From b0bacc28e0b0d04a2c20a2af3117253e0f29ab3f Mon Sep 17 00:00:00 2001
From: assiduous <assiduous@diligentgraphics.com>
Date: Tue, 7 Jan 2025 19:28:51 -0800
Subject: [PATCH] TemporalAntiAliasing: added GetJitteredProjMatrix helper
 function

---
 Hydrogent/src/Tasks/HnBeginFrameTask.cpp      | 12 ++++-------
 .../interface/TemporalAntiAliasing.hpp        | 21 ++++++++++++++++++-
 2 files changed, 24 insertions(+), 9 deletions(-)

diff --git a/Hydrogent/src/Tasks/HnBeginFrameTask.cpp b/Hydrogent/src/Tasks/HnBeginFrameTask.cpp
index 898c68ba..1b4b1ec7 100644
--- a/Hydrogent/src/Tasks/HnBeginFrameTask.cpp
+++ b/Hydrogent/src/Tasks/HnBeginFrameTask.cpp
@@ -1,5 +1,5 @@
 /*
- *  Copyright 2023-2024 Diligent Graphics LLC
+ *  Copyright 2023-2025 Diligent Graphics LLC
  *
  *  Licensed under the Apache License, Version 2.0 (the "License");
  *  you may not use this file except in compliance with the License.
@@ -40,6 +40,7 @@
 #include "MapHelper.hpp"
 #include "ScopedDebugGroup.hpp"
 #include "GLTF_PBR_Renderer.hpp"
+#include "TemporalAntiAliasing.hpp"
 
 namespace Diligent
 {
@@ -493,10 +494,7 @@ void HnBeginFrameTask::UpdateFrameConstants(IDeviceContext* pCtx,
         PrevCamera = CamAttribs;
         if (m_pCamera != nullptr)
         {
-            float4x4 ProjMatrix = m_pCamera->GetProjectionMatrix();
-            ProjMatrix[2][0]    = Jitter.x;
-            ProjMatrix[2][1]    = Jitter.y;
-
+            const float4x4  ProjMatrix  = TemporalAntiAliasing::GetJitteredProjMatrix(m_pCamera->GetProjectionMatrix(), Jitter);
             const float4x4& ViewMatrix  = m_pCamera->GetViewMatrix();
             const float4x4& WorldMatrix = m_pCamera->GetWorldMatrix();
             const float4x4  ViewProj    = ViewMatrix * ProjMatrix;
@@ -554,9 +552,7 @@ void HnBeginFrameTask::UpdateFrameConstants(IDeviceContext* pCtx,
             }
             else
             {
-                float4x4 PrevProj = PrevCamera.mProj;
-                PrevProj[2][0]    = Jitter.x;
-                PrevProj[2][1]    = Jitter.y;
+                const float4x4 PrevProj = TemporalAntiAliasing::GetJitteredProjMatrix(PrevCamera.mProj, Jitter);
                 if (PrevProj != CamAttribs.mProj)
                 {
                     CameraTransformDirty = true;
diff --git a/PostProcess/TemporalAntiAliasing/interface/TemporalAntiAliasing.hpp b/PostProcess/TemporalAntiAliasing/interface/TemporalAntiAliasing.hpp
index 6dcb328d..f2ee27ac 100644
--- a/PostProcess/TemporalAntiAliasing/interface/TemporalAntiAliasing.hpp
+++ b/PostProcess/TemporalAntiAliasing/interface/TemporalAntiAliasing.hpp
@@ -1,5 +1,5 @@
 /*
- *  Copyright 2024 Diligent Graphics LLC
+ *  Copyright 2024-2025 Diligent Graphics LLC
  *
  *  Licensed under the Apache License, Version 2.0 (the "License");
  *  you may not use this file except in compliance with the License.
@@ -116,6 +116,25 @@ class TemporalAntiAliasing
 
     ITextureView* GetAccumulatedFrameSRV(bool IsPrevFrame = false, Uint32 AccumulationBufferIdx = 0) const;
 
+    static inline float4x4 GetJitteredProjMatrix(float4x4 Proj, const float2& Jitter)
+    {
+        if (Proj.m33 == 0.f)
+        {
+            // Perspective projection.
+            // Make jitter proportional to z so that it is constant in screen space.
+            Proj.m20 += Jitter.x;
+            Proj.m21 += Jitter.y;
+        }
+        else
+        {
+            // Orthographic projection.
+            // Apply offsets directly.
+            Proj.m30 += Jitter.x;
+            Proj.m31 += Jitter.y;
+        }
+        return Proj;
+    }
+
 private:
     using RenderTechnique  = PostFXRenderTechnique;
     using ResourceInternal = RefCntAutoPtr<IDeviceObject>;