Texture Matrix in Fixed Function

Shader "Projector/Projector Multiply"
{ 
Properties
{
    _Color ("Main Colour", Color) = (1,1,1,0)
    _ShadowTex ("Cookie", 2D) = "gray" { TexGen ObjectLinear }
}

Subshader
{
    Tags { "RenderType"="Transparent"  "Queue"="Transparent+100"}
    Pass
    {
        ZWrite Off
        Offset -1, -1

        Fog { Mode Off }

        //AlphaTest Greater .1
        AlphaTest Less 1
        ColorMask RGB
        Blend One SrcAlpha

        SetTexture [_ShadowTex]
        {
            constantColor [_Color]
            combine texture * constant, One - texture
            Matrix [_Projector]
        }
    }
}
}

We slightly modified it so that it can take a color and removed the falloff texture, but that's pretty much what you'll find in the Projectors package BlobShadow prefab shader.

Since I want way better control about the way this is all rendered, and since like every sane person I hate fixed-functions shader programming, I wanted to move it to CG code. My puny and failed attempt at simply reproducing what the fixed function shader was doing looks like this: