Question Shadow acne issues when using shadow atten/shadow mask for toon shader

Hi all,

I've been trying to create a toon shader for our game recently in URP 2022.1.15f1, however, I've been running into issues with shadow acne when it comes to the shadow attenuation as well as sampling the shadow mask.

I've recreated a basic setup for a toon shader that still has the problem. The trouble is, when I multiply the results by the shadow & distance attenuation there is really bad shadow acne occuring, however, when I don't do this the shader no longer receives shadows.

Spoiler: Shadow acne when multiplied with shadow/distance attentuation

If I plug the shadow attenuation into the base colour you can see what is getting remapped to the texture gradient.

Spoiler: Shadow attentuation plugged directly into base colour

When I multiply by the sampled shadow mask instead of the shadow/distance attenuation I still get similar results.

Spoiler: Graph using shadow mask instead of attenuation

While it looks like this fixes it this actually doesn't as this only works when the ramp is split down the middle at a value of 0.5.

If I change it to a smooth gradient for example you can see that the issue is still there, though it is improved slightly. I use a different ramp for different objects if I use a smooth gradient to as seem below to clearly show the issue or a gradient texture with multiple shading bandings it's very clear the issue. I can adjust it slightly using the URP asset shadow settings as well as the depth/normal bias settings but this doesn't fix the issue.

Spoiler: Shadow issues when using smooth gradient

This also occurs on additional light shadows as well.

Spoiler: Shadow acne from additional lights

This is the stripped down code used in the graph example above.

Spoiler: HLSL lighting code

Code (CSharp):

1. #ifndef CUSTOM_LIGHTING_DEMO_INCLUDED
2. #define CUSTOM_LIGHTING_DEMO_INCLUDED
3. #ifdef UNIVERSAL_LIGHTING_INCLUDED
4. #include "Packages/com.unity.render-pipelines.universal/ShaderLibrary/RealtimeLights.hlsl"
5. #include "Packages/com.unity.render-pipelines.universal/ShaderLibrary/Lighting.hlsl"
6. #endif
7. void MainLight_float (float3 WorldPos, out float3 Direction, out float3 Color, out float DistanceAtten, out float ShadowAtten){
8.     #ifdef SHADERGRAPH_PREVIEW
9.         Direction = float3(0.5, 0.5, 0);
10.         Color = 1;
11.         DistanceAtten = 1;
12.         ShadowAtten = 1;
13.     #else
14.         #if SHADOWS_SCREEN
15.             half4 clipPos = TransformWorldToHClip(WorldPos);
16.             half4 shadowCoord = ComputeScreenPos(clipPos);
17.         #else
18.             half4 shadowCoord = TransformWorldToShadowCoord(WorldPos);
19.         #endif
20.         Light mainLight = GetMainLight(shadowCoord);
21.         Direction = mainLight.direction;
22.         Color = mainLight.color;
23.         DistanceAtten = mainLight.distanceAttenuation;
24.         //hadowAtten = mainLight.shadowAttenuation;
25.  
26.     #if !defined(_MAIN_LIGHT_SHADOWS) || defined(_RECEIVE_SHADOWS_OFF)
27.     ShadowAtten = 1.0f;
28.     #endif
29.  
30.     #if SHADOWS_SCREEN
31.     ShadowAtten = SampleScreenSpaceShadowmap(shadowCoord);
32.     #else
33.     ShadowSamplingData shadowSamplingData = GetMainLightShadowSamplingData();
34.     float shadowStrength = GetMainLightShadowStrength();
35.     ShadowAtten = SampleShadowmap(shadowCoord, TEXTURE2D_ARGS(_MainLightShadowmapTexture,
36.     sampler_MainLightShadowmapTexture),
37.     shadowSamplingData, shadowStrength, false);
38.     #endif
39.     #endif
40.  
41. }
42. void Shadowmask_half (float2 lightmapUV, out half4 Shadowmask){
43.     #ifdef SHADERGRAPH_PREVIEW
44.         Shadowmask = half4(1,1,1,1);
45.     #else
46.         OUTPUT_LIGHTMAP_UV(lightmapUV, unity_LightmapST, lightmapUV);
47.         Shadowmask = SAMPLE_SHADOWMASK(lightmapUV);
48.     #endif
49. }
50. #ifndef SHADERGRAPH_PREVIEW
51.     #include "Packages/com.unity.render-pipelines.universal/Editor/ShaderGraph/Includes/ShaderPass.hlsl"
52.     #if (SHADERPASS != SHADERPASS_FORWARD)
53.         #undef REQUIRES_VERTEX_SHADOW_COORD_INTERPOLATOR
54.     #endif
55. #endif
56. void MainLightShadows_float (float3 WorldPos, half4 Shadowmask, out float ShadowAtten){
57.     #ifdef SHADERGRAPH_PREVIEW
58.         ShadowAtten = 1;
59.     #else
60.         float4 shadowCoord = TransformWorldToShadowCoord(WorldPos);
61.         ShadowAtten = MainLightShadow(shadowCoord, WorldPos, Shadowmask, _MainLightOcclusionProbes);
62.     #endif
63. }
64. #endif
65.  

Any help is greatly appreciated! I'm sure I must be missing something but I've search everywhere online and can't find a solution anywhere.

 

Did you find a solution? I have the same problem in 2021.3.10f

 

I've noticed issues similar to that if I try to get the termination between light and shadow to go too far beyond the natural termination you would get from N dot L

 

bump

I'm getting same results as op:

 

Unfortunately, I've still not found a solution so would still love to hear if anyone does make any progress on this issue!

 

https://github.com/Cyanilux/URP_ShaderGraphCustomLighting/blob/main/CustomLighting.hlsl

Maybe this helps? It also has toon shader graph

 

Ah, I was using that as a reference but that still has/doesn't fix the issue

 

I think it's because you have receive shadows on but are also moving the terminator of your toon shadow back behind the apex of the curve too much