February 19, 2023

Unity Shader 学习 Tessellation(曲面细分)

Unity Shader 学习 Tessellation(曲面细分)

关于Tessellation Shader

下图是渲染流程中的Shader顺序�?/p>

aHR0cDovL2ltZy5ibG9nLmNzZG4ubmV0LzIwMTcwNzEyMTgxMDAxMzE0.png

将Tessellation Shader展开后，请看下图�?/p>

aHR0cDovL2ltZy5ibG9nLmNzZG4ubmV0LzIwMTcwNzEyMTgxMDU5NzQy.png

也就是说我们要通过 Hull Shader �?Domain Shader 来控制Tessellation的实现�?/p> 

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   Shader "Unlit/Tessellation"
   {
Properties
{
	_MainTex ("Texture", 2D) = "white" {}
}
SubShader
{
	Tags { "RenderType"="Opaque" }
	LOD 100

	Pass
	{
		CGPROGRAM
		#pragma vertex tessvert
		#pragma fragment frag
		#pragma hull hs
		#pragma domain ds
		#pragma target 4.6
		
		#include "UnityCG.cginc"
		#include "Lighting.cginc"

		struct appdata
		{
			float4 vertex : POSITION;
			float4 tangent : TANGENT;
               float3 normal : NORMAL;
               float2 texcoord : TEXCOORD0;
		};

		struct v2f
		{
			float2 texcoord:TEXCOORD0;
			float4 vertex : SV_POSITION;
			float4 tangent : TANGENT;
 				float3 normal : NORMAL;
		};

		struct InternalTessInterp_appdata {
		  float4 vertex : INTERNALTESSPOS;
		  float4 tangent : TANGENT;
		  float3 normal : NORMAL;
		  float2 texcoord : TEXCOORD0;
		};

		sampler2D _MainTex;
		float4 _MainTex_ST;
           
		InternalTessInterp_appdata tessvert (appdata v) {
		  InternalTessInterp_appdata o;
		  o.vertex = v.vertex;
		  o.tangent = v.tangent;
		  o.normal = v.normal;
		  o.texcoord = v.texcoord;
		  return o;
		}


		v2f vert (appdata v)
		{
			v2f o;
			o.vertex = UnityObjectToClipPos(v.vertex);
			o.texcoord = TRANSFORM_TEX(v.texcoord, _MainTex);
			return o;
		}


		UnityTessellationFactors hsconst (InputPatch<InternalTessInterp_appdata,3> v) {
		  UnityTessellationFactors o;
		  float4 tf;
             //定义曲面细分的参�?/span>
		  tf = float4(4.0f,4.0f,4.0f,4.0f);
		  o.edge[0] = tf.x; 
		  o.edge[1] = tf.y; 
		  o.edge[2] = tf.z; 
		  o.inside = tf.w;
		  return o;
		}

		[UNITY_domain("tri")]//确定图元，quad,triangle�?/span>
		[UNITY_partitioning("fractional_odd")]]//拆分edge的规则，equal_spacing,fractional_odd,fractional_even
		[UNITY_outputtopology("triangle_cw")]
		[UNITY_patchconstantfunc("hsconst")]//一个patch一共有三个点，但是这三个点都共用这个函�?/span>
		[UNITY_outputcontrolpoints(3)]//不同的图元会对应不同的控制点
		InternalTessInterp_appdata hs (InputPatch<InternalTessInterp_appdata,3> v, uint id : SV_OutputControlPointID) {
		  return v[id];
		}

		[UNITY_domain("tri")]
		v2f ds (UnityTessellationFactors tessFactors, const OutputPatch<InternalTessInterp_appdata,3> vi, float3 bary : SV_DomainLocation) {
		  appdata v;

		  v.vertex = vi[0].vertex*bary.x + vi[1].vertex*bary.y + vi[2].vertex*bary.z;
		  v.tangent = vi[0].tangent*bary.x + vi[1].tangent*bary.y + vi[2].tangent*bary.z;
		  v.normal = vi[0].normal*bary.x + vi[1].normal*bary.y + vi[2].normal*bary.z;
		  v.texcoord = vi[0].texcoord*bary.x + vi[1].texcoord*bary.y + vi[2].texcoord*bary.z;

		  v2f o = vert (v);
		  return o;
		}

		
		fixed4 frag (v2f i) : SV_Target
		{
			return fixed4(1.0f,1.0f,1.0f,1.0f);
		}
		ENDCG
	}
}
   }


根据距离进行不同级别的细�?/p> 

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texInput vert(vertexInput0 v)
{
    vertexInput vi;
        //计算距离因子
    float dist = distance(_WorldSpaceCameraPos,mul(unity_ObjectToWorld, v.vertex))/(16*5);
    vi.vertex = v.vertex;
    vi.normal = v.normal;
    vi.tangent = v.tangent;
    float tf = (int)(lerp(5.2, 1.2, clamp(dist, 0.0, 1)));
    if(tf==5)tf=4;
    //tf = ((int)(tf*10))/10.0;
    vi.TessFactor = tf;
    return vi;
}

TessellationFactors patchConstantFunction (InputPatch<vertexInput, 3> patch)
{
    TessellationFactors tf;

    //tf.edge[0] = _TessellationUniform;
    //tf.edge[1] = _TessellationUniform;
    //tf.edge[2] = _TessellationUniform;
    //tf.inside = _TessellationUniform;

        //使用基于距离�?Tessellation
    tfTessellation.edge[0] = 0.5fTTTessellation*(patch[1].TessFactor + patch[2].TessFactor);
    tf.edge[1] = 0.5f*(patch[2].TessFactor + patch[0].TessFactor);
    tf.edge[2] = 0.5f*(patch[0].TessFactor + patch[1].TessFactor);
    tf.inside  = tf.edge[0];

    return tf;
}

关于本文

本文作�?Master Gong Sheng, 许可�?CC BY-NC 4.0.