1.从Unlit-Color开始入手

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Shader 源码-Unlit-Color

需要有一定的shader基础，深刻理解unity 内置shader的实现原里。

先贴代码，逐步分析

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// Unity built-in shader source. Copyright (c) 2016 Unity Technologies. MIT license (see license.txt)

// Unlit shader. Simplest possible colored shader.
// - no lighting
// - no lightmap support
// - no texture

Shader "Unlit/Color"
{
    Properties
    {
        _Color ("Main Color", Color) = (1, 1, 1, 1)
    }

    SubShader
    {
        Tags { "RenderType" = "Opaque" }
        LOD 100

        Pass
        {
            CGPROGRAM
            
            #pragma vertex vert
            #pragma fragment frag
            #pragma target 2.0
            #pragma multi_compile_fog

            #include "UnityCG.cginc"

            struct appdata_t
            {
                float4 vertex: POSITION;
                UNITY_VERTEX_INPUT_INSTANCE_ID
            };

            struct v2f
            {
                float4 vertex: SV_POSITION;
                UNITY_FOG_COORDS(0)
                UNITY_VERTEX_OUTPUT_STEREO
            };

            fixed4 _Color;

            v2f vert(appdata_t v)
            {
                v2f o;
                UNITY_SETUP_INSTANCE_ID(v);
                UNITY_INITIALIZE_VERTEX_OUTPUT_STEREO(o);
                o.vertex = UnityObjectToClipPos(v.vertex);
                UNITY_TRANSFER_FOG(o, o.vertex);
                return o;
            }

            fixed4 frag(v2f i): SV_Target
            {
                fixed4 col = _Color;
                UNITY_APPLY_FOG(i.fogCoord, col);
                UNITY_OPAQUE_ALPHA(col.a);
                return col;
            }
            ENDCG
            
        }
    }
}

#pragma multi_compile_fog

实现很简单，重点点记录

  • #pragma multi_compile_fog
  • UNITY_VERTEX_INPUT_INSTANCE_ID
  • UNITY_FOG_COORDS(0)
  • UNITY_VERTEX_OUTPUT_STEREO
  • UNITY_SETUP_INSTANCE_ID(v)
  • UNITY_INITIALIZE_VERTEX_OUTPUT_STEREO(o)
  • UNITY_TRANSFER_FOG(o, o.vertex)
  • UNITY_APPLY_FOG(i.fogCoord, col)
  • UNITY_OPAQUE_ALPHA(col.a)

这些在一个基础的顶点片元着色器的基本原里。

基础概念宏定义

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#define 标识  //定义标识，如果 （标识） 已经被标识过会报错。
#undef 标识   //取消标识的定义
#ifdef 标识   //判断某个宏是否被定义，若已定义，执行随后的语句
#ifndef 标示  // 判断"标示"是否定义，如果被定义则返回false，如果没有被定义则返回true

#if           //编译预处理中的条件命令，相当于C语法中的if语句
#elif         // 若#if, #ifdef, #ifndef或前面的#elif条件不满足，则执行#elif之后的语句，相当于C语法中的else-if
#else         //与#if, #ifdef, #ifndef对应, 若这些条件不满足，则执行#else之后的语句，相当于C语法中的else
#endif        //#if, #ifdef, #ifndef这些条件命令的结束标志.  
defined(宏)        与#if, #elif配合使用，判断某个宏是否被定义

#include “UnityCG.cginc”

这里需要注意下,include并不是像c++ 这样在调用shader时将文件include进去，而是在编译shader时决定生成的代码。可以测试在去掉#pragma multi_compile_fog前后点击shader面板 Compile and show code 查看编译后的代码。

追到UnityCG.cginc文件中查看UNITY_FOG_COORDS宏

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#if defined(FOG_LINEAR) || defined(FOG_EXP) || defined(FOG_EXP2)
    #define UNITY_FOG_COORDS(idx) UNITY_FOG_COORDS_PACKED(idx, float1)

    #if (SHADER_TARGET < 30) || defined(SHADER_API_MOBILE)
        // mobile or SM2.0: calculate fog factor per-vertex
        #define UNITY_TRANSFER_FOG(o,outpos) UNITY_CALC_FOG_FACTOR((outpos).z); o.fogCoord.x = unityFogFactor
        #define UNITY_TRANSFER_FOG_COMBINED_WITH_TSPACE(o,outpos) UNITY_CALC_FOG_FACTOR((outpos).z); o.tSpace1.y = tangentSign; o.tSpace2.y = unityFogFactor
        #define UNITY_TRANSFER_FOG_COMBINED_WITH_WORLD_POS(o,outpos) UNITY_CALC_FOG_FACTOR((outpos).z); o.worldPos.w = unityFogFactor
        #define UNITY_TRANSFER_FOG_COMBINED_WITH_EYE_VEC(o,outpos) UNITY_CALC_FOG_FACTOR((outpos).z); o.eyeVec.w = unityFogFactor
    #else
        // SM3.0 and PC/console: calculate fog distance per-vertex, and fog factor per-pixel
        #define UNITY_TRANSFER_FOG(o,outpos) o.fogCoord.x = (outpos).z
        #define UNITY_TRANSFER_FOG_COMBINED_WITH_TSPACE(o,outpos) o.tSpace2.y = (outpos).z
        #define UNITY_TRANSFER_FOG_COMBINED_WITH_WORLD_POS(o,outpos) o.worldPos.w = (outpos).z
        #define UNITY_TRANSFER_FOG_COMBINED_WITH_EYE_VEC(o,outpos) o.eyeVec.w = (outpos).z
    #endif
#else
    #define UNITY_FOG_COORDS(idx)
    #define UNITY_TRANSFER_FOG(o,outpos)
    #define UNITY_TRANSFER_FOG_COMBINED_WITH_TSPACE(o,outpos)
    #define UNITY_TRANSFER_FOG_COMBINED_WITH_WORLD_POS(o,outpos)
    #define UNITY_TRANSFER_FOG_COMBINED_WITH_EYE_VEC(o,outpos)
#endif

当开启Fog时 

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#define UNITY_FOG_COORDS(idx) UNITY_FOG_COORDS_PACKED(idx, float1)

UNITY_FOG_COORDS_PACKED

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#define UNITY_FOG_COORDS_PACKED(idx, vectype) vectype fogCoord : TEXCOORD##idx;

可知实际 UNITY_FOG_COORDS(0) 如果Fog开启,相当一在片元数据中定义了

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float1 fogCoord : TEXCOORD0

UNITY_TRANSFER_FOG

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#if defined(FOG_LINEAR) || defined(FOG_EXP) || defined(FOG_EXP2)
    #define UNITY_FOG_COORDS(idx) UNITY_FOG_COORDS_PACKED(idx, float1)

    #if (SHADER_TARGET < 30) || defined(SHADER_API_MOBILE)
        // mobile or SM2.0: calculate fog factor per-vertex
        #define UNITY_TRANSFER_FOG(o,outpos) UNITY_CALC_FOG_FACTOR((outpos).z); o.fogCoord.x = unityFogFactor
        #define UNITY_TRANSFER_FOG_COMBINED_WITH_TSPACE(o,outpos) UNITY_CALC_FOG_FACTOR((outpos).z); o.tSpace1.y = tangentSign; o.tSpace2.y = unityFogFactor
        #define UNITY_TRANSFER_FOG_COMBINED_WITH_WORLD_POS(o,outpos) UNITY_CALC_FOG_FACTOR((outpos).z); o.worldPos.w = unityFogFactor
        #define UNITY_TRANSFER_FOG_COMBINED_WITH_EYE_VEC(o,outpos) UNITY_CALC_FOG_FACTOR((outpos).z); o.eyeVec.w = unityFogFactor
    #else
        // SM3.0 and PC/console: calculate fog distance per-vertex, and fog factor per-pixel
        #define UNITY_TRANSFER_FOG(o,outpos) o.fogCoord.x = (outpos).z
        #define UNITY_TRANSFER_FOG_COMBINED_WITH_TSPACE(o,outpos) o.tSpace2.y = (outpos).z
        #define UNITY_TRANSFER_FOG_COMBINED_WITH_WORLD_POS(o,outpos) o.worldPos.w = (outpos).z
        #define UNITY_TRANSFER_FOG_COMBINED_WITH_EYE_VEC(o,outpos) o.eyeVec.w = (outpos).z
    #endif
#else
    #define UNITY_FOG_COORDS(idx)
    #define UNITY_TRANSFER_FOG(o,outpos)
    #define UNITY_TRANSFER_FOG_COMBINED_WITH_TSPACE(o,outpos)
    #define UNITY_TRANSFER_FOG_COMBINED_WITH_WORLD_POS(o,outpos)
    #define UNITY_TRANSFER_FOG_COMBINED_WITH_EYE_VEC(o,outpos)
#endif

因为 #pragma target 2.0 时 SHADER_TARGET <30 所以

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#if defined(FOG_LINEAR)
    // factor = (end-z)/(end-start) = z * (-1/(end-start)) + (end/(end-start))
    #define UNITY_CALC_FOG_FACTOR_RAW(coord) float unityFogFactor = (coord) * unity_FogParams.z + unity_FogParams.w
#elif defined(FOG_EXP)
    // factor = exp(-density*z)
    #define UNITY_CALC_FOG_FACTOR_RAW(coord) float unityFogFactor = unity_FogParams.y * (coord); unityFogFactor = exp2(-unityFogFactor)
#elif defined(FOG_EXP2)
    // factor = exp(-(density*z)^2)
    #define UNITY_CALC_FOG_FACTOR_RAW(coord) float unityFogFactor = unity_FogParams.x * (coord); unityFogFactor = exp2(-unityFogFactor*unityFogFactor)
#else
    #define UNITY_CALC_FOG_FACTOR_RAW(coord) float unityFogFactor = 0.0
#endif


#define UNITY_CALC_FOG_FACTOR(coord) UNITY_CALC_FOG_FACTOR_RAW(UNITY_Z_0_FAR_FROM_CLIPSPACE(coord))

 #define UNITY_TRANSFER_FOG(o,outpos) UNITY_CALC_FOG_FACTOR((outpos).z); o.fogCoord.x = unityFogFactor

可以追溯宏定义的运算 得到 fogCoord值,并在 UNITY_APPLY_FOG(i.fogCoord, col);得到新得col值。

备注

INSTANCE 和FOG 会在后面补充，这里只记录shader分析的一个过程。

李晨曦Game Developer & U3D,UE4

Game Developer & U3D,UE4