unity shader入门（三）逐像素光照，Blinn-Phong模型

与上篇逐顶点光照很像，只是改为在片元着色器中计算光照，下为逐像素光照shader

Shader "study/Chapter6/PixelShader"{
	Properties{
		_Diffuse ("Diffuse", Color) = (1, 1, 1, 1)
		}
	SubShader{
		Pass{
			Tags{"LightMode"="ForwardBase"}

			CGPROGRAM

			#pragma vertex vert
			#pragma fragment frag

			#include "Lighting.cginc"

			fixed4 _Diffuse;
			struct a2v {
				float4 vertex : POSITION;
				float3 normal : NORMAL;
			};
			
			struct v2f {
				float4 pos : SV_POSITION;
				float3 worldNormal : TEXCOORD0;
			};

			v2f vert(a2v v) {
				v2f o;
				// Transform the vertex from object space to projection space
				o.pos = UnityObjectToClipPos(v.vertex);

				// Transform the normal from object space to world space
				o.worldNormal = mul(v.normal, (float3x3)unity_WorldToObject);

				return o;
			}

			fixed4 frag(v2f i) : SV_Target {
				// Get ambient term
				fixed3 ambient = UNITY_LIGHTMODEL_AMBIENT.xyz;
				
				// Get the normal in world space
				fixed3 worldNormal = normalize(i.worldNormal);
				// Get the light direction in world space
				fixed3 worldLightDir = normalize(_WorldSpaceLightPos0.xyz);
				
				// Compute diffuse term
				fixed3 diffuse = _LightColor0.rgb * _Diffuse.rgb * saturate(dot(worldNormal, worldLightDir));
				
				fixed3 color = ambient + diffuse;
				
				return fixed4(color, 1.0);
			}
			ENDCG
		}
	}
	FallBack "Diffuse"
}

下为半兰伯特光照模型

广义的半兰伯特光照模型公式如下：

漫反射（C_diffuse）=((C_light) * (M_diffuse))(α(n*I)+β)

半兰伯特模型没有使用max防止表面法线和光照方向的点成为负值，而是进行了α倍的缩放和一个β倍的偏移，大多情况下α和β均为0.5

Shader "study/Chapter6/Half Lambert" {
	Properties {
		_Diffuse ("Diffuse", Color) = (1, 1, 1, 1)
	}
	SubShader {
		Pass { 
			Tags { "LightMode"="ForwardBase" }
		
			CGPROGRAM
			
			#pragma vertex vert
			#pragma fragment frag
			
			#include "Lighting.cginc"
			
			fixed4 _Diffuse;
			
			struct a2v {
				float4 vertex : POSITION;
				float3 normal : NORMAL;
			};
			
			struct v2f {
				float4 pos : SV_POSITION;
				float3 worldNormal : TEXCOORD0;
			};
			
			v2f vert(a2v v) {
				v2f o;
				// Transform the vertex from object space to projection space
				o.pos = UnityObjectToClipPos(v.vertex);
				
				// Transform the normal from object space to world space
				o.worldNormal = mul(v.normal, (float3x3)unity_WorldToObject);
				
				return o;
			}
			
			fixed4 frag(v2f i) : SV_Target {
				// Get ambient term
				fixed3 ambient = UNITY_LIGHTMODEL_AMBIENT.xyz;
				
				// Get the normal in world space
				fixed3 worldNormal = normalize(i.worldNormal);
				// Get the light direction in world space
				fixed3 worldLightDir = normalize(_WorldSpaceLightPos0.xyz);
				
				// Compute diffuse term
				fixed halfLambert = dot(worldNormal, worldLightDir) * 0.5 + 0.5;
				fixed3 diffuse = _LightColor0.rgb * _Diffuse.rgb * halfLambert;
				
				fixed3 color = ambient + diffuse;
				
				return fixed4(color, 1.0);
			}
			
			ENDCG
		}
	} 
	FallBack "Diffuse"
}