Fix for Final Image Histogram debug mode not working on some hardware (#7041)

* fix

* changelog

Co-authored-by: sebastienlagarde <[email protected]>

Author: FrancescoC-unity

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

@@ -121,6 +121,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 - Fixed PBR Dof using the wrong resolution for COC min/max filter, and also using the wrong parameters when running post TAAU stabilization. (case 1388961)
 - Fixed the list of included HDRP asset used for stripping in the build process.
 - Fixed HDRP camera debug panel rendering foldout.
+- Fixed issue with Final Image Histogram displaying a flat histogram on certain GPUs and APIs.
 
 ## [14.0.0] - 2021-11-17
 

com.unity.render-pipelines.high-definition/Runtime/RenderPipeline/HDRenderPipeline.Debug.cs

@@ -880,7 +880,7 @@ void GenerateDebugImageHistogram(RenderGraph renderGraph, HDCamera hdCamera, Tex
 
             using (var builder = renderGraph.AddRenderPass<DebugImageHistogramData>("Generate Debug Image Histogram", out var passData, ProfilingSampler.Get(HDProfileId.FinalImageHistogram)))
             {
-                ValidateComputeBuffer(ref m_DebugImageHistogramBuffer, k_DebugImageHistogramBins * 4, sizeof(uint));
+                ValidateComputeBuffer(ref m_DebugImageHistogramBuffer, k_DebugImageHistogramBins, 4 * sizeof(uint));
                 m_DebugImageHistogramBuffer.SetData(m_EmptyDebugImageHistogram);    // Clear the histogram
 
                 passData.debugImageHistogramCS = defaultResources.shaders.debugImageHistogramCS;