Fix Luminance/EV conversion when LightMeterCalibrationConstant is changed (#6115)

Author: adrien-de-tocqueville

com.unity.render-pipelines.high-definition/CHANGELOG.md

@@ -48,6 +48,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 - Fixed issue with path traced shadows and layer masks (case 1375638).
 - Fixed Z axis orientation when sampling 3D textures in local volumetric fog.
 - Fixed geometry scale issue with the Eye Shader.
+- Fixed light unit conversion after changing mid gray value.
 
 ### Changed
 - Use RayTracingAccelerationStructure.CullInstances to filter Renderers and populate the acceleration structure with ray tracing instances for improved CPU performance on the main thread.

com.unity.render-pipelines.high-definition/Editor/Material/UIBlocks/EmissionUIBlock.cs

@@ -15,7 +15,9 @@ namespace UnityEditor.Rendering.HighDefinition
     /// </summary>
     public class EmissionUIBlock : MaterialUIBlock
     {
-        static float s_MaxEvValue = Mathf.Floor(LightUtils.ConvertLuminanceToEv(float.MaxValue)) - 1;
+        // Max EV Value. Equals to LightUtils.ConvertLuminanceToEv(float.MaxValue)
+        // Literal value to avoid precision issue with max float and to be independent of ColorUtils.s_LightMeterCalibrationConstant.
+        static float s_MaxEvValue = 130.0f;
 
         /// <summary>Options for emission block features. Use this to control which fields are visible.</summary>
         [Flags]

com.unity.render-pipelines.high-definition/Runtime/Lighting/LightUtils.cs

@@ -8,8 +8,8 @@ namespace UnityEngine.Rendering.HighDefinition
     /// </summary>
     class LightUtils
     {
-        static float s_LuminanceToEvFactor = Mathf.Log(100f / ColorUtils.s_LightMeterCalibrationConstant, 2);
-        static float s_EvToLuminanceFactor = -Mathf.Log(100f / ColorUtils.s_LightMeterCalibrationConstant, 2);
+        static float s_LuminanceToEvFactor => Mathf.Log(100f / ColorUtils.s_LightMeterCalibrationConstant, 2);
+        static float s_EvToLuminanceFactor => -Mathf.Log(100f / ColorUtils.s_LightMeterCalibrationConstant, 2);
 
         // Physical light unit helper
         // All light unit are in lumen (Luminous power)