From ef240ce9860b9c8fcab5f5927450effda4bf7492 Mon Sep 17 00:00:00 2001
From: Wojtek Figat <wojtek@figat.pl>
Date: Mon, 18 Jan 2021 15:53:15 +0100
Subject: [PATCH] Add culling for decals (via DrawMinScreenSize property)

---
 Source/Engine/Level/Actors/Decal.cpp | 10 ++++++++++
 Source/Engine/Level/Actors/Decal.h   |  8 +++++++-
 2 files changed, 17 insertions(+), 1 deletion(-)

diff --git a/Source/Engine/Level/Actors/Decal.cpp b/Source/Engine/Level/Actors/Decal.cpp
index 92652ea7d..c7e8475b3 100644
--- a/Source/Engine/Level/Actors/Decal.cpp
+++ b/Source/Engine/Level/Actors/Decal.cpp
@@ -7,6 +7,7 @@
 #include "Engine/Level/Scene/SceneRendering.h"
 #include "Engine/Graphics/RenderView.h"
 #include "Engine/Graphics/RenderTask.h"
+#include "Engine/Graphics/RenderTools.h"
 
 Decal::Decal(const SpawnParams& params)
     : Actor(params)
@@ -66,6 +67,13 @@ void Decal::Draw(RenderContext& renderContext)
         Material->IsLoaded() &&
         Material->IsDecal())
     {
+        const auto lodView = (renderContext.LodProxyView ? renderContext.LodProxyView : &renderContext.View);
+        const float screenRadiusSquared = RenderTools::ComputeBoundsScreenRadiusSquared(_sphere.Center, _sphere.Radius, *lodView) * renderContext.View.ModelLODDistanceFactorSqrt;
+
+        // Check if decal is being culled
+        if (Math::Square(DrawMinScreenSize * 0.5f) > screenRadiusSquared)
+            return;
+
         renderContext.List->Decals.Add(this);
     }
 }
@@ -80,6 +88,7 @@ void Decal::Serialize(SerializeStream& stream, const void* otherObj)
     SERIALIZE(Material);
     SERIALIZE_MEMBER(Size, _size);
     SERIALIZE(SortOrder);
+    SERIALIZE(DrawMinScreenSize);
 }
 
 void Decal::Deserialize(DeserializeStream& stream, ISerializeModifier* modifier)
@@ -90,6 +99,7 @@ void Decal::Deserialize(DeserializeStream& stream, ISerializeModifier* modifier)
     DESERIALIZE(Material);
     DESERIALIZE_MEMBER(Size, _size);
     DESERIALIZE(SortOrder);
+    DESERIALIZE(DrawMinScreenSize);
 }
 
 bool Decal::IntersectsItself(const Ray& ray, float& distance, Vector3& normal)
diff --git a/Source/Engine/Level/Actors/Decal.h b/Source/Engine/Level/Actors/Decal.h
index 41a5addea..78a92bfd6 100644
--- a/Source/Engine/Level/Actors/Decal.h
+++ b/Source/Engine/Level/Actors/Decal.h
@@ -30,9 +30,15 @@ public:
     /// <summary>
     /// The decal rendering order. The higher values are render later (on top).
     /// </summary>
-    API_FIELD(Attributes="EditorOrder(20), DefaultValue(0), EditorDisplay(\"Decal\")")
+    API_FIELD(Attributes="EditorOrder(20), EditorDisplay(\"Decal\")")
     int32 SortOrder = 0;
 
+    /// <summary>
+    /// The minimum screen size for the decal drawing. If the decal size on the screen is smaller than this value then decal will be culled. Set it to higher value to make culling more aggressive.
+    /// </summary>
+    API_FIELD(Attributes="EditorOrder(30), EditorDisplay(\"Decal\")")
+    float DrawMinScreenSize = 0.02f;
+
     /// <summary>
     /// Gets the decal bounds size (in local space).
     /// </summary>