使用Unity Shader的陰影計算宏時需要注意的東西

舊版本

在Unity的舊版本中，根據TRANSFER_SHADOW的宏定義，a2v結構體中的頂點坐標變量名必須是vertex，頂點着色器的輸入結構體a2v必須命名為v，且v2f中的頂點位置變量必須命名為pos。

#if defined (SHADOWS_SCREEN)

    #if defined(UNITY_NO_SCREENSPACE_SHADOWS)
        UNITY_DECLARE_SHADOWMAP(_ShadowMapTexture);
        #define TRANSFER_SHADOW(a) a._ShadowCoord = mul( unity_WorldToShadow[0], mul( unity_ObjectToWorld, v.vertex ) );
        inline fixed unitySampleShadow (unityShadowCoord4 shadowCoord)
        {
            #if defined(SHADOWS_NATIVE)
                fixed shadow = UNITY_SAMPLE_SHADOW(_ShadowMapTexture, shadowCoord.xyz);
                shadow = _LightShadowData.r + shadow * (1-_LightShadowData.r);
                return shadow;
            #else
                unityShadowCoord dist = SAMPLE_DEPTH_TEXTURE(_ShadowMapTexture, shadowCoord.xy);
                // tegra is confused if we use _LightShadowData.x directly
                // with "ambiguous overloaded function reference max(mediump float, float)"
                unityShadowCoord lightShadowDataX = _LightShadowData.x;
                unityShadowCoord threshold = shadowCoord.z;
                return max(dist > threshold, lightShadowDataX);
            #endif
        }

    #else // UNITY_NO_SCREENSPACE_SHADOWS
        UNITY_DECLARE_SCREENSPACE_SHADOWMAP(_ShadowMapTexture);
        #define TRANSFER_SHADOW(a) a._ShadowCoord = ComputeScreenPos(a.pos);
        inline fixed unitySampleShadow (unityShadowCoord4 shadowCoord)
        {
            fixed shadow = UNITY_SAMPLE_SCREEN_SHADOW(_ShadowMapTexture, shadowCoord);
            return shadow;
        }

    #endif

    #define SHADOW_COORDS(idx1) unityShadowCoord4 _ShadowCoord : TEXCOORD##idx1;
    #define SHADOW_ATTENUATION(a) unitySampleShadow(a._ShadowCoord)
#endif

新版本

在Unity的新版本中，使用TRANSFER_SHADOW_CASTER_NORMALOFFSET來計算陰影的紋理坐標，根據其源碼的定義，頂點着色器的輸入結構體a2v必須命名為v，且v2f中的需要有法線變量normal,裁剪空間的位置向量vertex.

#define V2F_SHADOW_CASTER V2F_SHADOW_CASTER_NOPOS UNITY_POSITION(pos)
#if defined(SHADOWS_CUBE) && !defined(SHADOWS_CUBE_IN_DEPTH_TEX)
    // Rendering into point light (cubemap) shadows
    #define V2F_SHADOW_CASTER_NOPOS float3 vec : TEXCOORD0;
    #define TRANSFER_SHADOW_CASTER_NOPOS_LEGACY(o,opos) o.vec = mul(unity_ObjectToWorld, v.vertex).xyz - _LightPositionRange.xyz; opos = UnityObjectToClipPos(v.vertex);
    #define TRANSFER_SHADOW_CASTER_NOPOS(o,opos) o.vec = mul(unity_ObjectToWorld, v.vertex).xyz - _LightPositionRange.xyz; opos = UnityObjectToClipPos(v.vertex);
    #define SHADOW_CASTER_FRAGMENT(i) return UnityEncodeCubeShadowDepth ((length(i.vec) + unity_LightShadowBias.x) * _LightPositionRange.w);

#else
    // Rendering into directional or spot light shadows
    #define V2F_SHADOW_CASTER_NOPOS
    // Let embedding code know that V2F_SHADOW_CASTER_NOPOS is empty; so that it can workaround
    // empty structs that could possibly be produced.
    #define V2F_SHADOW_CASTER_NOPOS_IS_EMPTY
    #define TRANSFER_SHADOW_CASTER_NOPOS_LEGACY(o,opos) \
        opos = UnityObjectToClipPos(v.vertex.xyz); \
        opos = UnityApplyLinearShadowBias(opos);
    #define TRANSFER_SHADOW_CASTER_NOPOS(o,opos) \
        opos = UnityClipSpaceShadowCasterPos(v.vertex, v.normal); \
        opos = UnityApplyLinearShadowBias(opos);
    #define SHADOW_CASTER_FRAGMENT(i) return 0;
#endif