Apply SSAO term to LW Standard

ScriptableRenderPipeline/LightweightPipeline/LWRP/ShaderLibrary/Core.hlsl

     ApplyFogColor(color, unity_FogColor.rgb, fogFactor);
 }
 
+void ApplySSAO(inout half occlusion, float4 texcoord)
+{
+    half ssao = 1.0 - SAMPLE_TEXTURE2D(_AmbientOcclusion, sampler_AmbientOcclusion, texcoord.xy / texcoord.w);
+    
+    //TODO: The occlusion term is only a half, breaking colored AO.
+    //TODO: Find better occlusion mix method.
+    occlusion *= lerp(_AmbientOcclusionParam.rgb, float3(1.0, 1.0, 1.0), ssao); 
+}
+
 // Stereo-related bits
 #if defined(UNITY_STEREO_INSTANCING_ENABLED) || defined(UNITY_STEREO_MULTIVIEW_ENABLED)
     #define SCREENSPACE_TEXTURE TEXTURE2D_ARRAY

ScriptableRenderPipeline/LightweightPipeline/LWRP/ShaderLibrary/Input.hlsl

 half4 _AdditionalLightDistanceAttenuation[MAX_VISIBLE_LIGHTS];
 half4 _AdditionalLightSpotDir[MAX_VISIBLE_LIGHTS];
 half4 _AdditionalLightSpotAttenuation[MAX_VISIBLE_LIGHTS];
+
+half4 _AmbientOcclusionParam;
+
+TEXTURE2D(_AmbientOcclusion);
+SAMPLER(sampler_AmbientOcclusion);
 
 #define UNITY_MATRIX_M     unity_ObjectToWorld
 #define UNITY_MATRIX_I_M   unity_WorldToObject

ScriptableRenderPipeline/LightweightPipeline/LWRP/ShaderLibrary/LightweightPassLit.hlsl

 
     SurfaceData surfaceData;
     InitializeStandardLitSurfaceData(IN.uv, surfaceData);
+    ApplySSAO(surfaceData.occlusion, IN.shadowCoord); //The shadowcoord is the screen space position.
-
 
     half4 color = LightweightFragmentPBR(inputData, surfaceData.albedo, surfaceData.metallic, surfaceData.specular, surfaceData.smoothness, surfaceData.occlusion, surfaceData.emission, surfaceData.alpha);