Fix light indexing (#6577)

* Fix light indexing with min16float4.

* Update changelog.

Author: eh-unity

com.unity.render-pipelines.universal/CHANGELOG.md

@@ -18,6 +18,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 - Fixed inspector documentation URLs for the URP asset and Universal Renderer asset.
 - Fixed render scale setting unintentionally affecting the scene view camera.
 - Fixed property wrappers around material properties.
+- Fixed incorrect light indexing on Windows Editor with Android target. [case 1378103](https://issuetracker.unity3d.com/product/unity/issues/guid/1378103/)
 - Fixed missing depth for Depth of Field in an overlay camera. [case 1365623](https://issuetracker.unity3d.com/product/unity/issues/guid/1365623/)
 - Fixed FXAA quality issues when render scale is not 1.0.
 

com.unity.render-pipelines.universal/ShaderLibrary/RealtimeLights.hlsl

@@ -252,7 +252,12 @@ int GetPerObjectLightIndex(uint index)
     // replacing unity_LightIndicesX[i] with a dp4 with identity matrix.
     // u_xlat16_40 = dot(unity_LightIndices[int(u_xlatu13)], ImmCB_0_0_0[u_xlati1]);
     // This increases both arithmetic and register pressure.
-    return int(unity_LightIndices[index / 4][index % 4]);
+    //
+    // NOTE: min16float4 bug workaround.
+    // Take the "vec4" part into float4 tmp variable in order to force float4 math.
+    // It appears indexing half4 as min16float4 on DX11 can fail. (dp4 {min16f})
+    float4 tmp = unity_LightIndices[index / 4];
+    return int(tmp[index % 4]);
 #else
     // Fallback to GLES2. No bitfield magic here :(.
     // We limit to 4 indices per object and only sample unity_4LightIndices0.