Coster-Graphics

Unity Shader Graph Procedural Planet Tutorial

Map 3D Simplex noise to a sphere,
Generate planet terrains by using the noise for vertex displacement,
Map textures to the terrain based on the height of the terrain,
Use a gradient and noise to map different textures to different biomes,
Add different noise settings for each biome,
Add different noise types to choose for each biome with enums.

0. Introduction

Welcome!!!!

In this tutorial we will create a procedural planet shader using Unity’s node-based shader creation tool Shader Graph.
By using home-made custom function nodes we will be able to neatly map 3D Simplex and Cellular noise to the surface of a sphere and use it to create cool random (coloured) noise patterns:

We will use the noise to displace the vertices of the (high-poly) sphere to generate terrain on top of the sphere:

We will also use the noise to blend between multiple terrain textures to make it look instantly game-ee:

We will generate different biomes using noise to sample a gradient, for both the textures and the displacement of the terrain:

And we will also use the biome gradient to generate different noise settings and noise types for each biome!:

By doing this tutorial you will learn:

• How to map 3D Simplex noise to a sphere.
• How to generate terrain on a sphere with noise.
• How to use vertex displacement.
• How to blend textures over the height of the terrain.
• How to create a noise gradient to map different textures to different biomes.
• How to blend two gradients together so that we can overcome the max 8 gradient key limitation.
• How to implement different noise settings for each biome.
• How to implement different noise types for each biome.

There is a lot to cover, many properties to balance, nodes to connect and textures to find, if we want to have a lot of variety, so for that reason the steps are going to be big and the explanations kinda brief,.. But we’re gonna get ‘er done, boys ‘n girls!!….Wicked..

This tutorial was written using Unity 2019.4.9f1 LTS using the URP (Universal Render Pipeline) but should also work with the HDRP and with Unity 2020.x.x and later releases.

0.1 Tutorial Materials

CubeSphere

Because this shader uses vertex displacement to generate terrain height on a sphere we cannot use the default Unity sphere since it doesn’t have a high enough poly count to show detailed enough terrain…
Because UV-Spheres have most of the vertices around the poles it is better to use a so called CubeSphere (a subdivided and then ‘spherized’ cube mesh) for this shader because CubeSpheres have a much more even distribution of vertices, giving us a much more uniform looking displacement.
You can create a CubeSphere in Blender or any other 3D modelling application yourself (Make sure it is smooth shaded) or you can download the one used for this tutorial from the links down below:

For the .fbx mesh Unity doesn’t have to convert the units so make sure Convert Units is unchecked in the import settings.

Custom Nodes

Because Shader Graph doesn’t have a three-dimensional noise node by default this shader uses custom Simplex3D and later Cellular3D noise nodes. (After importing the custom nodes into your project you can find them in the Shader Graph nodes creation menu under Custom/Procedural/Noise):

Textures

The textures used for this tutorial were mostly downloaded from the Unity Asset Store. For cartoony/hand drawn-looking textures you can search the Asset Store or the internet for ‘stylized’ or ‘hand-painted’ textures. Also make sure that the textures are all tile-able/seamless.

I personally really like the stylized textures made by LOWPOLY: https://assetstore.unity.com/publishers/16677

1.0 Mapping 3D Simplex Noise to a Sphere

This Shader Graph uses the vertex Position in object space as input for the position of the simplex noise and then uses the noise for vertex displacement.
To map a coloured gradient to the displacement we can sample the gradient with the Length of the Position but because the Length of the Position without any displacement is already 1 (with a sphere that has a radius of 1), we subtract it from the length first before sampling the gradient. Then we divide it by the Displacement Amplitude to evenly distribute the gradient over the height of the displacement:

If you want the Main Preview window to show the planet correctly make sure to right-click on the Main Preview window and select the custom high-resolution CubeSphere mesh!

2.0 Texture Mapping

Instead of sampling a colour gradient we Lerp from texture to texture over the height of the displacement/Length of the vertex Position, blending textures based on displacement height.
To control where the textures start and end we can use different black & white gradients. The first gradient has a black key on 17.5% and a white key on 22.5%, leaving 5% for the blending in between.
The second gradient has black on 37.5% and white on 42.5% and so on..:

Using gradients like this is great because it makes it visually very clear what is happening. The downside is that we cannot expose gradients so in step 2.2 we’ll switch to using SmoothStep nodes instead…

2.1 Adding normal maps

We can use exactly the same method for mapping Albedo textures to the planet for normal maps (and the same method could also be applied to Metallic, Smoothness and Occlusion maps):

Make sure to set the Type of the Sample Texture 2D nodes to Normal and also set the normal map texture properties Mode to Bump on the BlackBoard:

2.2 Texture Blend Start/End and Noise Power properties

We can use SmoothStep nodes instead of gradients for the texture blending and we can use a Power node instead of a gradient to control the steepness of the displacement. This way we can use exposed Vector2 properties for the start and end of the texture blending and an exposed Vector1 for the Noise Power.
Not only do we give the user of the shader control over those properties this way, we can also decide what the values should be on a per-material basis without having to create multiple shader graph variants, which is cool if we’re going to procedurally generate different planets later on!:

3.0 Adding detail to the terrain with layered noise

To get a more detailed noise and terrain we can use layered noise instead of single noise.
The Layered Simplex3D node uses the same noise function as the non-layered Simplex3D node but instead of sampling the noise function directly the Layered Simplex3D node uses an Evaluate function that samples the noise multiple times in a loop, multiplying the frequency and amplitude of the layer with each iteration:

float4 EvaluateLayeredNoise(float3 p, float3 offset, float strength, int octaves, float baseRoughness, float roughness, float persistence){
    float4 noiseVector = 0.0;
    float frequency = baseRoughness;
    float amplitude  = 1.0;

    for(int i=0; i<octaves; i++){
        float4 n = snoise_grad(p * frequency + offset);
        noiseVector += (n+1.0) * 0.5 * amplitude;
        frequency *= roughness;
        amplitude *= persistence;
    }
    return noiseVector * strength;
}

So Layered Simplex3D noise is basically the same noise layered multiple times with each layer/octave adding more detail to the overall noise structure. This way we can have shapes with smaller shapes with even smaller shapes, for example: Octave 1 could be mountains, octave two large boulders and octave three small rocks.
The amount of layers the noise generates is controlled by the amount of Octaves, the Base Roughness controls the base scale of the noise, the roughness controls the scale of the successive layers added and the Persistence how much each octave contributes to the overall structure of the noise map:

Keep in mind that very detailed noise also need a very high resolution mesh to show properly. It’s no use to have very detailed noise with many octaves if the mesh is not very high resolution, so it is important to find a balance!

4.0 Generating biomes with noise and gradients

To create biomes for our planet we can use the separate RGB channels of a gradient that we sample over the y-axis of the Position for three different biomes. We can use Red for the north and south pole, Green for forest and Blue for desert biomes.
We could sample the gradient with the y-Position directly but then we would get biomes with straight horizontal edges. To make the biomes and the transitions from biome to biome more random looking we can use noise and multiply the y-Position by it before sampling the biome gradient.
To control how rough the biome edges are and to control the noise sampling position we can use properties to scale and offset the biome gradient noise, much in the same way that we did for the terrain noise:

When we have the biome gradient ready we can Split the output into it’s separate RGB components and Multiply the textures from the first biome with the Red channel, the textures from the second biome with the Green channel and the textures from the third biome with the Blue channel. Then we just add them all up.
The same method also applies to the normal maps:

The complete graph now looks like this:

As you can see all three biomes use their own separate textures and normal maps so new Texture, Normal map, Texture Tiling, Texture Offset and Texture Blend Start/End properties have to be added to the blackboard for the two new biomes. The properties of the already existing biome have to be renamed.

Every texture in the graph uses its own texture sampler/Sample Texture 2D node but there is a limit of 16 texture samplers that we can use at once. There are two ways around this limitation, by using Texture2D Arrays (which would have to be created by scripting) or by using a Sampler State.
By connecting a Sampler State property node to multiple texture samplers in the graph we’re basically telling Unity to use the same texture sampler instance for all the textures that are being sampled with samplers that use the same Sampler State:

New textures have to be found for the polar and desert biomes as well. Each biome can use 5 different textures but we can use some of the same textures as we use for the forest biome as well. For the polar biome the example shader uses a blue ice texture and it uses a snow texture a couple of times. The desert uses a rippled sand texture plus the dirt and sand textures from the forest biome.

4.1 Double Biome Gradient

Because we are limited to 8 keys per gradient it is not really possible to generate more than four biome zones on the planet and still have short transitions between them, which is ok if we only needed four zones but it would be nicer if we could have five zones, for example two polar biomes, two forest biomes and one desert biome in the centre.
To get past the 8 key limit we can use two gradients, one for the top half of the planet and the other for the bottom half:

If we setup both the gradients with keys on exactly the same positions but opposite then we can still use a high Biomes Edge Noise Strength to get nice random biome regions without visual artefacts:

To debug the biome gradient, temporarily plug it into the Color input of an Unlit Master node and right-click on it to set it active:

5.0 Biome Noise Settings

Now that we have different textures for each biome it makes a lot of sense to add different noise properties for each biome as well!

To generate noise with different settings for each biome we start with the vertex displacement function at the top, which is going to be for the polar biome only. We Multiply the displacement by the R channel of the Biome gradient with a Split node before the adding of the vertex Position:

Now we have to create new noise and vertex displacement functions with new separate properties for the other two biomes as well,..
The vertex displacement for the forest biome is multiplied by the G channel of the biome gradient. (Notice that we don’t need to add the Position twice):

The Vertex Displacement for the desert biome is multiplied by the B channel of the biome gradient:

To blend the three biome displacement functions we can simply Add them together:

To make the textures for the forest and desert biomes separate displacement functions work, make sure to divide the length by Forest Biome Displacement Amplitude for the forest biome textures and by Desert Biome Displacement Amplitude for the desert biome textures:

Because we have separate noise and displacement functions for each biome now we also have to take that into account for the Occlusion so we have to create two new Occlusion functions and blend the three together in the same way as with the textures and normal maps:

The complete graph with different noise settings for each biome now looks like this:

6.0 Multiple Biome Noise Types

Cool!! Our planets are really starting to look like something now but wouldn’t it be great to have some completely different noise types that we can pick for each biome? I think it would!.. By using exposed Enum Keywords we can switch between different noise nodes in our graph:

(At the time of writing this the enum keyword functionality of Shader Graph is kind of buggy, sometimes it works and sometimes it doesn’t so use this at your own risk.. I’ve found that sometimes after creating an enum it would work until I changed a reference name or reference suffix from one of the enum entries so it might take a couple of retries before it works. My advice for when you want to use enums is to keep the default reference name and refference suffix names and to not use too many Enum Keywords because there is a limit to how many shader variants Unity can create.
Also sometimes is helps to disconnect and reconnect the enum nodes after changing stuff or to completely recreate the enum keyword property on the blackboard..)

For the example I’ve chosen to use the F2 minus the F1 noise value of Cellular 3D noise because I like that it looks like cracked ground or ice but there are many different ways to use Cellular or Simplex noise for different Biome Noise Types… So experiment with it!:

The complete graph with different noise types for each biome: