【渲染】逐顶点、逐片元着色

介绍

解释shading是根据光照条件重建物体各表面明暗不一的效果的过程
有三种方式Flat shading、Gouraud shading、Phong shading，就是逐三角面、逐顶点、逐片元
逐三角面用的少，这里只着重介绍Gouraud shading、Phong shading
注意per-vertex是先计算再插值，per-pixel是先插值后计算

Gouraud shading

我理解就是在顶点着色器中计算颜色，再插值给片元着色器，以unity shaderlab 的lambert举例

Shader "Unity Shaders Book/Chapter 6/Diffuse Vertex-Level" {
	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;
				fixed3 color : COLOR;
			};
			
			v2f vert(a2v v) {
				v2f o;
				// Transform the vertex from object space to projection space
				o.pos = mul(UNITY_MATRIX_MVP, v.vertex);
				
				// Get ambient term
				fixed3 ambient = UNITY_LIGHTMODEL_AMBIENT.xyz;
				
				// Transform the normal from object space to world space
				fixed3 worldNormal = normalize(mul(v.normal, (float3x3)_World2Object));
				// Get the light direction in world space
				fixed3 worldLight = normalize(_WorldSpaceLightPos0.xyz);
				// Compute diffuse term
				fixed3 diffuse = _LightColor0.rgb * _Diffuse.rgb * saturate(dot(worldNormal, worldLight));
				
				o.color = ambient + diffuse;
				
				return o;
			}
			
			fixed4 frag(v2f i) : SV_Target {
				return fixed4(i.color, 1.0);
			}
			
			ENDCG
		}
	}
	FallBack "Diffuse"
}

Phong shading

我理解就是直接在片元着色器中计算颜色

Shader "Unity Shaders Book/Chapter 6/Diffuse Pixel-Level" {
	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 = mul(UNITY_MATRIX_MVP, v.vertex);

				// Transform the normal from object space to world space
				o.worldNormal = mul(v.normal, (float3x3)_World2Object);

				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"
}