From 596ad18ce360aa0e5aad53685e9b7edf19474269 Mon Sep 17 00:00:00 2001
From: Wojtek Figat <wojtek@figat.pl>
Date: Mon, 12 Aug 2024 18:32:33 +0200
Subject: [PATCH] Add smooth light brightness fade out at last 10% of
 `ViewDistance` (if used)

---
 Source/Engine/Level/Actors/DirectionalLight.cpp |  4 ++--
 Source/Engine/Level/Actors/Light.h              | 15 ++++++++++++++-
 Source/Engine/Level/Actors/PointLight.cpp       |  4 ++--
 Source/Engine/Level/Actors/SpotLight.cpp        |  4 ++--
 4 files changed, 20 insertions(+), 7 deletions(-)

diff --git a/Source/Engine/Level/Actors/DirectionalLight.cpp b/Source/Engine/Level/Actors/DirectionalLight.cpp
index 97f9c3b58..5e52b4e74 100644
--- a/Source/Engine/Level/Actors/DirectionalLight.cpp
+++ b/Source/Engine/Level/Actors/DirectionalLight.cpp
@@ -18,11 +18,11 @@ void DirectionalLight::Draw(RenderContext& renderContext)
 {
     float brightness = Brightness;
     AdjustBrightness(renderContext.View, brightness);
-    const Float3 position = GetPosition() - renderContext.View.Origin;
+    Float3 position;
     if (Brightness > ZeroTolerance
         && EnumHasAnyFlags(renderContext.View.Flags, ViewFlags::DirectionalLights)
         && EnumHasAnyFlags(renderContext.View.Pass, DrawPass::GBuffer)
-        && (ViewDistance < ZeroTolerance || Float3::DistanceSquared(renderContext.View.Position, position) < ViewDistance * ViewDistance))
+        && CheckViewDistance(renderContext.View.Position, renderContext.View.Origin, position, brightness))
     {
         RenderDirectionalLightData data;
         data.Position = position;
diff --git a/Source/Engine/Level/Actors/Light.h b/Source/Engine/Level/Actors/Light.h
index 9c3d6ff73..3138d996f 100644
--- a/Source/Engine/Level/Actors/Light.h
+++ b/Source/Engine/Level/Actors/Light.h
@@ -29,7 +29,7 @@ public:
     float Brightness = 3.14f;
 
     /// <summary>
-    /// Controls light visibility range. The distance at which the light becomes completely faded. Use a value of 0 to always draw light.
+    /// Controls light visibility range. The distance at which the light becomes completely faded (blend happens on the last 10% of that range). Use a value of 0 to always draw light.
     /// </summary>
     API_FIELD(Attributes="EditorOrder(35), Limit(0, float.MaxValue, 10.0f), EditorDisplay(\"Light\")")
     float ViewDistance = 0.0f;
@@ -56,6 +56,19 @@ protected:
     // Adjust the light brightness used during rendering (called by light types inside SetupLightData callback)
     void AdjustBrightness(const RenderView& view, float& brightness) const;
 
+    FORCE_INLINE bool CheckViewDistance(const Float3& viewPosition, const Float3& viewOrigin, Float3& position, float& brightness) const
+    {
+        position = _transform.Translation - viewOrigin;
+        if (ViewDistance > ZeroTolerance)
+        {
+            const float dst2 = Vector3::DistanceSquared(viewPosition, position);
+            const float dst = Math::Sqrt(dst2);
+            brightness *= Math::Remap(dst, 0.9f * ViewDistance, ViewDistance, 1.0f, 0.0f);
+            return dst < ViewDistance;
+        }
+        return true;
+    }
+
 public:
     // [Actor]
     void OnEnable() override;
diff --git a/Source/Engine/Level/Actors/PointLight.cpp b/Source/Engine/Level/Actors/PointLight.cpp
index 3c85be612..fbe3fd9e6 100644
--- a/Source/Engine/Level/Actors/PointLight.cpp
+++ b/Source/Engine/Level/Actors/PointLight.cpp
@@ -82,13 +82,13 @@ void PointLight::Draw(RenderContext& renderContext)
 {
     float brightness = ComputeBrightness();
     AdjustBrightness(renderContext.View, brightness);
-    const Float3 position = GetPosition() - renderContext.View.Origin;
+    Float3 position;
     const float radius = GetScaledRadius();
     if (EnumHasAnyFlags(renderContext.View.Flags, ViewFlags::PointLights)
         && EnumHasAnyFlags(renderContext.View.Pass, DrawPass::GBuffer)
         && brightness > ZeroTolerance
         && radius > ZeroTolerance
-        && (ViewDistance < ZeroTolerance || Vector3::DistanceSquared(renderContext.View.Position, position) < ViewDistance * ViewDistance))
+        && CheckViewDistance(renderContext.View.Position, renderContext.View.Origin, position, brightness))
     {
         RenderPointLightData data;
         data.Position = position;
diff --git a/Source/Engine/Level/Actors/SpotLight.cpp b/Source/Engine/Level/Actors/SpotLight.cpp
index 38457c94e..9494c14fa 100644
--- a/Source/Engine/Level/Actors/SpotLight.cpp
+++ b/Source/Engine/Level/Actors/SpotLight.cpp
@@ -130,7 +130,7 @@ void SpotLight::Draw(RenderContext& renderContext)
 {
     float brightness = ComputeBrightness();
     AdjustBrightness(renderContext.View, brightness);
-    const Float3 position = GetPosition() - renderContext.View.Origin;
+    Float3 position;
     const float radius = GetScaledRadius();
     const float outerConeAngle = GetOuterConeAngle();
     if (EnumHasAnyFlags(renderContext.View.Flags, ViewFlags::SpotLights)
@@ -138,7 +138,7 @@ void SpotLight::Draw(RenderContext& renderContext)
         && brightness > ZeroTolerance
         && radius > ZeroTolerance
         && outerConeAngle > ZeroTolerance
-        && (ViewDistance < ZeroTolerance || Vector3::DistanceSquared(renderContext.View.Position, position) < ViewDistance * ViewDistance))
+        && CheckViewDistance(renderContext.View.Position, renderContext.View.Origin, position, brightness))
     {
         RenderSpotLightData data;
         data.Position = position;