遊戲程式設計精粹學習 - 衰減圖

燈光衰減圖可以模拟3D貼圖的效果，但也有一定的局限性。給燈光使用衰減圖可以一定程度的控制燈光形狀。

應該也是某種程度的燈光cookie。

使用衰減圖與翻頁動畫制作的燈火效果：

優點：

• 一定程度上的3D Texture
• 可以拿來做搖曳燈火等

缺點：

• 定制性比較高，真正使用可能要借助CB
• 相比3D Texture可控程度有限

原文先從泛光燈公式講起，後講到XY與Z的貼圖拆分。這裡僅大緻實作。測試shader如下：

Shader "Custom/VirtualPointLight"
{
    Properties
    {
        _MainTex("Texture", 2D) = "white" {}
        _AtteTex_XY("Atte Texture XY", 2D) = "white" {}
        _AtteTex_Z("Atte Texture Z", 2D) = "white" {}
        _VirtualLightPos("Virtual Light Position", vector) = (0, 0, 0, 0)
        _VirtualLightRange("Virtual Light Range", float) = 0.5
        _VirtualLightColor("Virtual Light Color", Color) = (0, 0, 0, 0)
        _Shininess("Shininess", range(0.1, 100)) = 1
    }

    SubShader
    {
        Tags{ "RenderType" = "Opaque" }

        Pass
        {
            CGPROGRAM
            #pragma vertex vert
            #pragma fragment frag

            #include "UnityCG.cginc"

            struct appdata
            {
                float4 vertex : POSITION;
                float2 uv : TEXCOORD0;
                float3 normal :  NORMAL;
            };

            struct v2f
            {
                float2 uv : TEXCOORD0;
                float4 vertex : SV_POSITION;
                float4 lightVolume : TEXCOORD1;
                float3 d01 : TEXCOORD2;
            };

            sampler2D _MainTex;

            sampler2D _AtteTex_XY;
            sampler2D _AtteTex_Z;

            float4 _MainTex_ST;
            float4 _VirtualLightPos;
            float4 _VirtualLightColor;
            float _Shininess;
            float _VirtualLightRange;

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

                float4 worldPosition = mul(unity_ObjectToWorld, v.vertex);
                float4 N = normalize(mul(unity_ObjectToWorld, v.normal));
                float3 d = _VirtualLightPos - worldPosition;

                o.d01 = d / _VirtualLightRange;

                float3 L = d;
                float3 V = normalize(_WorldSpaceCameraPos.xyz - worldPosition.xyz).xyz;
                float3 H = normalize(L + V);

                float4 diffuse = max(dot(N, L), 0);
                float specular = pow(max(0, dot(H, N)), _Shininess);

                o.lightVolume = diffuse + specular;
                o.lightVolume = o.lightVolume;

                return o;
            }

            fixed4 frag(v2f i) : SV_Target
            {
                fixed4 col = tex2D(_MainTex, i.uv);
                fixed d01_xy = tex2D(_AtteTex_XY, i.d01.xy + 0.5).r;
                fixed d01_z = tex2D(_AtteTex_Z, half2(i.d01.z + 0.5, 0.5)).r;

                fixed atte = 1 - (d01_xy + d01_z);
                return col * _VirtualLightColor * (i.lightVolume * atte);
            }
            ENDCG
        }
    }
}      

測試C#腳本：

public class VirtualLightBind : MonoBehaviour
{
    void Update()
    {
        material.SetVector("_VirtualLightPos", transform.position);
    }
}