Emulator Issues #11626
openFeature Request - MSAA for Alpha Testing via Alpha to Coverage
0%
Description
The following post by Ben Golus details how to Use MSAA to antialias alpha testing by assigning different alpha cut off thresholds for different coverage samples
https://medium.com/@bgolus/anti-aliased-alpha-test-the-esoteric-alpha-to-coverage-8b177335ae4f
Here is his final Unity Implementation:
Shader "Custom/Alpha To Coverage"
{
Properties
{
_MainTex ("Texture", 2D) = "white" {}
_Cutoff ("Alpha cutoff", Range(0.15,0.85)) = 0.4
_MipScale ("Mip Level Alpha Scale", Range(0,1)) = 0.25
}
SubShader
{
Tags { "RenderQueue"="AlphaTest" "RenderType"="TransparentCutout" }
Cull Off
Pass
{
Tags { "LightMode"="ForwardBase" }
AlphaToMask On
CGPROGRAM
#pragma vertex vert
#pragma fragment frag
#include "UnityCG.cginc"
#include "Lighting.cginc"
struct appdata
{
float4 vertex : POSITION;
float2 uv : TEXCOORD0;
half3 normal : NORMAL;
};
struct v2f
{
float4 pos : SV_POSITION;
float2 uv : TEXCOORD0;
half3 worldNormal : NORMAL;
};
sampler2D _MainTex;
float4 _MainTex_ST;
float4 _MainTex_TexelSize;
fixed _Cutoff;
half _MipScale;
float CalcMipLevel(float2 texture_coord)
{
float2 dx = ddx(texture_coord);
float2 dy = ddy(texture_coord);
float delta_max_sqr = max(dot(dx, dx), dot(dy, dy));
return max(0.0, 0.5 * log2(delta_max_sqr));
}
v2f vert (appdata v)
{
v2f o;
o.pos = UnityObjectToClipPos(v.vertex);
o.uv = TRANSFORM_TEX(v.uv, _MainTex);
o.worldNormal = UnityObjectToWorldNormal(v.normal);
return o;
}
fixed4 frag (v2f i, fixed facing : VFACE) : SV_Target
{
fixed4 col = tex2D(_MainTex, i.uv);
// rescale alpha by mip level (if not using preserved coverage mip maps)
col.a *= 1 + max(0, CalcMipLevel(i.uv * _MainTex_TexelSize.zw)) * _MipScale;
// rescale alpha by partial derivative
col.a = (col.a - _Cutoff) / max(fwidth(col.a), 0.0001) + 0.5;
half3 worldNormal = normalize(i.worldNormal * facing);
fixed ndotl = saturate(dot(worldNormal, normalize(_WorldSpaceLightPos0.xyz)));
fixed3 lighting = ndotl * _LightColor0;
lighting += ShadeSH9(half4(worldNormal, 1.0));
col.rgb *= lighting;
return col;
}
ENDCG
}
}
}
Here is a demo of the same trick from emil persson
http://www.humus.name/index.php?page=3D&ID=61
http://www.humus.name/3D/AlphaToCoverage.zip
Further, for improving mipmapping of alpha testing/alpha to coverage is to use the alpha distribution method
http://www.cemyuksel.com/research/alphadistribution/
https://github.com/cemyuksel/cyCodeBase/blob/master/cyAlphaDistribution.h