Add 3D physics interpolation demo

Demonstrate first person shooter and third person shooter cameras.

Author: lawnjelly

3d/physics_interpolation/.editorconfig

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+root = true
+
+[*]
+charset = utf-8

3d/physics_interpolation/README.md

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+# Physics Interpolation
+
+This demo showcases [physics interpolation](https://docs.godotengine.org/en/stable/tutorials/physics/interpolation/index.html)
+in 3D with varying camera modes (first person, third person, fixed perspective).
+This is also known as *fixed timestep interpolation*.
+
+Physics interpolation makes motion appear smooth regardless of the rendered
+framerate and physics ticks per second configured in the Project Settings.
+There are some caveats related to its usage though, such as increased latency
+and potential issues with teleporting objects. It's recommended to go
+through the
+[documentation](https://docs.godotengine.org/en/stable/tutorials/physics/interpolation/physics_interpolation_introduction.html)
+when enabling physics interpolation in a project.
+
+Physics interpolation is enabled by default in this project. Press <kbd>T</kbd>
+to toggle it while the demo is running. This allows you to see the impact on
+smoothness of physics interpolation.
+
+Language: GDScript
+
+Renderer: Compatibility
+
+## Screenshots
+
+![Screenshot](screenshots/physics_interpolation.webp)

3d/physics_interpolation/box.tscn

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+[gd_scene load_steps=4 format=3 uid="uid://cvgxw8nq67xxm"]
+
+[sub_resource type="BoxShape3D" id="BoxShape3D_pq8q7"]
+
+[sub_resource type="BoxMesh" id="BoxMesh_pyidc"]
+
+[sub_resource type="StandardMaterial3D" id="StandardMaterial3D_oq5cr"]
+albedo_color = Color(0.5544661, 0.39379695, 0.15444939, 1)
+
+[node name="Box" type="RigidBody3D"]
+mass = 10.0
+
+[node name="CollisionShape3D" type="CollisionShape3D" parent="."]
+shape = SubResource("BoxShape3D_pq8q7")
+
+[node name="MeshInstance3D" type="MeshInstance3D" parent="."]
+mesh = SubResource("BoxMesh_pyidc")
+surface_material_override/0 = SubResource("StandardMaterial3D_oq5cr")

3d/physics_interpolation/bullet.gd

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+extends RigidBody3D
+
+const APPEARANCE_LIFE = 1.0
+const MAX_LIFE = 100.0
+
+var _life := 0.0
+var _enabled := false
+
+
+func _ready() -> void:
+	$CollisionShape3D.disabled = true
+
+
+func _physics_process(_delta: float) -> void:
+	if not _enabled:
+		$CollisionShape3D.disabled = false
+		_enabled = true
+
+
+	_life += 1
+
+	var life_left := MAX_LIFE - _life
+
+	var appearance_fract := minf(float (_life) / float (APPEARANCE_LIFE), 1.0)
+	var fract := float(life_left) / float(MAX_LIFE)
+	fract *= appearance_fract
+
+	fract = maxf(fract, 0.0001)
+
+	$Scaler.scale = Vector3.ONE * fract
+
+	if _life >= MAX_LIFE:
+		queue_free()

3d/physics_interpolation/bullet.gd.uid

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+uid://dohdjr8ilotkr

3d/physics_interpolation/bullet.tscn

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+[gd_scene load_steps=14 format=3 uid="uid://2r5wc1n0ybju"]
+
+[ext_resource type="Script" uid="uid://dohdjr8ilotkr" path="res://bullet.gd" id="1_v7oki"]
+[ext_resource type="Texture2D" uid="uid://b70s43gn8c3kx" path="res://spark_particle.png" id="2_v8qja"]
+
+[sub_resource type="PhysicsMaterial" id="PhysicsMaterial_v8qja"]
+bounce = 0.61
+
+[sub_resource type="SphereShape3D" id="SphereShape3D_rtl8c"]
+radius = 0.2
+
+[sub_resource type="Gradient" id="Gradient_v8qja"]
+colors = PackedColorArray(1, 1, 1, 1, 1, 1, 1, 0)
+
+[sub_resource type="GradientTexture1D" id="GradientTexture1D_t4vbm"]
+gradient = SubResource("Gradient_v8qja")
+
+[sub_resource type="Curve" id="Curve_v8qja"]
+_data = [Vector2(0, 1), 0.0, 0.0, 0, 0, Vector2(1, 0), 0.0, 0.0, 0, 0]
+point_count = 2
+
+[sub_resource type="CurveTexture" id="CurveTexture_t4vbm"]
+curve = SubResource("Curve_v8qja")
+
+[sub_resource type="ParticleProcessMaterial" id="ParticleProcessMaterial_v7oki"]
+direction = Vector3(0, 1, 0)
+initial_velocity_max = 1.0
+gravity = Vector3(0, 1, 0)
+scale_min = 0.19999999
+scale_curve = SubResource("CurveTexture_t4vbm")
+color_ramp = SubResource("GradientTexture1D_t4vbm")
+
+[sub_resource type="StandardMaterial3D" id="StandardMaterial3D_t4vbm"]
+transparency = 1
+blend_mode = 1
+shading_mode = 0
+vertex_color_use_as_albedo = true
+albedo_color = Color(2.3357503, 3.2944162, 3.2944162, 1)
+albedo_texture = ExtResource("2_v8qja")
+texture_filter = 5
+
+[sub_resource type="QuadMesh" id="QuadMesh_rtl8c"]
+material = SubResource("StandardMaterial3D_t4vbm")
+size = Vector2(0.2, 0.2)
+
+[sub_resource type="SphereMesh" id="SphereMesh_v7oki"]
+radial_segments = 24
+rings = 12
+
+[sub_resource type="StandardMaterial3D" id="StandardMaterial3D_v7oki"]
+albedo_color = Color(0.43164876, 0.5731902, 0.5013925, 1)
+metallic = 1.0
+
+[node name="Bullet" type="RigidBody3D"]
+collision_layer = 2
+physics_material_override = SubResource("PhysicsMaterial_v8qja")
+script = ExtResource("1_v7oki")
+
+[node name="CollisionShape3D" type="CollisionShape3D" parent="."]
+shape = SubResource("SphereShape3D_rtl8c")
+
+[node name="GPUParticles3D" type="GPUParticles3D" parent="."]
+amount = 64
+transform_align = 1
+process_material = SubResource("ParticleProcessMaterial_v7oki")
+draw_pass_1 = SubResource("QuadMesh_rtl8c")
+
+[node name="Scaler" type="Node3D" parent="."]
+transform = Transform3D(0.001, 0, 0, 0, 0.001, 0, 0, 0, 0.001, 0, 0, 0)
+
+[node name="MeshInstance3D" type="MeshInstance3D" parent="Scaler"]
+transform = Transform3D(0.4, 0, 0, 0, 0.4, 0, 0, 0, 0.4, 0, 0, 0)
+mesh = SubResource("SphereMesh_v7oki")
+skeleton = NodePath("../..")
+surface_material_override/0 = SubResource("StandardMaterial3D_v7oki")

3d/physics_interpolation/icon.png.import

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+[remap]
+
+importer="texture"
+type="CompressedTexture2D"
+uid="uid://c5avn6uhdr88"
+path.s3tc="res://.godot/imported/icon.png-487276ed1e3a0c39cad0279d744ee560.s3tc.ctex"
+metadata={
+"imported_formats": ["s3tc_bptc"],
+"vram_texture": true
+}
+
+[deps]
+
+source_file="res://icon.png"
+dest_files=["res://.godot/imported/icon.png-487276ed1e3a0c39cad0279d744ee560.s3tc.ctex"]
+
+[params]
+
+compress/mode=2
+compress/high_quality=false
+compress/lossy_quality=0.7
+compress/uastc_level=0
+compress/rdo_quality_loss=0.0
+compress/hdr_compression=1
+compress/normal_map=0
+compress/channel_pack=0
+mipmaps/generate=true
+mipmaps/limit=-1
+roughness/mode=0
+roughness/src_normal=""
+process/channel_remap/red=0
+process/channel_remap/green=1
+process/channel_remap/blue=2
+process/channel_remap/alpha=3
+process/fix_alpha_border=true
+process/premult_alpha=false
+process/normal_map_invert_y=false
+process/hdr_as_srgb=false
+process/hdr_clamp_exposure=false
+process/size_limit=0
+detect_3d/compress_to=0

3d/physics_interpolation/icon.svg

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+[remap]
+
+importer="texture"
+type="CompressedTexture2D"
+uid="uid://cb05v27t8vx5t"
+path="res://.godot/imported/icon.svg-218a8f2b3041327d8a5756f3a245f83b.ctex"
+metadata={
+"vram_texture": false
+}
+
+[deps]
+
+source_file="res://icon.svg"
+dest_files=["res://.godot/imported/icon.svg-218a8f2b3041327d8a5756f3a245f83b.ctex"]
+
+[params]
+
+compress/mode=0
+compress/high_quality=false
+compress/lossy_quality=0.7
+compress/uastc_level=0
+compress/rdo_quality_loss=0.0
+compress/hdr_compression=1
+compress/normal_map=0
+compress/channel_pack=0
+mipmaps/generate=false
+mipmaps/limit=-1
+roughness/mode=0
+roughness/src_normal=""
+process/channel_remap/red=0
+process/channel_remap/green=1
+process/channel_remap/blue=2
+process/channel_remap/alpha=3
+process/fix_alpha_border=true
+process/premult_alpha=false
+process/normal_map_invert_y=false
+process/hdr_as_srgb=false
+process/hdr_clamp_exposure=false
+process/size_limit=0
+detect_3d/compress_to=0
+svg/scale=1.0
+editor/scale_with_editor_scale=false
+editor/convert_colors_with_editor_theme=false

3d/physics_interpolation/icon.svg.import

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+extends CharacterBody3D
+
+const MOUSE_SENSITIVITY = 2.5
+const CAMERA_SMOOTH_SPEED = 10.0
+const MOVE_SPEED = 3.0
+const FRICTION = 10.0
+const JUMP_VELOCITY = 8.0
+const BULLET_SPEED = 9.0
+
+var _yaw := 0.0
+var _pitch := 0.0
+var _dir := Vector3(sin(_yaw), 0, cos(_yaw))
+var _prox := 3
+
+var _tps_look_from := Vector3()
+
+enum CameraType {
+	CAM_FIXED,
+	CAM_FPS,
+	CAM_TPS,
+}
+
+var _bullet_scene: PackedScene = load("res://bullet.tscn")
+var _cam_type := CameraType.CAM_FIXED
+
+var gravity: float = ProjectSettings.get_setting("physics/3d/default_gravity")
+
+
+func _ready() -> void:
+	Input.mouse_mode = Input.MOUSE_MODE_CAPTURED
+	$Rig/Camera_TPS.top_level = true
+	cycle_camera_type()
+
+
+func _input(event: InputEvent) -> void:
+	if event is InputEventMouseMotion:
+		_yaw -= event.screen_relative.x * MOUSE_SENSITIVITY * 0.001
+		_pitch += event.screen_relative.y * MOUSE_SENSITIVITY * 0.002
+		_pitch = clamp(_pitch, -PI, PI)
+		$Rig.rotation = Vector3(0, _yaw, 0)
+
+
+func _update_camera(delta: float) -> void:
+		_dir.x = sin(_yaw)
+		_dir.z = cos(_yaw)
+
+		$Rig/Head.rotation = Vector3(_pitch * -0.5, 0, 0)
+
+		match _cam_type:
+			CameraType.CAM_TPS:
+				var target: Vector3 = $Rig/Head.get_global_transform_interpolated().origin
+				var pos := target
+				pos.x += _dir.x * _prox
+				pos.z += _dir.z * _prox
+				pos.y += 2.0 + (_pitch * (0.2 * _prox))
+
+				var offset: Vector3 = pos - _tps_look_from
+				var l: float = offset.length()
+
+				var tps_cam_speed: float = CAMERA_SMOOTH_SPEED * delta
+				if (l > tps_cam_speed):
+					offset *= tps_cam_speed / l
+				_tps_look_from += offset
+
+				$Rig/Camera_TPS.look_at_from_position(_tps_look_from, target, Vector3(0, 1, 0))
+
+
+func cycle_camera_type() -> void:
+	match _cam_type:
+		CameraType.CAM_FIXED:
+			_cam_type = CameraType.CAM_FPS
+			$Rig/Head/Camera_FPS.make_current()
+		CameraType.CAM_FPS:
+			_cam_type = CameraType.CAM_TPS
+			$Rig/Camera_TPS.make_current()
+		CameraType.CAM_TPS:
+			_cam_type = CameraType.CAM_FIXED
+			get_node("../Camera_Fixed").make_current()
+
+	# Hide body in FPS view (but keep shadow casting to improve spatial awareness).
+	if _cam_type == CameraType.CAM_FPS:
+		$Rig/Mesh_Body.cast_shadow = GeometryInstance3D.SHADOW_CASTING_SETTING_SHADOWS_ONLY
+	else:
+		$Rig/Mesh_Body.cast_shadow = GeometryInstance3D.SHADOW_CASTING_SETTING_ON
+
+
+func _process(delta: float) -> void:
+	if Input.is_action_just_pressed(&"cycle_camera_type"):
+		cycle_camera_type()
+
+	if Input.is_action_just_pressed(&"toggle_physics_interpolation"):
+		get_tree().physics_interpolation = not get_tree().physics_interpolation
+
+	if Input.is_action_just_pressed(&"fire"):
+		var bullet: RigidBody3D = _bullet_scene.instantiate()
+		var transform_3d: Transform3D = $Rig/Head/Fire_Origin.get_global_transform_interpolated()
+		bullet.position = transform_3d.origin
+		var bul_dir: Vector3 = transform_3d.basis[2].normalized()
+		bullet.linear_velocity = bul_dir * -BULLET_SPEED
+		get_parent().add_child(bullet)
+		bullet.reset_physics_interpolation()
+
+		bullet.position -= bul_dir * (1.0 - Engine.get_physics_interpolation_fraction())
+
+
+	# If we pressed reset, or too far from the origin... move back to origin.
+	if Input.is_action_just_pressed(&"reset_position") or position.length() > 10.0:
+		position = Vector3(0, 1, 0)
+		velocity = Vector3()
+		reset_physics_interpolation()
+		_yaw = 0.0
+		_pitch = 0.0
+		$Rig.rotation = Vector3(0, _yaw, 0)
+
+	if Input.is_action_just_pressed(&"jump") and is_on_floor():
+		velocity.y += JUMP_VELOCITY
+
+	_update_camera(delta)
+
+
+func _physics_process(delta: float) -> void:
+	var move := Vector3()
+
+	var input: Vector2 = Input.get_vector(&"move_left", &"move_right", &"move_forward", &"move_backward") * MOVE_SPEED
+	move.x = input.x
+	move.z = input.y
+
+	# Apply gravity.
+	move.y -= gravity * delta
+
+	# Apply mouse rotation to the move.
+	move = move.rotated(Vector3(0, 1, 0), _yaw)
+
+	velocity += move
+
+	move_and_slide()
+
+	# Apply friction to horizontal motion in a tick rate-independent manner.
+	var friction_delta := exp(-FRICTION * delta)
+	velocity = Vector3(velocity.x * friction_delta, velocity.y, velocity.z * friction_delta)