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Emulator Issues #11626

Feature Request - MSAA for Alpha Testing via Alpha to Coverage

Added by Paleos about 2 years ago.

Status:
New
Priority:
Normal
Assignee:
-
% Done:

0%

Operating system:
N/A
Issue type:
Bug
Milestone:
Regression:
No
Relates to usability:
No
Relates to performance:
No
Easy:
No
Relates to maintainability:
No
Regression start:
Fixed in:

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

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