Receive and cast shadows (custom GEOMETRY Grass Sh

问题:

I was following a tutorial made by Sam Wronski aka. World of Zero (Tutorial by World of Zero) where he codes a geometry shader for a point cloud grass generator. Great tutorial but I am wondering (and didn't find a proper solution after days of research) how I could implement shadows to the shader (casting and receiving shadows). I am trying to dig deeper into shaders, but this is a level to high for me yet.

My question is : how can I implement shadow casting and receiving for this grass shader? The code that exists and works fine so far is the following:

Shader "Custom/GrassGeometryShader" {

    // https://www.youtube.com/watch?v=HY6qFbmbij8 und http://www.battlemaze.com/?p=153

    Properties {
    // --> HDR allows High Dynamic Colors
        [HDR]_BackgroundColor ("Background Color", Color) = (1,0,0,1) // default to red
        [HDR]_ForegroundColor ("Foreground Color", Color) = (0,1,0,1) // default to green 
        _MainTex ("Albedo (RGB)", 2D) = "white" {}
        _Glossiness ("Smoothness", Range(0,1)) = 0.5
        _Metallic ("Metallic", Range(0,1)) = 0.0
        _Cutoff("Alpha Cuttoff", Range (0,1)) = 0.15 // Wieviel abgeschnitten sien soll
        _GrassHeight("GrasHeight", Float) = 0.25
        _GrassWidt("GrasWidth", Float) = 0.25
        _WindSpeed ("WindSpeed", Float) = 100
        _WindStrength("WindStrength", Float) = 0.05
    }
    SubShader {
        Tags { "RenderType"="Opaque" }
        LOD 200

        Pass
        {

        Cull OFF 
        CGPROGRAM
        #include "UnityCG.cginc" // like: "using" in C# 
        // Vertex-Shader with vert-function
        #pragma vertex vert
        // Fragment-Shader with frag-function
        #pragma fragment frag
        // Geometry-Shader with geom-function 
        #pragma geometry geom

        // Use shader model 3.0 target, to get nicer looking lighting
        #pragma target 4.0 // needs to be 4.0 !

        sampler2D _MainTex;

        // vertex to graphics (v2g)
        struct v2g 
        {
            float4  pos : SV_POSITION;
            float3  norm : NORMAL;
            float2  uv : TEXCOORD0;
            float3 color : TEXCOORD1;
        };

        //graphics to fragments (g2f)
        struct g2f 
        {
            float4  pos : SV_POSITION;
            float3  norm : NORMAL;
            float2  uv : TEXCOORD0;            
            float3 diffuseColor : TEXCOORD1;
            //float3 specularColor : TEXCOORD2;
        };

        half _Glossiness;
        half _Metallic;
        fixed4 _BackgroundColor;
        fixed4 _ForegroundColor;
        half _GrassHeight;
        half _GrassWidth;
        half _Cutoff;
        half _WindStrength;
        half _WindSpeed;

        // Vertex-Shader from Battlemaze.com
        v2g vert(appdata_full v)
        {
            float3 v0 = mul(unity_ObjectToWorld, v.vertex).xyz;

            v2g OUT;
            OUT.pos = v.vertex;
            OUT.norm = v.normal;
            OUT.uv = v.texcoord;
            OUT.color = tex2Dlod(_MainTex, v.texcoord).rgb;
            return OUT;         
        }

        void buldQuad(inout TriangleStream<g2f> triStream, float3 points[4], float3 color) {
            g2f OUT;
            float3 faceNormal = cross(points[1]-points[0], points[2]-points[0]);
            for(int i; i < 4; ++i) {
            OUT.pos = UnityObjectToClipPos(points[i]);
            OUT.norm = faceNormal;
            OUT.diffuseColor = color;
            OUT.uv = float2(i%2, (int)i/2);
            triStream.Append(OUT);
            }
            triStream.RestartStrip();
        }

        // geom-Funktion
        [maxvertexcount(24)]
        void geom(point v2g IN[1], inout TriangleStream<g2f> triStream)
        {
            float3 lightPosition = _WorldSpaceLightPos0;

            float3 perpendicularAngle = float3(0,0,1);
            float3 faceNormal = cross(perpendicularAngle, IN[0].norm); // normal of gras

            float3 v0 = IN[0].pos.xyz; // Tip of the gras
            float3 v1 = IN[0].pos.xyz + IN[0].norm * _GrassHeight; // base of the gras
            float3 v2 = IN[0].pos.xyz + IN[0].norm * _GrassHeight / 2; // middle part (?)

            float3 wind = float3(sin(_Time.x * _WindSpeed + v0.x) + sin(_Time.x * _WindSpeed + v0.z * 2), 0, cos(_Time.x * _WindSpeed + v0.x * 2) + cos(_Time.x * _WindSpeed + v0.z)); // Anzahl oder Stärke der Manipulation an den Eckpunkten 
            // (_Time.x + v0.x + v0.z looks "random", because it's using time + coordinates)

            v1 += wind * _WindStrength;
            v2 += (wind * _WindStrength/2)/2;

            float3 color = (IN[0].color); // color of the gras

            float sin30 = 0.5;
            float sin60 = 0.866f;
            float cos30 = sin60;
            float cos60 = sin30;

            g2f OUT;

            // Quad 1 - the following code could fit in one function (BUT!) it did not work on MacOSX, that's why it's still calculated the long way

        OUT.pos = UnityObjectToClipPos(v0 + perpendicularAngle * 0.5 * _GrassHeight);
        OUT.norm = faceNormal;
        OUT.diffuseColor = color;
        OUT.uv = float2(1, 0);
        triStream.Append(OUT);


        OUT.pos = UnityObjectToClipPos(v1 + perpendicularAngle * 0.5 * _GrassHeight);
        OUT.norm = faceNormal;
        OUT.diffuseColor = color;
        OUT.uv = float2(1, 1);
        triStream.Append(OUT);

        OUT.pos = UnityObjectToClipPos(v0);
        OUT.norm = faceNormal;
        OUT.diffuseColor = color;
        OUT.uv = float2(0.5, 0);
        triStream.Append(OUT);

        OUT.pos = UnityObjectToClipPos(v1);
        OUT.norm = faceNormal;
        OUT.diffuseColor = color;
        OUT.uv = float2(0.5, 1);
        triStream.Append(OUT);

        OUT.pos = UnityObjectToClipPos(v1 - perpendicularAngle * 0.5 * _GrassHeight);
        OUT.norm = faceNormal;
        OUT.diffuseColor = color;
        OUT.uv = float2(0, 1);
        triStream.Append(OUT);

        OUT.pos = UnityObjectToClipPos(v0 - perpendicularAngle * 0.5 * _GrassHeight);
        OUT.norm = faceNormal;
        OUT.diffuseColor = color;
        OUT.uv = float2(0, 0);
        triStream.Append(OUT);

        OUT.pos = UnityObjectToClipPos(v0);
        OUT.norm = faceNormal;
        OUT.diffuseColor = color;
        OUT.uv = float2(0.5, 0);
        triStream.Append(OUT);

        OUT.pos = UnityObjectToClipPos(v1);
        OUT.norm = faceNormal;
        OUT.diffuseColor = color;
        OUT.uv = float2(0.5, 1);
        triStream.Append(OUT);

        // Quad 2

        OUT.pos = UnityObjectToClipPos(v0 + float3(sin60, 0, -cos60) * 0.5 * _GrassHeight);
        OUT.norm = faceNormal;
        OUT.diffuseColor = color;
        OUT.uv = float2(1, 0);
        triStream.Append(OUT);

        OUT.pos = UnityObjectToClipPos(v1 + float3(sin60, 0, -cos60)* 0.5 * _GrassHeight);
        OUT.norm = faceNormal;
        OUT.diffuseColor = color;
        OUT.uv = float2(1, 1);
        triStream.Append(OUT);

        OUT.pos = UnityObjectToClipPos(v0);
        OUT.norm = faceNormal;
        OUT.diffuseColor = color;
        OUT.uv = float2(0.5, 0);
        triStream.Append(OUT);

        OUT.pos = UnityObjectToClipPos(v1);
        OUT.norm = faceNormal;
        OUT.diffuseColor = color;
        OUT.uv = float2(0.5, 1);
        triStream.Append(OUT);

        OUT.pos = UnityObjectToClipPos(v0 - float3(sin60, 0, -cos60) * 0.5 * _GrassHeight);
        OUT.norm = faceNormal;
        OUT.diffuseColor = color;
        OUT.uv = float2(0, 0);
        triStream.Append(OUT);

        OUT.pos = UnityObjectToClipPos(v1 - float3(sin60, 0, -cos60) * 0.5 * _GrassHeight);
        OUT.norm = faceNormal;
        OUT.diffuseColor = color;
        OUT.uv = float2(0, 1);
        triStream.Append(OUT);

        OUT.pos = UnityObjectToClipPos(v0);
        OUT.norm = faceNormal;
        OUT.diffuseColor = color;
        OUT.uv = float2(0.5, 0);
        triStream.Append(OUT);

        OUT.pos = UnityObjectToClipPos(v1);
        OUT.norm = faceNormal;
        OUT.diffuseColor = color;
        OUT.uv = float2(0.5, 1);
        triStream.Append(OUT);

        // Quad 3 - Positive

        OUT.pos = UnityObjectToClipPos(v0 + float3(sin60, 0, cos60) * 0.5 * _GrassHeight);
        OUT.norm = faceNormal;
        OUT.diffuseColor = color;
        OUT.uv = float2(1, 0);
        triStream.Append(OUT);

        OUT.pos = UnityObjectToClipPos(v1 + float3(sin60, 0, cos60)* 0.5 * _GrassHeight);
        OUT.norm = faceNormal;
        OUT.diffuseColor = color;
        OUT.uv = float2(1, 1);
        triStream.Append(OUT);

        OUT.pos = UnityObjectToClipPos(v0);
        OUT.norm = faceNormal;
        OUT.diffuseColor = color;
        OUT.uv = float2(0.5, 0);
        triStream.Append(OUT);

        OUT.pos = UnityObjectToClipPos(v1);
        OUT.norm = faceNormal;
        OUT.diffuseColor = color;
        OUT.uv = float2(0.5, 1);
        triStream.Append(OUT);

        OUT.pos = UnityObjectToClipPos(v0 - float3(sin60, 0, cos60) * 0.5 * _GrassHeight);
        OUT.norm = faceNormal;
        OUT.diffuseColor = color;
        OUT.uv = float2(0, 0);
        triStream.Append(OUT);

        OUT.pos = UnityObjectToClipPos(v1 - float3(sin60, 0, cos60) * 0.5 * _GrassHeight);
        OUT.norm = faceNormal;
        OUT.diffuseColor = color;
        OUT.uv = float2(0, 1);
        triStream.Append(OUT);

        OUT.pos = UnityObjectToClipPos(v0);
        OUT.norm = faceNormal;
        OUT.diffuseColor = color;
        OUT.uv = float2(0.5, 0);
        triStream.Append(OUT);

        OUT.pos = UnityObjectToClipPos(v1);
        OUT.norm = faceNormal;
        OUT.diffuseColor = color;
        OUT.uv = float2(0.5, 1);
        triStream.Append(OUT);

        }

        // Fragment-Shader by Battlemaze.com --> gets input v2g and renders it on screen
        half4 frag(g2f IN) : COLOR
        {
            fixed4 c = tex2D(_MainTex, IN.uv);
            clip(c.a - _Cutoff);
            return c;
            //return float4 (IN.diffuseColor.rgb, 1.0);
        }

        ENDCG
        }
    }
}

As I mentioned I work with a machine running MacOS which does unfortunately not work with compute shaders.

I would appreciate any help on this.

回答1:

To add support for shadow receiving

To the top of the CGPROGRAM block, add this:

#include "AutoLight.cginc"

It is also possible that you might need to add this:

#pragma multi_compile_fwdbase

Inside your v2g struct, add the following line:

SHADOW_COORDS(3) // (3) means we are using TEXCOORD3

Inside your geometry shader, for each new vertex, add this line after you've assigned OUT.pos:

TRANSFER_SHADOW(OUT)

And finally, in your fragment function, add this:

half shadow = SHADOW_ATTENUATION(IN)

Now, the "shadow" variable contains your shadow mask. In a lit shader, you'd multiply this with the light color, but in your case you can just multiply it with the output albedo color.

---

To add support for shadow casting

Add the following pass to your shader:

Pass {
    Name "ShadowCaster"
    Tags { "LightMode" = "ShadowCaster" }

    ZWrite On ZTest LEqual

    CGPROGRAM
    #pragma target 2.0

    #pragma multi_compile_shadowcaster

    #pragma vertex vertShadowCaster
    #pragma fragment fragShadowCaster

    #include "UnityStandardShadow.cginc"

    ENDCG
}