain? I'm trying to get my grass normals to look something like the image below. 

heyitsroamer

Oh wait that's from your post from a couple of years back haha!

Obscura

Remove the transform node from the normal input and simply use (0,0,1) and thats it. I also used some slight fading on the roots. Seeing your texture, a contrasted and inverted y gradient of the texcoord works for that (if you have dithered opacity mask enabled).

You can also blend between the up vector and the original vertex normals of the foliage. The up vector would be used on the bottom of the grass, and the original one on the tips. Use lerp to blend between them. The alpha of the lerp would be the aforementioned y gradient.

heyitsroamer

Unfortunately, I'm still having some issues. I don't think the lerp node is working properly to get the original vertex normals of the foliage, which is why I think the tips are white.  Any solutions you can think of so I can achieve the normals in the image above? I really appreciate your help!

Obscura

Lerp b should be "vertex normals" node. The root fading looks great though. 

heyitsroamer

Oops, my bad. I noticed the value there was 1 which would make it white. However, foliage normals still don't look great. Is there anything else I could do? The landscape grass type has random rotation turned on which I why everything looks mismatched I guess?

Obscura

Yep one more thing. I mention the two sided sign in that article. Try that on the up vector, but now you will need the transform node back as you are in world space, so set it to tangent->world.  Also , showing an actual screenshot of how the foliage looks now instead of the passes, would help.

Also, I went for a full stylistic style in that post, so I did not use such strong normalmap. In fact I didn't use any normalmap, which, I understand that it isn't always possible, depending on what style you are going for. 

I'm referring to this picture:
https://us.v-cdn.net/5021068/uploads/editor/ii/9a1dwh3l3t5i.jpg

If it doesn't work with the transform node, try without it...

heyitsroamer

I really appreciate your help! Still having some issues though. Made those changes. Also for the foliage, I'm trying to go for a style similar to what's used in Fortnite. Still gotta make several foliage variations, but I just want to get the shading right first. I'm also gonna have to recolour the foliage as well to match the grass texture.

Obscura

The transform should be before the lerp. It should be before lerp a.

Obscura

Let me know if it still doesn't work and then I'll mock up some example.

heyitsroamer

Nope, still isn't working. I don't know why the world normals of the grass still look completely off. 

Obscura

Ok hold on

heyitsroamer

I discovered that I had recompute normals checked on the mesh. The normals now look more uniform. but they still don't match the landscape.

Obscura

So this is a very test but a more complex one follows the same principle. I've set the material to not use  tangent space normals, painted some planes which had this material, and I got some nice results by using simple up vector:
result:


Consistent shading on back and front faces...
This is the material:

World normal pass:


I didn't use a foliage asset though, I just dropped the mesh directly into the foliage editor. The 0 spec is not necessary, the result looks the same without that too.

Obscura

Actually,  now I see that your first picture was kinda correct in terms of foliage but the terrain normal seems to be wrong. This purple-ish color is the up direction so your terrain normals were clearly pointing in some weird directions. 

heyitsroamer

Alrighty, I made those quick changes and everything does look better. But is there any way to make the lighting of the foliage match the lighting of the landscape? In the image you can see where there isn't direct sunlight on the ground, the grass is still bright. I really do appreciate all the help and advice you've given!

Obscura

Can you show the base color and normal passes of these 2 images? Now it is probably not the lighting but the colors.

heyitsroamer

There ya go! 

Obscura

Since we are assuming that the terrain has no harsh angle changes, this trick will not work when you have steep slopes on the terrain, but you probably don't want to put foliage there anyways, so it should not really be a problem. If you do, you will need a more complex solution, involving either virtual texturing to access the actual terrain normal, or a solution involving render targets for the same reason. In Unreal Engine, or any raster based renderer, shaders are not aware of their surroundings. They are not really aware of themselves either with the exception of their own point. So technically it is not possible to access the normals of any mesh other than your own, and even that is only accessible at your own location, unless you do either of what I mentioned in this post.

Obscura

Terrain normals are still wrong. We are seeing some y value when its clearly a slight x- and z (see the small gizmo on the bottom right of the viewport). Are you using world aligned textures maybe? 

Obscura

Next step is to show the normal part of the terrain shader I guess.

heyitsroamer

Sounds good! My landscape texture is an auto material achieved by using the WorldAlignedBlend node?

Obscura

What happens when you remove that function. Examine the world normal pass to see if it gets better. The flat or almost flat terrain pixels should show the purple-ish color or some shade of that.

heyitsroamer

That's the only layer I have applied to the landscape at the moment.

heyitsroamer

The grass texture disappears. I have the grass placed by a separate world aligned normal node.

Obscura

Okay then you will need to remove the normal map of the terrain for testing purpose. Once you remove it, you will see that it gets purple so there is something with your normal map, or with the math that you do with the normal of the terrain.

heyitsroamer

Normal map removed.

Obscura

Do you do anything more other than normal maps? Cause if I make a terrain and make some basic hills I get a very different result:

heyitsroamer

Here is what the entire landscape looks like?

Obscura

Alright. I think we somehow missed the whole point of that article. I used edited vertex normals on my meshes. The normals of the grass were made to point upwards. Then it will show the same normal as the terrain even when its a steep slope without any shading trickery.  Sorry for the bullshiting, I'm not really sure how this went into such a wrong direction until now. 

heyitsroamer

Nah don’t worry about it! I already have the normals of the grass mesh pointed upwards. Would I have to export the height map to substance and generate a normal map for that and use that on the grass?  Or would I do that in a different way?

heyitsroamer

I appreciate you bearing with all of this!

Obscura

No need to export heightmap to substance or stuff like that. If you send me an example grass card, ill take a look.

heyitsroamer

Here is what the normals look like:

Obscura

In that case, not plugging anything into the normal input should just work. I should make a similar mesh to make an example.

heyitsroamer

Still doesn't look great.. Anything else you can think of?

Obscura

Can you upload a mesh please, because I just switched to blender a few weeks ago and I don't know how to edit the normals there. It doesn't need to be this mesh, it can be another plane with edited normals. Thanks.

heyitsroamer

I can't upload an fbx or blender project file to the discussion so here's a google drive link for the grass planes:
https://drive.google.com/open?id=1OcPbHVgOgJ79G58SHWMlI0e1gXxzeNAf

You use a normal edit modifier to change the direction of all of the normals. 

Obscura

Its kinda hard to tell from the pixture but I have a punch pf them painted there. Tangent space normal is enabled.

heyitsroamer

Could I see the mesh settings? Maybe its something in there?

Obscura

Obscura

heyitsroamer

I reimported the grass and textures with the changes into a new project, sculpted a landscape and painted grass, everything looks great! But I don't know why it isn't working in the original project file?

Obscura

No idea. Its good that at least it works in another one.

heyitsroamer

Honestly what I think I might do is just migrate all the assets to the new project since everything works there! I really appreciate your help Obscura! 

marpuri

Hi I am new to unreal and I am having same problem with grass I want grass normal in the same direction of the landscape normal but I am stuck any help would be appreciated thanks in advance 

marpuri

Finally I think I found the problem that is the normal (0,0,1) is applied as world space normal but we need to apply it as tangent space normal so we just need to use a transfer node so we can use normal(0,0,1) as tangent space normal

MostHostLA

Hi all (first post here)
I was skimming through this and read a comment about not having access to the normal of the terrain within the grass material.
That may be not be true.

First of, since .18 I have been manually pointing vertex normals up in my grass meshes. This solves most issues and makes for some interesting features.

Second, if you place the grass with the aligned to terrain option, the normal from the terrain is immediately accessible by sampling the objects orientation, which is the z vector.

From docs: "The ObjectOrientation expression outputs the world-space up vector of the object. In other words, the object's local positive z-axis is pointing in this direction."

You could use that as the starting value for the lerp shown above, for instance.
This should get the normals to start with the correct angle from the terrain and drift to their proper value. Similar to what you get when you manipulate the vertex orientation in a DCC before import...