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.
+
+Controls:
+
+- <kbd>W/A/S/D</kbd>, <kbd>Arrow Keys</kbd>, <kbd>Gamepad Left Stick</kbd>, <kbd>Gamepad D-Pad</kbd>: Move
+- <kbd>Space</kbd>, <kbd>Right Mouse Button</kbd>, <kbd>Gamepad A/Cross</kbd>: Jump
+- <kbd>Left mouse button</kbd>, <kbd>Gamepad Right Trigger</kbd>: Fire
+- <kbd>Tab</kbd>, <kbd>Gamepad Select</kbd>: Change camera (first-person, third-person, fixed)
+- <kbd>R</kbd>, <kbd>Gamepad Y/Triangle</kbd>: Reset position
+- <kbd>T</kbd>, <kbd>Gamepad Left Shoulder</kbd>: Toggle 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
+
+@export var scale_curve: Curve
+
+var _enabled := false
+
+
+func _ready() -> void:
+	$CollisionShape3D.disabled = true
+
+
+func _physics_process(_delta: float) -> void:
+	# Start with physics collision disabled until the first tick.
+	# This prevents bullets from colliding with the player when first shot, while still
+	# allowing them to be moved by the player when they're laying on the ground.
+	if not _enabled:
+		$CollisionShape3D.disabled = false
+		_enabled = true
+
+	# Apply the appearance scaling according to the scale curve.
+	var time_left_ratio: float = 1.0 - $Timer.time_left / $Timer.wait_time
+	var scale_sampled := scale_curve.sample_baked(time_left_ratio)
+	$Scaler.scale = Vector3.ONE * scale_sampled
+
+
+func _on_timer_timeout() -> void:
+	queue_free()

3d/physics_interpolation/bullet.gd.uid

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3d/physics_interpolation/bullet.tscn

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+[gd_scene load_steps=15 format=3 uid="uid://2r5wc1n0ybju"]
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+[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="Curve" id="Curve_t4vbm"]
+_data = [Vector2(0, 0), 0.0, 0.0, 0, 0, Vector2(0.02, 1), 0.0, 0.0, 0, 0, Vector2(1, 0), 0.0, 0.0, 0, 0]
+point_count = 3
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+[sub_resource type="SphereShape3D" id="SphereShape3D_rtl8c"]
+radius = 0.2
+
+[sub_resource type="Gradient" id="Gradient_v8qja"]
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+
+[sub_resource type="GradientTexture1D" id="GradientTexture1D_t4vbm"]
+gradient = SubResource("Gradient_v8qja")
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+[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 = 0.2
+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(2.33575, 3.29442, 3.29442, 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(0.431649, 0.57319, 0.501392, 1)
+metallic = 1.0
+
+[node name="Bullet" type="RigidBody3D"]
+collision_layer = 2
+physics_material_override = SubResource("PhysicsMaterial_v8qja")
+script = ExtResource("1_v7oki")
+scale_curve = SubResource("Curve_t4vbm")
+
+[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")
+
+[node name="Timer" type="Timer" parent="."]
+wait_time = 5.0
+autostart = true
+
+[connection signal="timeout" from="Timer" to="." method="_on_timer_timeout"]

3d/physics_interpolation/icon.png.import

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3d/physics_interpolation/icon.svg

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