From 0d9af9f200dba07e4d5bcf622958486734fc112b Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Tur=C3=A1nszki=20J=C3=A1nos?=
 <turanszkij@users.noreply.github.com>
Date: Mon, 11 Apr 2022 09:32:59 +0200
Subject: [PATCH] Grass interaction (#413)

* hairparticle simulation clamping

* editor: hair particle interaction

* update
---
 Editor/Editor.cpp                             | 21 +++++++++++++++++++
 Editor/Editor.h                               |  1 +
 .../shaders/hairparticle_simulateCS.hlsl      | 11 +++++++---
 3 files changed, 30 insertions(+), 3 deletions(-)

diff --git a/Editor/Editor.cpp b/Editor/Editor.cpp
index 185d861fb..050ffa715 100644
--- a/Editor/Editor.cpp
+++ b/Editor/Editor.cpp
@@ -1124,6 +1124,11 @@ void EditorComponent::Update(float dt)
 	Scene& scene = wi::scene::GetScene();
 	CameraComponent& camera = wi::scene::GetCamera();
 
+	if (scene.forces.Contains(grass_interaction_entity))
+	{
+		scene.Entity_Remove(grass_interaction_entity);
+	}
+
 	cameraWnd.Update();
 	animWnd.Update();
 	weatherWnd.Update();
@@ -1501,6 +1506,22 @@ void EditorComponent::Update(float dt)
 					}
 				}
 
+				if (scene.hairs.Contains(hovered.entity))
+				{
+					XMVECTOR P = XMLoadFloat3(&hovered.position);
+					P += XMLoadFloat3(&hovered.normal) * 2;
+					if (grass_interaction_entity == INVALID_ENTITY)
+					{
+						grass_interaction_entity = CreateEntity();
+					}
+					ForceFieldComponent& force = scene.forces.Create(grass_interaction_entity);
+					TransformComponent& transform = scene.transforms.Create(grass_interaction_entity);
+					force.type = ENTITY_TYPE_FORCEFIELD_POINT;
+					force.gravity = -80;
+					force.range_local = 3;
+					transform.Translate(P);
+				}
+
 			}
 		}
 
diff --git a/Editor/Editor.h b/Editor/Editor.h
index 8326fad9c..85f05dca4 100644
--- a/Editor/Editor.h
+++ b/Editor/Editor.h
@@ -151,6 +151,7 @@ public:
 
 	Translator translator;
 	wi::scene::PickResult hovered;
+	wi::ecs::Entity grass_interaction_entity = wi::ecs::INVALID_ENTITY;
 
 	void ClearSelected();
 	void AddSelected(wi::ecs::Entity entity);
diff --git a/WickedEngine/shaders/hairparticle_simulateCS.hlsl b/WickedEngine/shaders/hairparticle_simulateCS.hlsl
index ca41018bc..a8ebdb40b 100644
--- a/WickedEngine/shaders/hairparticle_simulateCS.hlsl
+++ b/WickedEngine/shaders/hairparticle_simulateCS.hlsl
@@ -159,9 +159,14 @@ void main(uint3 DTid : SV_DispatchThreadID, uint3 Gid : SV_GroupID, uint groupIn
 		velocity += surface_velocity;
 
 		// Apply forces:
-		velocity += force;
-		normal += velocity * delta_time;
-		normal = normalize(normal);
+		float3 newVelocity = velocity + force;
+		float3 newNormal = normal + newVelocity * delta_time;
+		newNormal = normalize(newNormal);
+		if (dot(target, newNormal) > 0.5) // clamp the offset
+		{
+			normal = newNormal;
+			velocity = newVelocity;
+		}
 
 		// Drag:
 		velocity *= 0.98f;