Casting Shadows with a transparent surface shader

[Studio-Raef]

I’m racking my brain over something stupid probably.

I’m trying to make a simple shader that allows me to load in a cloud texture and adjust the black/gray/white values so it becomes more or less transparent

And then change some values to make the clouds bigger or smaller

This works nicely and also with transparency like I want it to. But what I don’t seem to find is how I get this alpha value to work with shadows. The shadows that get cast are of the entire quad instead of what’s visible

But it I load in an image that does have transparency in the source, it does work. (the shader only affects the alpha and albedo, the projected shadow is from the alpha of the image)

Does anyone know how I could let the shadows take my calculated Alpha into account?

Here’s the shader:

Shader "Custom/CloudSurface"
{
    Properties
    {
        _Color ("Color", Color) = (1,1,1,1)
        _MainTex ("Albedo (RGB)", 2D) = "white" {}
        _LowEnd("Low End",Float) = 0.1
        _HighEnd("High End",Float) = 0.9
    }
    SubShader
    {

        Tags { "RenderType"="Transparent" "Queue" = "Transparent" }
        LOD 200
        Blend SrcAlpha OneMinusSrcAlpha

        CGPROGRAM
        // Physically based Standard lighting model, and enable shadows on all light types
        #pragma surface surf Standard fullforwardshadows alpha:fade


        // Use shader model 3.0 target, to get nicer looking lighting
        #pragma target 3.0

        sampler2D _MainTex;

        struct Input
        {
            float2 uv_MainTex;
        };

        fixed4 _Color;
        half _LowEnd;
        half _HighEnd;

        UNITY_INSTANCING_BUFFER_START(Props)
            // put more per-instance properties here
        UNITY_INSTANCING_BUFFER_END(Props)

        void surf (Input IN, inout SurfaceOutputStandard o)
        {
            // Albedo comes from a texture tinted by color
            fixed4 c = tex2D (_MainTex, IN.uv_MainTex) ;
            half cloud = clamp((c.r - _LowEnd) / (_HighEnd - _LowEnd), 0, 1);
            o.Albedo =cloud* _Color;

            o.Alpha = cloud * _Color.a;
        }
        ENDCG
       
    }
    FallBack "Standard"
}

[bgolus]

addshadow

Unity - Manual: Writing Surface Shaders

Surface Shaders by default do not generate a shadow caster pass, so your shader is just using the one from the fallback (in this case the Standard shader’s shadow caster). By adding addshadow to your #pragma surf line it’ll generate a shadow caster pass that takes into account the your surf function’s code.

However, I believe the shadow it produces will have a hard cutoff edge rather than a dithered fade like what you’re seeing, or might not work at all for alpha:fade, I forget which. The solution to that is to write a fully custom shadow caster pass instead of using addshadow.

Rendering 12

[JahnStar]

Maybe it will help someone else. Try this:
Fallback “Legacy Shaders/Transparent/Cutout/VertexLit”