Silhouette-Outlined Diffuse

http://wiki.unity3d.com/index.php/Silhouette-Outlined_Diffuse

A variant of Outlined Diffuse 3 showing outlines only at the exteriors of the object. Useful for showing
which character is selected in a strategy game, for example.

Notice the left foot is far too down the ground.

The outline is merely the object in question but scaled upwards, rendered in a single color, and it always shows on top of everything (like the tree here), except the object it is outlining. You can remove the "showing on top" effect by removing all occurrences
of "ZTest Always"

Shader "Outlined/Silhouetted Diffuse" {
	Properties {
		_Color ("Main Color", Color) = (.5,.5,.5,1)
		_OutlineColor ("Outline Color", Color) = (0,0,0,1)
		_Outline ("Outline width", Range (0.0, 0.03)) = .005
		_MainTex ("Base (RGB)", 2D) = "white" { }
	}
 
CGINCLUDE
#include "UnityCG.cginc"
 
struct appdata {
	float4 vertex : POSITION;
	float3 normal : NORMAL;
};
 
struct v2f {
	float4 pos : POSITION;
	float4 color : COLOR;
};
 
uniform float _Outline;
uniform float4 _OutlineColor;
 
v2f vert(appdata v) {
	// just make a copy of incoming vertex data but scaled according to normal direction
	v2f o;
	o.pos = mul(UNITY_MATRIX_MVP, v.vertex);
 
	float3 norm   = mul ((float3x3)UNITY_MATRIX_IT_MV, v.normal);
	float2 offset = TransformViewToProjection(norm.xy);
 
	o.pos.xy += offset * o.pos.z * _Outline;
	o.color = _OutlineColor;
	return o;
}
ENDCG
 
	SubShader {
		Tags { "Queue" = "Transparent" }
 
		// note that a vertex shader is specified here but its using the one above
		Pass {
			Name "OUTLINE"
			Tags { "LightMode" = "Always" }
			Cull Off
			ZWrite Off
			ZTest Always
			ColorMask RGB // alpha not used
 
			// you can choose what kind of blending mode you want for the outline
			Blend SrcAlpha OneMinusSrcAlpha // Normal
			//Blend One One // Additive
			//Blend One OneMinusDstColor // Soft Additive
			//Blend DstColor Zero // Multiplicative
			//Blend DstColor SrcColor // 2x Multiplicative
 
CGPROGRAM
#pragma vertex vert
#pragma fragment frag
 
half4 frag(v2f i) :COLOR {
	return i.color;
}
ENDCG
		}
 
		Pass {
			Name "BASE"
			ZWrite On
			ZTest LEqual
			Blend SrcAlpha OneMinusSrcAlpha
			Material {
				Diffuse [_Color]
				Ambient [_Color]
			}
			Lighting On
			SetTexture [_MainTex] {
				ConstantColor [_Color]
				Combine texture * constant
			}
			SetTexture [_MainTex] {
				Combine previous * primary DOUBLE
			}
		}
	}
 
	SubShader {
		Tags { "Queue" = "Transparent" }
 
		Pass {
			Name "OUTLINE"
			Tags { "LightMode" = "Always" }
			Cull Front
			ZWrite Off
			ZTest Always
			ColorMask RGB
 
			// you can choose what kind of blending mode you want for the outline
			Blend SrcAlpha OneMinusSrcAlpha // Normal
			//Blend One One // Additive
			//Blend One OneMinusDstColor // Soft Additive
			//Blend DstColor Zero // Multiplicative
			//Blend DstColor SrcColor // 2x Multiplicative
 
			CGPROGRAM
			#pragma vertex vert
			#pragma exclude_renderers gles xbox360 ps3
			ENDCG
			SetTexture [_MainTex] { combine primary }
		}
 
		Pass {
			Name "BASE"
			ZWrite On
			ZTest LEqual
			Blend SrcAlpha OneMinusSrcAlpha
			Material {
				Diffuse [_Color]
				Ambient [_Color]
			}
			Lighting On
			SetTexture [_MainTex] {
				ConstantColor [_Color]
				Combine texture * constant
			}
			SetTexture [_MainTex] {
				Combine previous * primary DOUBLE
			}
		}
	}
 
	Fallback "Diffuse"
}

Bumped version:

Shader "Outlined/Silhouetted Bumped Diffuse" {
	Properties {
		_Color ("Main Color", Color) = (.5,.5,.5,1)
		_OutlineColor ("Outline Color", Color) = (0,0,0,1)
		_Outline ("Outline width", Range (0.0, 0.03)) = .005
		_MainTex ("Base (RGB)", 2D) = "white" { }
		_BumpMap ("Bumpmap", 2D) = "bump" {}
	}
 
CGINCLUDE
#include "UnityCG.cginc"
 
struct appdata {
	float4 vertex : POSITION;
	float3 normal : NORMAL;
};
 
struct v2f {
	float4 pos : POSITION;
	float4 color : COLOR;
};
 
uniform float _Outline;
uniform float4 _OutlineColor;
 
v2f vert(appdata v) {
	// just make a copy of incoming vertex data but scaled according to normal direction
	v2f o;
	o.pos = mul(UNITY_MATRIX_MVP, v.vertex);
 
	float3 norm   = mul ((float3x3)UNITY_MATRIX_IT_MV, v.normal);
	float2 offset = TransformViewToProjection(norm.xy);
 
	o.pos.xy += offset * o.pos.z * _Outline;
	o.color = _OutlineColor;
	return o;
}
ENDCG
 
	SubShader {
		Tags { "Queue" = "Transparent" }
 
		// note that a vertex shader is specified here but its using the one above
		Pass {
			Name "OUTLINE"
			Tags { "LightMode" = "Always" }
			Cull Off
			ZWrite Off
			ZTest Always
 
			// you can choose what kind of blending mode you want for the outline
			Blend SrcAlpha OneMinusSrcAlpha // Normal
			//Blend One One // Additive
			//Blend One OneMinusDstColor // Soft Additive
			//Blend DstColor Zero // Multiplicative
			//Blend DstColor SrcColor // 2x Multiplicative
 
CGPROGRAM
#pragma vertex vert
#pragma fragment frag
 
half4 frag(v2f i) : COLOR {
	return i.color;
}
ENDCG
		}
 
 
CGPROGRAM
#pragma surface surf Lambert
struct Input {
	float2 uv_MainTex;
	float2 uv_BumpMap;
};
sampler2D _MainTex;
sampler2D _BumpMap;
uniform float3 _Color;
void surf(Input IN, inout SurfaceOutput o) {
	o.Albedo = tex2D(_MainTex, IN.uv_MainTex).rgb * _Color;
	o.Normal = UnpackNormal(tex2D(_BumpMap, IN.uv_BumpMap));
}
ENDCG
 
	}
 
	SubShader {
		Tags { "Queue" = "Transparent" }
 
		Pass {
			Name "OUTLINE"
			Tags { "LightMode" = "Always" }
			Cull Front
			ZWrite Off
			ZTest Always
			Offset 15,15
 
			// you can choose what kind of blending mode you want for the outline
			Blend SrcAlpha OneMinusSrcAlpha // Normal
			//Blend One One // Additive
			//Blend One OneMinusDstColor // Soft Additive
			//Blend DstColor Zero // Multiplicative
			//Blend DstColor SrcColor // 2x Multiplicative
 
			CGPROGRAM
			#pragma vertex vert
			#pragma exclude_renderers gles xbox360 ps3
			ENDCG
			SetTexture [_MainTex] { combine primary }
		}
 
CGPROGRAM
#pragma surface surf Lambert
struct Input {
	float2 uv_MainTex;
	float2 uv_BumpMap;
};
sampler2D _MainTex;
sampler2D _BumpMap;
uniform float3 _Color;
void surf(Input IN, inout SurfaceOutput o) {
	o.Albedo = tex2D(_MainTex, IN.uv_MainTex).rgb * _Color;
	o.Normal = UnpackNormal(tex2D(_BumpMap, IN.uv_BumpMap));
}
ENDCG
 
	}
 
	Fallback "Outlined/Silhouetted Diffuse"
}

Outline Only Variant

The thing that does the trick here is "Blend Zero One" which is to completely forego rendering our object and use only the destination color (i.e. whatever is behind the object). In effect, the object itself is invisible, but we still let the outline render
itself. So that's what we're left with: only the outline.

Shader "Outlined/Silhouette Only" {
	Properties {
		_OutlineColor ("Outline Color", Color) = (0,0,0,1)
		_Outline ("Outline width", Range (0.0, 0.03)) = .005
	}
 
CGINCLUDE
#include "UnityCG.cginc"
 
struct appdata {
	float4 vertex : POSITION;
	float3 normal : NORMAL;
};
 
struct v2f {
	float4 pos : POSITION;
	float4 color : COLOR;
};
 
uniform float _Outline;
uniform float4 _OutlineColor;
 
v2f vert(appdata v) {
	// just make a copy of incoming vertex data but scaled according to normal direction
	v2f o;
	o.pos = mul(UNITY_MATRIX_MVP, v.vertex);
 
	float3 norm   = mul ((float3x3)UNITY_MATRIX_IT_MV, v.normal);
	float2 offset = TransformViewToProjection(norm.xy);
 
	o.pos.xy += offset * o.pos.z * _Outline;
	o.color = _OutlineColor;
	return o;
}
ENDCG
 
	SubShader {
		Tags { "Queue" = "Transparent" }
 
		Pass {
			Name "BASE"
			Cull Back
			Blend Zero One
 
			// uncomment this to hide inner details:
			//Offset -8, -8
 
			SetTexture [_OutlineColor] {
				ConstantColor (0,0,0,0)
				Combine constant
			}
		}
 
		// note that a vertex shader is specified here but its using the one above
		Pass {
			Name "OUTLINE"
			Tags { "LightMode" = "Always" }
			Cull Front
 
			// you can choose what kind of blending mode you want for the outline
			//Blend SrcAlpha OneMinusSrcAlpha // Normal
			//Blend One One // Additive
			Blend One OneMinusDstColor // Soft Additive
			//Blend DstColor Zero // Multiplicative
			//Blend DstColor SrcColor // 2x Multiplicative
 
CGPROGRAM
#pragma vertex vert
#pragma fragment frag
 
half4 frag(v2f i) :COLOR {
	return i.color;
}
ENDCG
		}
 
 
	}
 
	Fallback "Diffuse"
}