Water Caustics Shader

Water Caustics Shader implemented with Shader Graph in Unity 2021.3.10f1

Screenshots

7.mp4

Table of Content

• Scene Setup
• HLSL
  • Main Light
  • UV Rotation
  • Triplanar Projection
• Shader Graph
  • Caustics Tiling and Speed
  • Caustics Texture Rotation
  • Caustics Distortion
  • Caustics Distorted Triplanar
  • Caustics End Result
  • Additive Caustics
  • Oclussion
    • Oclussion Screenshots
  • Global Illumination
  • Complete Graph

Resources

• Jettelly Caustics Tutorial 1
• Jettelly Caustics Tutorial 2
• Caustics Texture
• Stylized Skybox
• Custom Lighting in Shader Graph
• Triplanar ShaderGraph Node HLSL code
• UV Rotation ShaderGraph Node HLSL code

Scene Setup

• Built a basic pool and put some primitive objects inside.
• Used the stlylized skybox to make the scene look more polished.

HLSL

Main Light

• Based on the example for implementing custom lighting in Shader Graph, we define the custom HLSL function to get the main light.
• SHADERGRAPH_PREVIEW will be true while developing the shader in the Shader Graph node editor.

void MainLight_half(
    in float3 WorldPos,
    out half3 Direction,
    out half3 Color,
    out half DistanceAtten,
    out half ShadowAtten
)
{
    #if SHADERGRAPH_PREVIEW
        Direction = half3(0.5, 0.5, 0);
        Color = 1;
        DistanceAtten = 1;
        ShadowAtten = 1;
    #else
        #if SHADOWS_SCREEN
            half4 clipPos = TransformWorldToHClip(WorldPos);
            half4 shadowCoord = ComputeScreenPos(clipPos);
        #else
            half4 shadowCoord = TransformWorldToShadowCoord(WorldPos);
        #endif

        Light mainLight = GetMainLight(shadowCoord);
        Direction = mainLight.direction;
        Color = mainLight.color;
        DistanceAtten = mainLight.distanceAttenuation;
        ShadowAtten = mainLight.shadowAttenuation;
    #endif
}

UV Rotation

• Simply a copy paste of the HLSL code from the documentation for the Shader Graph Node to do UV roation.

float2 Unity_Rotate_Degrees_float(float2 UV, float2 Center, float Rotation)
{
    Rotation = Rotation * (3.1415926f/180.0f);
    UV -= Center;

    float s = sin(Rotation);
    float c = cos(Rotation);

    float2x2 rMatrix = float2x2(c, -s, s, c);

    rMatrix *= 0.5;
    rMatrix += 0.5;
    rMatrix = rMatrix * 2 - 1;

    UV.xy = mul(UV.xy, rMatrix);
    UV += Center;

    return UV;
}

Triplanar Projection

• Based on the HLSL code from the Shader Graph Node to do Triplanar Projection.
• The modifications for this include passing in a Speed and Rotation for the UVs.
• The offset will be calculated with Time and Speed.
• The rotation will be used with the previously defined HLSL function.
• This returns a projection based on the world position of the vertices, using each plane as an UV mapping.
  • This means the projection will always be the same, no matter the shape or position of the object.
  • There will be a blending done using the Normals orientation and a blend parameter.

void TriplanarProjection_float(
    in Texture2D Texture,
    in SamplerState Sampler,
    in float3 Position,         // world space
    in float3 Normal,           // world space
    in float Tile,
    in float Blend,

    // UV manipulation
    in float Speed,
    in float Rotation,

    out float4 Out
)
{
    float3 Node_UV = Position * Tile;

    // animate UVs
    float Offset_UV = _Time.y * Speed;

    float3 Node_Blend = pow(abs(Normal), Blend);
    Node_Blend /= dot(Node_Blend, 1.0);

    float4 Node_X = SAMPLE_TEXTURE2D(Texture, Sampler, Unity_Rotate_Degrees_float(Node_UV.zy, 0, Rotation) + Offset_UV);
    float4 Node_Y = SAMPLE_TEXTURE2D(Texture, Sampler, Unity_Rotate_Degrees_float(Node_UV.xz, 0, Rotation) + Offset_UV);
    float4 Node_Z = SAMPLE_TEXTURE2D(Texture, Sampler, Unity_Rotate_Degrees_float(Node_UV.xy, 0, Rotation) + Offset_UV);

    Out = Node_X * Node_Blend.x + Node_Y * Node_Blend.y + Node_Z * Node_Blend.z;
}

Shader Graph

Caustics Tiling and Speed

• Define a Custom Function Node using the Triplanar Projection we defined in HLSL.
• Set a Caustics Texture, a Tiling and a Speed for the Offset of the UVs.

Caustics Texture Rotation

• Make one of the Caustic Textures rotated by the amount determined by Caustic Texture Rotation.

Caustics Distortion

• Use the Caustics Distortion Speed multiplied by Time, to offset a Vector2 composed by the RG channels of the World Position of the vertices.

• Divide by Caustics Distortion Factor, to further modify the distortion.

• Use Caustics Distortion Scale to control the scale of the noise.

5.mp4

Caustics Distorted Triplanar

• Use the distorted World Position of the vertices as input to sample the Triplanar Projection.

Caustics End Result

• The end result simulates the caustics of the water surface, but a much lower computational cost.

1.mp4

Additive Caustics

• Add the caustics color to a primary Texture, to overlay on top of whatever color the object has.

6.mp4

Oclussion

• Use a Custom Function Node to execute the MainLight HLSL function we wrote earlier.
• Get the Direction, Color, Distance Attenuation and Shadow Attenuation for the main light.
• Calculate a simple Lambert shading using the dot product of the light direction and the Normal Vector.
• Multiply the Distance and Shadow Attenuations by the Color of the light.
• Multiply everything together to calculate a colorized oclussion mask for the caustics.

Oclussion Screenshots

• Using different angles of light.

8.mp4

Global Illumination

• Use the Baked GI Node to access the Ambient/Global Illumination from the Scene.
• Multiply it by the Albedo color coming from the Main Texture.

10.mp4

Complete Graph

• Multiply the Oclussion by the Caustics to mask it out.
• Multiply the Ocluded Caustics by the Albedo + Global Illumination.