Cg shadow of sphere

参考自：https://en.wikibooks.org/wiki/GLSL_Programming/Unity/Soft_Shadows_of_Spheres

using UnityEngine;
using System.Collections;
[ExecuteInEditMode]
public class TestShadowOfSphere : MonoBehaviour {
    public GameObject occluder;
    // Use this for initialization
    void Start () {
	
	}
	
	// Update is called once per frame
	void Update () {
        if (null != occluder)
        {
            GetComponent<Renderer>().sharedMaterial.SetVector("_SpherePosition",
               occluder.transform.position);
            GetComponent<Renderer>().sharedMaterial.SetFloat("_SphereRadius",
               occluder.transform.localScale.x / 2.0f);
        }
    }
}

　　

Shader "Cg shadow of sphere" {
	Properties{
		_Color("Diffuse Material Color", Color) = (1,1,1,1)
		_SpecColor("Specular Material Color", Color) = (1,1,1,1)
		_Shininess("Shininess", Float) = 10
		_SpherePosition("Sphere Position", Vector) = (0,0,0,1)
		_SphereRadius("Sphere Radius", Float) = 1
		_LightSourceRadius("Light Source Radius", Float) = 0.005
	}
	SubShader{
		Pass{
			Tags{ "LightMode" = "ForwardBase" }
		// pass for ambient light and first light source

		CGPROGRAM
		#pragma vertex vert  
		#pragma fragment frag 
		#pragma target 3.0
		#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;
		uniform float4 _SpherePosition;
		// center of shadow-casting sphere in world coordinates
		uniform float _SphereRadius;
		// radius of shadow-casting sphere
		uniform float _LightSourceRadius;
		// in radians for directional light sources

		struct vertexInput {
			float4 vertex : POSITION;
			float3 normal : NORMAL;
		};
		struct vertexOutput {
			float4 pos : SV_POSITION;
			float4 posWorld : TEXCOORD0;
			float3 normalDir : TEXCOORD1;
		};

		vertexOutput vert(vertexInput input){
			vertexOutput output;

			float4x4 modelMatrix = _Object2World;
			float4x4 modelMatrixInverse = _World2Object;

			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);
			return output;
		}

		float4 frag(vertexOutput input) : COLOR{
			float3 normalDirection = normalize(input.normalDir);

			float3 viewDirection = normalize(
				_WorldSpaceCameraPos - input.posWorld.xyz);
			float3 lightDirection;
			float lightDistance;
			float attenuation;

			if (0.0 == _WorldSpaceLightPos0.w) // directional light?
			{
				attenuation = 1.0; // no attenuation
				lightDirection =
					normalize(_WorldSpaceLightPos0.xyz);
				lightDistance = 1.0;
			}
			else // point or spot light
			{
				lightDirection =
					_WorldSpaceLightPos0.xyz - input.posWorld.xyz;
				lightDistance = length(lightDirection);
				attenuation = 1.0 / lightDistance; // linear attenuation
				lightDirection = lightDirection / lightDistance;
			}

			// computation of level of shadowing w  
			float3 sphereDirection =
				_SpherePosition.xyz - input.posWorld.xyz;
			float sphereDistance = length(sphereDirection);
			sphereDirection = sphereDirection / sphereDistance;
			float d = lightDistance
				* (asin(min(1.0,
					length(cross(lightDirection, sphereDirection))))
					- asin(min(1.0, _SphereRadius / sphereDistance)));
			float w = smoothstep(-1.0, 1.0, -d / _LightSourceRadius);
			w = w * smoothstep(0.0, 0.2,
				dot(lightDirection, sphereDirection));
			if (0.0 != _WorldSpaceLightPos0.w) // point light source?
			{
				w = w * smoothstep(0.0, _SphereRadius,
					lightDistance - sphereDistance);
			}

			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(ambientLighting
					+ (1.0 - w) * (diffuseReflection + specularReflection),
					1.0);
			}

			ENDCG
		}

		Pass{
			Tags{ "LightMode" = "ForwardAdd" }
			// pass for additional light sources
			Blend One One // additive blending 

			CGPROGRAM
			#pragma vertex vert  
			#pragma fragment frag 

			#pragma target 3.0

			#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;
			uniform float4 _SpherePosition;
			// center of shadow-casting sphere in world coordinates
			uniform float _SphereRadius;
			// radius of shadow-casting sphere
			uniform float _LightSourceRadius;
			// in radians for directional light sources

			struct vertexInput {
				float4 vertex : POSITION;
				float3 normal : NORMAL;
			};
			struct vertexOutput {
				float4 pos : SV_POSITION;
				float4 posWorld : TEXCOORD0;
				float3 normalDir : TEXCOORD1;
			};

			vertexOutput vert(vertexInput input)
			{
				vertexOutput output;

				float4x4 modelMatrix = _Object2World;
				float4x4 modelMatrixInverse = _World2Object;

				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);
				return output;
			}

			float4 frag(vertexOutput input) : COLOR
			{
				float3 normalDirection = normalize(input.normalDir);

				float3 viewDirection = normalize(
					_WorldSpaceCameraPos - input.posWorld.xyz);
				float3 lightDirection;
				float lightDistance;
				float attenuation;

				if (0.0 == _WorldSpaceLightPos0.w) // directional light?
				{
					attenuation = 1.0; // no attenuation
					lightDirection = normalize(_WorldSpaceLightPos0.xyz);
					lightDistance = 1.0;
				}
				else // point or spot light
				{
					lightDirection =
						_WorldSpaceLightPos0.xyz - input.posWorld.xyz;
					lightDistance = length(lightDirection);
					attenuation = 1.0 / lightDistance; // linear attenuation
					lightDirection = lightDirection / lightDistance;
				}

				// computation of level of shadowing w  
				float3 sphereDirection =
					_SpherePosition.xyz - input.posWorld.xyz;
				float sphereDistance = length(sphereDirection);
				sphereDirection = sphereDirection / sphereDistance;
				float d = lightDistance
					* (asin(min(1.0,
						length(cross(lightDirection, sphereDirection))))
						- asin(min(1.0, _SphereRadius / sphereDistance)));
				float w = smoothstep(-1.0, 1.0, -d / _LightSourceRadius);
				w = w * smoothstep(0.0, 0.2,
					dot(lightDirection, sphereDirection));
				if (0.0 != _WorldSpaceLightPos0.w) // point light source?
				{
					w = w * smoothstep(0.0, _SphereRadius,
						lightDistance - sphereDistance);
				}

				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((1.0 - w) * (diffuseReflection + specularReflection), 1.0);
			}
			ENDCG
		}
	}
	Fallback "Specular"
}