Changed FullScreenTrianglePass::FrameBegin to use FramePrepareParams viewport and scissor states if they are set.

Changed ReflectionScreenSpaceBlurChildPass to set the viewport and scissor states.

Gems/Atom/Feature/Common/Code/Source/ReflectionScreenSpace/ReflectionScreenSpaceBlurChildPass.cpp

@@ -47,6 +47,9 @@ namespace AZ
                 m_updateSrg = true;
             }
 
+            params.m_viewportState = RHI::Viewport(0, static_cast<float>(m_imageSize.m_width), 0, static_cast<float>(m_imageSize.m_height));
+            params.m_scissorState = RHI::Scissor(0, 0, m_imageSize.m_width, m_imageSize.m_height);
+
             FullscreenTrianglePass::FrameBeginInternal(params);
         }
 

Gems/Atom/RPI/Code/Source/RPI.Public/Pass/FullscreenTrianglePass.cpp

@@ -181,9 +181,19 @@ namespace AZ
 
             RHI::Size targetImageSize = outputAttachment->m_descriptor.m_image.m_size;
 
-            // Base viewport and scissor off of target attachment
+            m_viewportState = params.m_viewportState;
+            if (m_viewportState.IsNull())
+            {
+                // compute viewport from target attachment
                 m_viewportState = RHI::Viewport(0, static_cast<float>(targetImageSize.m_width), 0, static_cast<float>(targetImageSize.m_height));
+            }
+
+            m_scissorState = params.m_scissorState;
+            if (m_scissorState.IsNull())
+            {
+                // compute scissor from target attachment
                 m_scissorState = RHI::Scissor(0, 0, targetImageSize.m_width, targetImageSize.m_height);
+            }
 
             RenderPass::FrameBeginInternal(params);
         }