From 35d46e23a82b221d0427b33e47c8fb610a947d82 Mon Sep 17 00:00:00 2001
From: Ari Vuollet <ari.vuollet@kapsi.fi>
Date: Sat, 13 Jul 2024 15:52:57 +0300
Subject: [PATCH] Fix `CharacterController::SimpleMove` gravity displacement
 handling

---
 .../Physics/Colliders/CharacterController.cpp     | 15 +++++++++++----
 .../Physics/Colliders/CharacterController.h       |  1 +
 2 files changed, 12 insertions(+), 4 deletions(-)

diff --git a/Source/Engine/Physics/Colliders/CharacterController.cpp b/Source/Engine/Physics/Colliders/CharacterController.cpp
index 3561da8f2..4a4452fc2 100644
--- a/Source/Engine/Physics/Colliders/CharacterController.cpp
+++ b/Source/Engine/Physics/Colliders/CharacterController.cpp
@@ -19,6 +19,7 @@ CharacterController::CharacterController(const SpawnParams& params)
     , _minMoveDistance(0.0f)
     , _isUpdatingTransform(false)
     , _upDirection(Vector3::Up)
+    , _gravityDisplacement(Vector3::Zero)
     , _nonWalkableMode(NonWalkableModes::PreventClimbing)
     , _lastFlags(CollisionFlags::None)
 {
@@ -148,10 +149,16 @@ CharacterController::CollisionFlags CharacterController::GetFlags() const
 CharacterController::CollisionFlags CharacterController::SimpleMove(const Vector3& speed)
 {
     const float deltaTime = Time::GetCurrentSafe()->DeltaTime.GetTotalSeconds();
-    Vector3 displacement = speed;
-    displacement += GetPhysicsScene()->GetGravity() * deltaTime;
-    displacement *= deltaTime;
-    return Move(displacement);
+    Vector3 displacement = speed + _gravityDisplacement;
+    CollisionFlags result = Move(displacement * deltaTime);
+    if ((static_cast<int>(result) & static_cast<int>(CollisionFlags::Below)) != 0)
+    {
+        // Reset accumulated gravity acceleration when we touch the ground
+        _gravityDisplacement = Vector3::Zero;
+    }
+    else
+        _gravityDisplacement += GetPhysicsScene()->GetGravity() * deltaTime;
+    return result;
 }
 
 CharacterController::CollisionFlags CharacterController::Move(const Vector3& displacement)
diff --git a/Source/Engine/Physics/Colliders/CharacterController.h b/Source/Engine/Physics/Colliders/CharacterController.h
index 545f4e9d9..540adc5c9 100644
--- a/Source/Engine/Physics/Colliders/CharacterController.h
+++ b/Source/Engine/Physics/Colliders/CharacterController.h
@@ -66,6 +66,7 @@ private:
     float _minMoveDistance;
     bool _isUpdatingTransform;
     Vector3 _upDirection;
+    Vector3 _gravityDisplacement;
     NonWalkableModes _nonWalkableMode;
     CollisionFlags _lastFlags;