A shader for Unity 3D that uses vertex colors to determine the clipping of pixels. An additional rim glow is added around the cutoff area.

EmissiveRimCutout.shader

Shader "Custom/Rim Cutout" {
	Properties {
		_Color ("Color", Color) = (1,1,1,1)
		_MainTex ("Albedo (RGB)", 2D) = "white" {}
		_Glossiness ("Smoothness", Range(0,1)) = 0.5
		_Metallic ("Metallic", Range(0,1)) = 0.0
		_RimGlowRadius("Rim Glow Radius", Range(0,1)) = 0.1
	}
	SubShader {
		Tags { "RenderType"="Opaque" }
		LOD 200
		
		CGPROGRAM
		// Physically based Standard lighting model, and enable shadows on all light types
		#pragma surface surf Standard fullforwardshadows

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

		sampler2D _MainTex;

		struct Input {
			float2 uv_MainTex;
			float4 color : COLOR;
		};

		half _Glossiness;
		half _Metallic;
		fixed4 _Color;
		float _RimGlowRadius;

		// Add instancing support for this shader. You need to check 'Enable Instancing' on materials that use the shader.
		// See https://docs.unity3d.com/Manual/GPUInstancing.html for more information about instancing.
		// #pragma instancing_options assumeuniformscaling
		UNITY_INSTANCING_CBUFFER_START(Props)
			// put more per-instance properties here
		UNITY_INSTANCING_CBUFFER_END

		void surf (Input IN, inout SurfaceOutputStandard o) {
			// Albedo comes from a texture tinted by color
			fixed4 color = tex2D(_MainTex, IN.uv_MainTex);
			fixed clipValue = IN.color.a - color.a;
			clip(clipValue);
			float emissionAmount = max(0, (_RimGlowRadius - clipValue) / _RimGlowRadius);
			o.Albedo = (clipValue * color.rgb) + (emissionAmount * IN.color.rgb);
			o.Emission = (emissionAmount * IN.color.rgb);
			// Metallic and smoothness come from slider variables
			o.Metallic = _Metallic;
			o.Smoothness = _Glossiness;
			o.Alpha = 1;
		}
		ENDCG
	}
	FallBack "Diffuse"
}