Got it to work, mostly! Ended up just pulling that entire shader I posted and changing the normal to be the derived one. Code and gif.
Shader "Custom/Default" {
Properties {
_Color ("Diffuse Material Color", Color) = (1,1,1,1)
_SpecColor ("Specular Material Color", Color) = (1,1,1,1)
_Shininess ("Shininess", Float) = 10
}
SubShader {
Pass {
Tags { "LightMode" = "ForwardBase" } // pass for
// 4 vertex lights, ambient light & first pixel light
CGPROGRAM
#pragma target 3.0
#pragma multi_compile_fwdbase
#pragma vertex vert
#pragma fragment frag
#include "UnityCG.cginc"
uniform float4 _LightColor0;
// color of light source (from "Lighting.cginc")
// User-specified properties
uniform float4 _Color;
uniform float4 _SpecColor;
uniform float _Shininess;
struct vertexInput {
float4 vertex : POSITION;
float3 normal : NORMAL;
};
struct vertexOutput {
float4 pos : SV_POSITION;
float4 posWorld : TEXCOORD0;
float3 normalDir : TEXCOORD1;
float3 vertexLighting : TEXCOORD2;
};
vertexOutput vert(vertexInput input)
{
vertexOutput output;
float4x4 modelMatrix = _Object2World;
float4x4 modelMatrixInverse = _World2Object;
// unity_Scale.w is unnecessary here
output.posWorld = mul(modelMatrix, input.vertex);
output.normalDir = normalize(
mul(float4(input.normal, 0.0), modelMatrixInverse).xyz);
output.pos = mul(UNITY_MATRIX_MVP, input.vertex);
// Diffuse reflection by four "vertex lights"
output.vertexLighting = float3(0.0, 0.0, 0.0);
#ifdef VERTEXLIGHT_ON
for (int index = 0; index < 4; index++)
{
float4 lightPosition = float4(unity_4LightPosX0[index],
unity_4LightPosY0[index],
unity_4LightPosZ0[index], 1.0);
float3 vertexToLightSource =
lightPosition.xyz - output.posWorld.xyz;
float3 lightDirection = normalize(vertexToLightSource);
float squaredDistance =
dot(vertexToLightSource, vertexToLightSource);
float attenuation = 1.0 / (1.0 +
unity_4LightAtten0[index] * squaredDistance);
float3 diffuseReflection = attenuation
* unity_LightColor[index].rgb * _Color.rgb
* max(0.0, dot(output.normalDir, lightDirection));
output.vertexLighting =
output.vertexLighting + diffuseReflection;
}
#endif
return output;
}
float4 frag(vertexOutput input) : COLOR
{
float3 posddx = ddx(input.posWorld.xyz);
float3 posddy = ddy(input.posWorld.xyz);
float3 derivedNormal = cross( normalize(posddx), normalize(posddy));
// float3 normalDirection = normalize(input.normalDir);
float3 normalDirection = normalize(derivedNormal);
float3 viewDirection = normalize(
_WorldSpaceCameraPos - input.posWorld.xyz);
float3 lightDirection;
float attenuation;
if (0.0 == _WorldSpaceLightPos0.w) // directional light?
{
attenuation = 1.0; // no attenuation
lightDirection =
normalize(_WorldSpaceLightPos0.xyz);
}
else // point or spot light
{
float3 vertexToLightSource =
_WorldSpaceLightPos0.xyz - input.posWorld.xyz;
float distance = length(vertexToLightSource);
attenuation = 1.0 / distance; // linear attenuation
lightDirection = normalize(vertexToLightSource);
}
float3 ambientLighting =
UNITY_LIGHTMODEL_AMBIENT.rgb * _Color.rgb;
float3 diffuseReflection =
attenuation * _LightColor0.rgb * _Color.rgb
* max(0.0, dot(normalDirection, lightDirection));
float3 specularReflection;
if (dot(normalDirection, lightDirection) < 0.0)
// light source on the wrong side?
{
specularReflection = float3(0.0, 0.0, 0.0);
// no specular reflection
}
else // light source on the right side
{
specularReflection = attenuation * _LightColor0.rgb
* _SpecColor.rgb * pow(max(0.0, dot(
reflect(-lightDirection, normalDirection),
viewDirection)), _Shininess);
}
return float4(input.vertexLighting + ambientLighting
+ diffuseReflection + specularReflection, 1.0);
}
ENDCG
}
}
}
I’ll need to add in the ability to handle textures and currently point lights don’t work, but I’m happy with it for now.
ShaderForge looks really great, I’m impressed at how easy it looks to build that. Good to know that both solutions work! And your gif is way higher quality than mine 
Thanks for all the help guys,
Erik
