How would I mask this geometry shader with a texture?

Unity Engine
1

This shader makes little triangle (billboards) on each vertex of a mesh.

3184804--243028--upload_2017-8-15_15-8-20.png
3184804--243028--upload_2017-8-15_15-8-20.png1003×666 84.4 KB

I want to have an additional texture that masks where the points are. For example, I could put this shader on a sphere and supply a checkerboard texture. Then there would be a checkerboard pattern of showing/hiding the billboards. Or I could use a height map of the Earth and points would only be rendered where the texture is bright enough.

I tried figuring it out, but I’ve never used a geometry shader before (and didn’t write this one) I couldn’t figure out how to same a texture from the uv coordinates of the original mesh. Instead it would sample the new texture from the uvs of the new mesh. It seems like I’ve got the right idea but I would love a hint to send me in the right direction.

Shader "Unlit/PointCloud"
{
    Properties
    {
        _MainTex ("Texture (RGB)", 2D) = "white" {}
        _Size ("Size", Float) = 0.1
    }
    SubShader
    {
        Tags { "Queue"="AlphaTest" "RenderType"="Transparent" "IgnoreProjector"="True" }
        Blend One OneMinusSrcAlpha
        AlphaToMask On
        Cull Off

        Pass
        {
            CGPROGRAM
            #pragma vertex vert
            #pragma geometry geom
            #pragma fragment frag
        
            #include "UnityCG.cginc"

            sampler2D _MainTex;
            float _Size;

            struct GS_INPUT
            {
                float4 vertex : POSITION;
                float3 normal    : NORMAL;
                float4 color    : COLOR;
                float2 texcoord : TEXCOORD0;
                float2 texcoord1 : TEXCOORD1;
            };

            struct FS_INPUT {
                float4 vertex : SV_POSITION;
                float3 normal : NORMAL;
                float4 color : COLOR;
                float2 texcoord : TEXCOORD0;
            };

            GS_INPUT vert (appdata_full v)
            {
                GS_INPUT o = (GS_INPUT)0;
                o.vertex = v.vertex;
                o.normal = v.normal;
                o.color = v.color;
                return o;
            }


            [maxvertexcount(3)]
            void geom (point GS_INPUT tri[1], inout TriangleStream<FS_INPUT> triStream)
            {
                FS_INPUT pIn = (FS_INPUT)0;
                pIn.normal = mul(unity_ObjectToWorld, tri[0].normal);
                pIn.color = tri[0].color;

                float4 vertex = mul(unity_ObjectToWorld, tri[0].vertex);
                float3 tangent = normalize(cross(float3(0,1,0), pIn.normal));
                float3 up = normalize(cross(tangent, pIn.normal));

                pIn.vertex = mul(UNITY_MATRIX_VP, vertex + float4(tangent * -_Size / 1.5, 0));
                pIn.texcoord = float2(-0.5,0);
                triStream.Append(pIn);

                pIn.vertex = mul(UNITY_MATRIX_VP, vertex + float4(up * _Size, 0));
                pIn.texcoord = float2(0.5,1.5);
                triStream.Append(pIn);

                pIn.vertex = mul(UNITY_MATRIX_VP, vertex + float4(tangent * _Size / 1.5, 0));
                pIn.texcoord = float2(1.5,0);
                triStream.Append(pIn);
            }

            float4 frag (FS_INPUT i) : COLOR
            {
                float4 color = i.color;
                color.a = step(0.5, tex2D(_MainTex, i.texcoord).a);
                return color;
            }
            ENDCG
        }
    }
}
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2

Any solution for this??? i’m looking to do the same thing!

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