ue4 lightmap的解码

一. lq的解码过程     lightmapCommon.ush   GetLightMapColorLQ()函数：

1. 纹理采样：

 2. 亮度、颜色还原

 3. 还原亮度

 4. 还原最大贡献方向

 5. 最终颜色还原

 二、 hq解码过程  lightmapCommon.ush   GetLightMapColorHQ()函数

1. 纹理采样：分为有vt和没有vt：

 2. 亮度还原

 3. 颜色还原

 4. 还原方向，是否定义方向，是否是双向植被：

 5. 最终颜色：

 三、 skyOcclusion和aomaterialMask的解码

float4 GetSkyBentNormalAndOcclusion(VTPageTableResult LightmapVTPageTableResult, float2 LightmapUV, uint LightmapDataIndex, float2 SvPositionXY)
{
	float4 TextureValue;
#if LIGHTMAP_VT_ENABLED
	TextureValue = SampleLightmapVT( LightmapVTPageTableResult, 3u, LightmapDataIndex, LightmapResourceCluster.VTSkyOcclusionTexture, LIGHTMAP_SHARED_SAMPLER(SkyOcclusionSampler)); 
#else
	TextureValue = Texture2DSample( LightmapResourceCluster.SkyOcclusionTexture, LIGHTMAP_SHARED_SAMPLER(SkyOcclusionSampler), LightmapUV );
#endif

	// Unpack vector
	TextureValue.rgb = TextureValue.rgb * 2 - 1;
	// Undo sqrt which allocated more precision toward 0
	TextureValue.a = TextureValue.a * TextureValue.a;
	return TextureValue;
}

float GetAOMaterialMask(VTPageTableResult LightmapVTPageTableResult, float2 LightmapUV, uint LightmapDataIndex, float2 SvPositionXY)
{
	float TextureValue;
#if LIGHTMAP_VT_ENABLED
	TextureValue = SampleLightmapVT( LightmapVTPageTableResult, 4u, LightmapDataIndex, LightmapResourceCluster.VTAOMaterialMaskTexture, LIGHTMAP_SHARED_SAMPLER(AOMaterialMaskSampler)).x; 
#else
	TextureValue = Texture2DSample( LightmapResourceCluster.AOMaterialMaskTexture, LIGHTMAP_SHARED_SAMPLER(AOMaterialMaskSampler), LightmapUV ).x;
#endif

	// Undo sqrt which allocated more precision toward 0
	return TextureValue * TextureValue;
}

　　

四、 ue4 lightmap编码特点的思考：

1. 好处：

 2. 不足：