From 429f8e5336bec5bd4f4deaf1921971c32416b8c2 Mon Sep 17 00:00:00 2001
From: Wojtek Figat <wojtek@figat.pl>
Date: Mon, 4 May 2026 16:43:41 +0200
Subject: [PATCH] Add highlight to Motion Vectors Debug view for better content
 optimizing

---
 Content/Shaders/MotionBlur.flax           |  4 ++--
 Source/Engine/Renderer/MotionBlurPass.cpp | 23 +++++++++++++++++++++++
 Source/Engine/Renderer/Renderer.cpp       |  3 ---
 Source/Shaders/MotionBlur.shader          | 20 ++++++++++++++++++--
 4 files changed, 43 insertions(+), 7 deletions(-)

diff --git a/Content/Shaders/MotionBlur.flax b/Content/Shaders/MotionBlur.flax
index c89597a39..2e978818a 100644
--- a/Content/Shaders/MotionBlur.flax
+++ b/Content/Shaders/MotionBlur.flax
@@ -1,3 +1,3 @@
 version https://git-lfs.github.com/spec/v1
-oid sha256:ed42ed126bad47e824e8ac214afc4f6c6be841500b6a9cd845fa8eaf37295c45
-size 9513
+oid sha256:a029dd95886dbb390749163f3c1d1e5cdf6786ee6b65f0e647d231f5c3555ccb
+size 10184
diff --git a/Source/Engine/Renderer/MotionBlurPass.cpp b/Source/Engine/Renderer/MotionBlurPass.cpp
index d0c09debc..910ced532 100644
--- a/Source/Engine/Renderer/MotionBlurPass.cpp
+++ b/Source/Engine/Renderer/MotionBlurPass.cpp
@@ -236,20 +236,43 @@ void MotionBlurPass::RenderMotionVectors(RenderContext& renderContext)
 
 void MotionBlurPass::RenderDebug(RenderContext& renderContext, GPUTextureView* frame)
 {
+    auto outputView = renderContext.Task->GetOutputView();
+    auto outputViewport = renderContext.Task->GetOutputViewport();
     auto context = GPUDevice::Instance->GetMainContext();
     const auto motionVectors = renderContext.Buffers->MotionVectors;
+    context->ResetRenderTarget();
     if (!motionVectors || !motionVectors->IsAllocated() || checkIfSkipPass())
     {
+        context->SetRenderTarget(outputView);
+        context->SetViewportAndScissors(outputViewport);
         context->Draw(frame);
         return;
     }
 
+    // Draw depth of objects that draw motion vectors for better debugging content when optimizing this pass
+    auto desc = GPUTextureDescription::New2D(motionVectors->Width(), motionVectors->Height(), PixelFormat::D16_UNorm, GPUTextureFlags::ShaderResource | GPUTextureFlags::DepthStencil);
+    auto motionObjectsDepth = RenderTargetPool::Get(desc);
+    {
+        PROFILE_GPU_CPU("Motion Vectors Depth");
+        context->SetRenderTarget(motionObjectsDepth->View(), nullptr);
+        context->SetViewportAndScissors((float)desc.Width, (float)desc.Height);
+        context->ClearDepth(motionObjectsDepth->View());
+        renderContext.View.Pass = DrawPass::Depth;
+        renderContext.List->ExecuteDrawCalls(renderContext, DrawCallsListType::MotionVectors);
+        context->ResetRenderTarget();
+    }
+
     PROFILE_GPU_CPU("Motion Vectors Debug");
     context->BindSR(0, frame);
     context->BindSR(1, renderContext.Buffers->MotionVectors->View());
+    context->BindSR(2, motionObjectsDepth->View());
     context->SetState(_psMotionVectorsDebug);
+    context->SetRenderTarget(outputView);
+    context->SetViewportAndScissors(outputViewport);
     context->DrawFullscreenTriangle();
     context->ResetSR();
+
+    RenderTargetPool::Release(motionObjectsDepth);
 }
 
 void MotionBlurPass::Render(RenderContext& renderContext, GPUTexture*& frame, GPUTexture*& tmp)
diff --git a/Source/Engine/Renderer/Renderer.cpp b/Source/Engine/Renderer/Renderer.cpp
index a1f531ac1..0a859d161 100644
--- a/Source/Engine/Renderer/Renderer.cpp
+++ b/Source/Engine/Renderer/Renderer.cpp
@@ -789,9 +789,6 @@ void RenderInner(SceneRenderTask* task, RenderContext& renderContext, RenderCont
     // Debug motion vectors
     if (renderContext.View.Mode == ViewMode::MotionVectors)
     {
-        context->ResetRenderTarget();
-        context->SetRenderTarget(task->GetOutputView());
-        context->SetViewportAndScissors(outputViewport);
         MotionBlurPass::Instance()->RenderDebug(renderContext, frameBuffer->View());
         RenderTargetPool::Release(tempBuffer);
         RenderTargetPool::Release(frameBuffer);
diff --git a/Source/Shaders/MotionBlur.shader b/Source/Shaders/MotionBlur.shader
index 1b33210d0..e190cdd74 100644
--- a/Source/Shaders/MotionBlur.shader
+++ b/Source/Shaders/MotionBlur.shader
@@ -71,10 +71,26 @@ float4 MotionVectorToColor(float2 v)
 META_PS(true, FEATURE_LEVEL_ES2)
 float4 PS_MotionVectorsDebug(Quad_VS2PS input) : SV_Target
 {
-	float4 c = SAMPLE_RT(Input0, input.TexCoord);
+	float4 color = SAMPLE_RT(Input0, input.TexCoord);
+
+    // Grey-out background pixels (that don't draw dedicated motion vectors)
+    float motionObjectsDepth = SAMPLE_RT_DEPTH(Input2, input.TexCoord);
+#if REVERSE_Z
+    bool isBackground = motionObjectsDepth <= 0;
+#else
+    bool isBackground = motionObjectsDepth >= 1;
+#endif
+    uint2 checkerboardCoord = (uint2(input.Position.xy) >> 3) & 0x1;
+    float checkerboard = checkerboardCoord.x == checkerboardCoord.y ? 1.0f : 0.0f;
+    float3 backgroundColor = Luminance(color.rgb).xxx * (0.4f + 0.1f * checkerboard);
+    color.rgb = select(isBackground, backgroundColor, max(color.rgb, 0.2f));
+
+    // Debug color based on the pixel motion
     float2 v = SAMPLE_RT(Input1, input.TexCoord).xy * 20.0f;
     float4 vC = MotionVectorToColor(v);
-    return float4(lerp(c.rgb, vC.rgb, vC.a * 0.6f), c.a);
+    color.rgb =  lerp(color.rgb, vC.rgb, vC.a * 0.6f);
+
+    return color;
 }
 
 // Returns the longer velocity vector