Soft shadows in URP

2025-10-16 13:51 UTC gpt-5-thinking Open in ChatGPT ↗

I am working in Unity URP and I am creating a an unlit shader in shadergraph to customize my shading. Although I have been able to get the shadowAttenuation, it does not appear to be soft shadows which is what I have set up my diectional light to produce. I wonder why that is. Here is the code in my custom function

void MainLight_float(float3 WorldPos, out float3 Direction, out float3 Color, out float DistanceAtten, out float ShadowAtten) { #if SHADERGRAPH_PREVIEW Direction = float3(0.5, 0.5, 0); Color = 1; DistanceAtten = 1; ShadowAtten = 1; #else #if SHADOWS_SCREEN float4 clipPos = TransformWorldToHClip(WorldPos); float4 shadowCoord = ComputeScreenPos(clipPos); #else float4 shadowCoord = TransformWorldToShadowCoord(WorldPos); #endif Light mainLight = GetMainLight(shadowCoord); Direction = mainLight.direction; Color = mainLight.color; DistanceAtten = mainLight.distanceAttenuation; ShadowSamplingData shadowSamplingData = GetMainLightShadowSamplingData(); float4 shadowParams = GetMainLightShadowParams(); ShadowAtten = SampleShadowmap( TEXTURE2D_ARGS(_MainLightShadowmapTexture, sampler_MainLightShadowmapTexture),shadowCoord,shadowSamplingData,shadowParams,false ); //float shadowStrength = GetMainLightShadowStrength(); //ShadowAtten = SampleShadowmap(shadowCoord, TEXTURE2D_ARGS(_MainLightShadowmapTexture, sampler_MainLightShadowmapTexture), shadowSamplingData, shadowStrength, false); #endif }void MainLight_float(float3 WorldPos, out float3 Direction, out float3 Color, out float DistanceAtten, out float ShadowAtten) { #if SHADERGRAPH_PREVIEW Direction = float3(0.5, 0.5, 0); Color = 1; DistanceAtten = 1; ShadowAtten = 1; #else #if SHADOWS_SCREEN float4 clipPos = TransformWorldToHClip(WorldPos); float4 shadowCoord = ComputeScreenPos(clipPos); #else float4 shadowCoord = TransformWorldToShadowCoord(WorldPos); #endif Light mainLight = GetMainLight(shadowCoord); Direction = mainLight.direction; Color = mainLight.color; DistanceAtten = mainLight.distanceAttenuation; ShadowSamplingData shadowSamplingData = GetMainLightShadowSamplingData(); float4 shadowParams = GetMainLightShadowParams(); ShadowAtten = SampleShadowmap( TEXTURE2D_ARGS(_MainLightShadowmapTexture, sampler_MainLightShadowmapTexture),shadowCoord,shadowSamplingData,shadowParams,false ); //float shadowStrength = GetMainLightShadowStrength(); //ShadowAtten = SampleShadowmap(shadowCoord, TEXTURE2D_ARGS(_MainLightShadowmapTexture, sampler_MainLightShadowmapTexture), shadowSamplingData, shadowStrength, false); #endif }

You’re very close—what’s happening is that you’re bypassing URP’s filtered shadow path, so you only ever see a single hard comparison. In URP, soft shadows come from extra filtering work (PCF/PCSS) that’s compiled behind the _SHADOWS_SOFT keyword and/or done in the screen-space shadow pass. Your function samples the shadow map directly, but unless the correct variant is compiled and you use the right sampling path, you’ll get hard shadows.

Here’s how to fix it.

The short fix (recommended)

Let URP do the heavy lifting and just read the result it already computed (which includes soft filtering and strength):

void MainLight_float(float3 WorldPos,
                     out float3 Direction, out float3 Color,
                     out float DistanceAtten, out float ShadowAtten)
{
#if SHADERGRAPH_PREVIEW
    Direction = float3(0.5, 0.5, 0);
    Color = 1;
    DistanceAtten = 1;
    ShadowAtten = 1;
#else
    float4 shadowCoord;
    #if SHADOWS_SCREEN
        float4 clipPos = TransformWorldToHClip(WorldPos);
        shadowCoord = ComputeScreenPos(clipPos);
    #else
        shadowCoord = TransformWorldToShadowCoord(WorldPos);
    #endif

    Light mainLight = GetMainLight(shadowCoord);   // <- includes soft shadows when available
    Direction = mainLight.direction;
    Color = mainLight.color;
    DistanceAtten = mainLight.distanceAttenuation;
    ShadowAtten = mainLight.shadowAttenuation;     // <- use this instead of manual SampleShadowmap
#endif
}

GetMainLight(shadowCoord) returns a Light whose shadowAttenuation already accounts for:

shadow strength
cascades
soft filtering (when enabled)
screen-space shadows (when that path is active)

If you really want to sample yourself

Then you must follow the same path URP uses:

#if SHADOWS_SCREEN
    // Use the *screen-space* shadow texture when that path is enabled.
    float4 clipPos = TransformWorldToHClip(WorldPos);
    float4 shadowCoord = ComputeScreenPos(clipPos);
    float shadow = SampleScreenSpaceShadowmap(shadowCoord); // filtered in screen-space
#else
    // Use shadowmap sampling with URP’s sampling data and params.
    float4 shadowCoord = TransformWorldToShadowCoord(WorldPos);
    ShadowSamplingData s = GetMainLightShadowSamplingData();
    float4 p = GetMainLightShadowParams();
    float shadow = SampleShadowmap(
        TEXTURE2D_ARGS(_MainLightShadowmapTexture, sampler_MainLightShadowmapTexture),
        shadowCoord, s, p, false);
#endif
ShadowAtten = shadow;

If you go this route, soft shadows will only appear in builds/variants where _SHADOWS_SOFT is compiled. Which leads to…

Make sure the right shader variants exist

Soft shadows are a shader variant thing. You need these enabled so the graph actually compiles the soft versions:

URP Asset / Renderer settings
- Shadows enabled for the Main Light
- Soft Shadows turned on
- (If you’re using transparent objects and want soft shadows there) Screen Space Shadows enabled in the Renderer asset
Shader Graph Target (Graph Inspector → URP)
- Main Light checked
- Cast Shadows / Receive Shadows as needed
  (Shader Graph will add _MAIN_LIGHT_SHADOWS, _MAIN_LIGHT_SHADOWS_CASCADE, and _SHADOWS_SOFT variants when these are on.)
Don’t strip the variants
If you use a custom stripping config or aggressive “Optimize Mesh Data,” make sure the soft shadow variants aren’t removed.

Common gotchas

Sampling the wrong path for the define:
When SHADOWS_SCREEN is defined, don’t sample _MainLightShadowmapTexture—use the screen-space shadow function/texture, or call GetMainLight(...) and take mainLight.shadowAttenuation.
Shadow strength ignored:
SampleShadowmap(...) returns visibility; it doesn’t multiply in light shadow strength. GetMainLight(...) does. If you sample manually, you may need to mix with GetMainLightShadowStrength().
Preview vs. Game:
The Shader Graph preview won’t show soft shadows. Always test in scene/game view.

TL;DR

Change your last lines to:

Light mainLight = GetMainLight(shadowCoord);
ShadowAtten = mainLight.shadowAttenuation;

…and ensure soft shadows + main light shadows are enabled in your URP asset and graph target. That will give you the same soft shadows your directional light is producing.