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Unity Engine

Use shadows in a custom URP shader

Get shadow data from lights in the scene, and calculate shadows.
Read time 3 minutesLast updated 22 days ago
To use shadows in a custom Universal Render Pipeline (URP) shader, follow these steps:
  1. Add 
    #include "Packages/com.unity.render-pipelines.universal/ShaderLibrary/Lighting.hlsl"
    inside the 
    HLSLPROGRAM
    in your shader file. The 
    Core.hlsl
    file imports the 
    Shadows.hlsl
    and 
    RealtimeLights.hlsl
    files.
  2. Use any of the methods from the following sections.

Get a position in shadow space

Use these methods to convert positions to shadow map positions.

Method

Syntax

Description

GetShadowCoord
float4 GetShadowCoord(VertexPositionInputs vertexInputs)
Converts a vertex position into shadow space. Refer to Transform positions in a custom URP shader for information on the 
VertexPositionInputs
struct.
TransformWorldToShadowCoord
float4 TransformWorldToShadowCoord(float3 positionInWorldSpace)
Converts a position in world space to shadow space.

Calculate shadows

The following methods calculate shadows using shadow maps. To use these methods, follow these steps first:
  1. Make sure there are objects in your scene that have a 
    ShadowCaster
    shader pass, for example objects that use the 
    Universal Render Pipeline/Lit
    shader.
  2. Add 
    #pragma multi_compile _ _MAIN_LIGHT_SHADOWS _MAIN_LIGHT_SHADOWS_CASCADE _MAIN_LIGHT_SHADOWS_SCREEN
    to your shader, so it can access the shadow map for the main light.
  3. Add 
    #pragma multi_compile _ _ADDITIONAL_LIGHT_SHADOWS
    to your shader, so it can access the shadow maps for additional lights.

Method

Syntax

Description

GetMainLight
Light GetMainLight(float4 shadowCoordinates)
Returns the main light in the scene, with a 
shadowAttenuation
value based on whether the position at the shadow coordinates is in shadow.
ComputeCascadeIndex
half ComputeCascadeIndex(float3 positionInWorldSpace)
Returns the index of the shadow cascade at the position in world space. Refer to Shadow cascades for more information.
MainLightRealtimeShadow
half MainLightRealtimeShadow(float4 shadowCoordinates)
Returns the shadow value from the main shadow map at the coordinates. Refer to Shadow mapping for more information.
AdditionalLightRealtimeShadow
half AdditionalLightRealtimeShadow(int lightIndex, float3 positionInWorldSpace)
Returns the shadow value from the additional light shadow map at the position in world space.
GetMainLightShadowFade
half GetMainLightShadowFade(float3 positionInWorldSpace)
Returns the amount to fade the shadow from the main light, based on the distance between the position and the camera.
GetAdditionalLightShadowFade
half GetAdditionalLightShadowFade(float3 positionInWorldSpace)
Returns the amount to fade the shadow from additional lights, based on the distance between the position and the camera.
ApplyShadowBias
float3 ApplyShadowBias(float3 positionInWorldSpace, float3 normalWS, float3 lightDirection)
Adds shadow bias to the position in world space. Refer to Shadow troubleshooting for more information.

Example

This code example is a simplified example of drawing shadows onto a surface. It might not work correctly with more than one shadow cascade.
To generate shadows, make sure there are objects in your scene that have a 
ShadowCaster
shader pass, for example objects that use the 
Universal Render Pipeline/Lit
shader.
Shader "Custom/SimpleShadows"{    SubShader    {        Tags { "RenderType" = "AlphaTest" "RenderPipeline" = "UniversalPipeline" }        Pass        {            HLSLPROGRAM            #pragma vertex vert            #pragma fragment frag            #pragma multi_compile _ _MAIN_LIGHT_SHADOWS _MAIN_LIGHT_SHADOWS_CASCADE _MAIN_LIGHT_SHADOWS_SCREEN            #include "Packages/com.unity.render-pipelines.universal/ShaderLibrary/Lighting.hlsl"            struct Attributes            {                float4 positionOS  : POSITION;            };            struct Varyings            {                float4 positionCS  : SV_POSITION;                float4 shadowCoords : TEXCOORD3;            };            Varyings vert(Attributes IN)            {                Varyings OUT;                OUT.positionCS = TransformObjectToHClip(IN.positionOS.xyz);                // Get the VertexPositionInputs for the vertex position                  VertexPositionInputs positions = GetVertexPositionInputs(IN.positionOS.xyz);                // Convert the vertex position to a position on the shadow map                float4 shadowCoordinates = GetShadowCoord(positions);                // Pass the shadow coordinates to the fragment shader                OUT.shadowCoords = shadowCoordinates;                return OUT;            }            half4 frag(Varyings IN) : SV_Target            {                // Get the value from the shadow map at the shadow coordinates                half shadowAmount = MainLightRealtimeShadow(IN.shadowCoords);                // Set the fragment color to the shadow value                return shadowAmount;            }                        ENDHLSL        }    }}

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