Unity Shader Example 8 (光照贴图)

Shader "LightMap"{    Properties {        _Color ("Main Color", Color) = (1, 1, 1, 1)        _MainTex ("Base (RGB)", 2D) = "white" {}        _LightMap ("Lightmap (RGB)", 2D) = "white" {}    }    SubShader {        Tags { "RenderType"="Opaque" }        LOD 200        Pass {            CGPROGRAM            #pragma vertex vert            #pragma fragment frag            #include "UnityCG.cginc"            fixed4 _Color;            float4 _MainTex_ST;            float4 _LightMap_ST;            sampler2D _MainTex;            sampler2D _LightMap;            struct appdata_t {                float4 vertex : POSITION;                fixed4 color : COLOR;                float2 texcoord : TEXCOORD0;                float2 texcoord1 : TEXCOORD1;            };            struct v2f {                float4 vertex : POSITION;                float2 texcoord : TEXCOORD0;                float2 texcoord1 : TEXCOORD1;            };            v2f vert (appdata_t v)            {                v2f o;                o.vertex = mul(UNITY_MATRIX_MVP, v.vertex);                o.texcoord = TRANSFORM_TEX(v.texcoord, _MainTex);                o.texcoord1 = TRANSFORM_TEX(v.texcoord1, _LightMap);                return o;            }            fixed4 frag (v2f i) : COLOR            {                fixed4 c = _Color * tex2D(_MainTex, i.texcoord);                c.rgb *= DecodeLightmap(tex2D(_LightMap, i.texcoord1));                return c;            }            ENDCG        }    }}

参考：

#define TRANSFORM_TEX(tex,name) (tex.xy * name##_ST.xy + name##_ST.zw)

// Decodes HDR textures// handles dLDR, RGBM formats// Called by DecodeLightmap when UNITY_NO_RGBM is not defined.inline half3 DecodeLightmapRGBM (half4 data, half4 decodeInstructions){// If Linear mode is not supported we can skip exponent part#if defined(UNITY_NO_LINEAR_COLORSPACE)# if defined(UNITY_FORCE_LINEAR_READ_FOR_RGBM)return (decodeInstructions.x * data.a) * sqrt(data.rgb);# elsereturn (decodeInstructions.x * data.a) * data.rgb;# endif#elsereturn (decodeInstructions.x * pow(data.a, decodeInstructions.y)) * data.rgb;#endif}// Decodes doubleLDR encoded lightmaps.inline half3 DecodeLightmapDoubleLDR( fixed4 color ){return 2.0 * color.rgb;}half4 unity_Lightmap_HDR;inline half3 DecodeLightmap( fixed4 color ){#if defined(UNITY_NO_RGBM)return DecodeLightmapDoubleLDR( color );#elsereturn DecodeLightmapRGBM( color, unity_Lightmap_HDR );#endif}

解析：

o.texcoord1 = TRANSFORM_TEX(v.texcoord1, _LightMap); == o.texcoord1  = v.texcoord1.xy * _LightMap_ST.xy + _LightMap_ST.zw

对于GamePlay：

在.vert文件中

#if defined(LIGHTMAP)v_texCoord1 = a_texCoord1 * u_lightmapTextureST.xy + u_lightmapTextureST.zw;#endif

在.frag文件中

<pre class="plain" name="code">#if defined(LIGHTMAP)vec4 lightColor = texture2D(u_lightmapTexture, v_texCoord1);gl_FragColor.rgb *= lightColor.rgb;#endif

理解uv2：

uv2就类似uv，uv2是在建模的时候确定的（unity里面可以自动生成，相当于在模型中建立uv2)。

在生成光照贴图的时候，会根据顶点的uv2来生成。

理解Unity3D的Lightmap的Scale和Offset：

The UV scale & offset used for a lightmap.

A lightmap is a texture atlas and multiple Renderers can use different portions of the same lightmap.The vector's x and y refer to UV scale, while z and w refer to UV offset.

补充：

更换光照贴图

 mat.SetTexture("_LightMap", lightMap); mat.SetTextureScale("_LightMap", new Vector2(scaleOffset.x, scaleOffset.y)); mat.SetTextureOffset("_LightMap", new Vector2(scaleOffset.z, scaleOffset.w));