Unity Stochastic Texture Sampling Example

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Oct 14th, 2019

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Shader "Custom/StochasticSample"
{
Properties
{
_Color ("Color", Color) = (1,1,1,1)
_MainTex ("Albedo (RGB)", 2D) = "white" {}
_BumpMap ("BumpMap", 2D) = "bump" {}
_BumpScale ("BumpScale", Float) = 1
_Smoothness ("Smoothness", 2D) = "white" {}
[Toggle]_Stochastic("Stochastic", Float) = 0
}
SubShader
{
Tags { "RenderType"="Opaque" }
LOD 200
CGPROGRAM
// Upgrade NOTE: excluded shader from OpenGL ES 2.0 because it uses non-square matrices
#pragma exclude_renderers gles
// Physically based Standard lighting model, and enable shadows on all light types
#pragma surface surf Standard fullforwardshadows
// Use shader model 3.0 target, to get nicer looking lighting
#pragma target 3.0
fixed4 _Color;
sampler2D _MainTex;
sampler2D _BumpMap;
sampler2D _Smoothness;
uniform float _BumpScale;
uniform float _Stochastic;
struct Input
{
float2 uv_MainTex;
};
// Add instancing support for this shader. You need to check 'Enable Instancing' on materials that use the shader.
// See https://docs.unity3d.com/Manual/GPUInstancing.html for more information about instancing.
// #pragma instancing_options assumeuniformscaling
UNITY_INSTANCING_BUFFER_START(Props)
// put more per-instance properties here
UNITY_INSTANCING_BUFFER_END(Props)
//hash for randomness
float2 hash2D2D (float2 s)
{
//magic numbers
return frac(sin(fmod(float2(dot(s, float2(127.1,311.7)), dot(s, float2(269.5,183.3))), 3.14159))*43758.5453);
}
//stochastic sampling
float4 tex2DStochastic(sampler2D tex, float2 UV)
{
//triangle vertices and blend weights
//BW_vx[0...2].xyz = triangle verts
//BW_vx[3].xy = blend weights (z is unused)
float4x3 BW_vx;
//uv transformed into triangular grid space with UV scaled by approximation of 2*sqrt(3)
float2 skewUV = mul(float2x2 (1.0 , 0.0 , -0.57735027 , 1.15470054), UV * 3.464);
//vertex IDs and barycentric coords
float2 vxID = float2 (floor(skewUV));
float3 barry = float3 (frac(skewUV), 0);
barry.z = 1.0-barry.x-barry.y;
BW_vx = ((barry.z>0) ?
float4x3(float3(vxID, 0), float3(vxID + float2(0, 1), 0), float3(vxID + float2(1, 0), 0), barry.zyx) :
float4x3(float3(vxID + float2 (1, 1), 0), float3(vxID + float2 (1, 0), 0), float3(vxID + float2 (0, 1), 0), float3(-barry.z, 1.0-barry.y, 1.0-barry.x)));
//calculate derivatives to avoid triangular grid artifacts
float2 dx = ddx(UV);
float2 dy = ddy(UV);
//blend samples with calculated weights
return mul(tex2D(tex, UV + hash2D2D(BW_vx[0].xy), dx, dy), BW_vx[3].x) +
mul(tex2D(tex, UV + hash2D2D(BW_vx[1].xy), dx, dy), BW_vx[3].y) +
mul(tex2D(tex, UV + hash2D2D(BW_vx[2].xy), dx, dy), BW_vx[3].z);
}
void surf (Input IN, inout SurfaceOutputStandard o)
{
float4 bumpSample;
float4 albedoSample = 1;
float4 smoothnessSample;
if (_Stochastic)
{
albedoSample = tex2DStochastic(_MainTex, IN.uv_MainTex);
bumpSample = tex2DStochastic(_BumpMap, IN.uv_MainTex);
smoothnessSample = tex2DStochastic(_Smoothness, IN.uv_MainTex);
//etc.
}
else
{
albedoSample = tex2D(_MainTex, IN.uv_MainTex);
bumpSample = tex2D(_BumpMap, IN.uv_MainTex);
smoothnessSample = tex2D(_Smoothness, IN.uv_MainTex);
//etc.
}
o.Alpha = albedoSample.a;
o.Albedo = albedoSample.rgb;
o.Normal = UnpackScaleNormal(bumpSample, _BumpScale);
o.Smoothness = smoothnessSample.r;
//etc.
}
ENDCG
}
FallBack "Diffuse"
}

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