Fix for sampling garbage outside of screen with low res transparent upsample and dynamic resolution (#6957)

* Fix

* changelog

Co-authored-by: sebastienlagarde <sebastien@unity3d.com>

Author: FrancescoC-unity

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

@@ -103,6 +103,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 - Fixed vertex color mode Add name whicgh was misleading, renamed to AddSubstract.
 - Fixed screen space shadow when multiple lights cast shadows.
 - Fixed issue with accumulation motion blur and depth of field when path tracing is enabled.
+- Fixed issue with dynamic resolution and low res transparency sampling garbage outside of the render target.
 
 ## [14.0.0] - 2021-11-17
 

com.unity.render-pipelines.high-definition/Runtime/ShaderLibrary/UpsampleTransparent.shader

@@ -97,7 +97,9 @@ Shader "Hidden/HDRP/UpsampleTransparent"
 #if DEBUG_EDGE
                 return float4(0.0, 10.0, 0.0, 1.0);
 #else
-                return SAMPLE_TEXTURE2D_X_LOD(_LowResTransparent, s_point_clamp_sampler, ClampAndScaleUVForPoint(nearestUV), 0);
+                // Important note! The reason we need to do ClampAndScaleUVForBilinear is because the candidate for nearestUV are going to be the ones
+                // used for bilinear. We are using the same UVs used for bilinear -hence the uv clamp for bilinear- it is just the filtering that is different.
+                return SAMPLE_TEXTURE2D_X_LOD(_LowResTransparent, s_point_clamp_sampler, ClampAndScaleUVForBilinear(nearestUV), 0);
 #endif
             }
         #else // BILINEAR