Improve documentation on "physics spiral of death" in ProjectSettings

- Link to Troubleshooting physics issues documentation page in various
  locations in the class reference.

Author: Calinou

doc/classes/AnimatableBody2D.xml

@@ -8,6 +8,8 @@
 		When [AnimatableBody2D] is moved, its linear and angular velocity are estimated and used to affect other physics bodies in its path. This makes it useful for moving platforms, doors, and other moving objects.
 	</description>
 	<tutorials>
+		<link title="Physics introduction">$DOCS_URL/tutorials/physics/physics_introduction.html</link>
+		<link title="Troubleshooting physics issues">$DOCS_URL/tutorials/physics/troubleshooting_physics_issues.html</link>
 	</tutorials>
 	<members>
 		<member name="sync_to_physics" type="bool" setter="set_sync_to_physics" getter="is_sync_to_physics_enabled" default="true">

doc/classes/AnimatableBody3D.xml

@@ -8,6 +8,8 @@
 		When [AnimatableBody3D] is moved, its linear and angular velocity are estimated and used to affect other physics bodies in its path. This makes it useful for moving platforms, doors, and other moving objects.
 	</description>
 	<tutorials>
+		<link title="Physics introduction">$DOCS_URL/tutorials/physics/physics_introduction.html</link>
+		<link title="Troubleshooting physics issues">$DOCS_URL/tutorials/physics/troubleshooting_physics_issues.html</link>
 		<link title="3D Physics Tests Demo">https://godotengine.org/asset-library/asset/2747</link>
 		<link title="Third Person Shooter (TPS) Demo">https://godotengine.org/asset-library/asset/2710</link>
 		<link title="3D Voxel Demo">https://godotengine.org/asset-library/asset/2755</link>

doc/classes/CharacterBody2D.xml

@@ -8,6 +8,8 @@
 		For game objects that don't require complex movement or collision detection, such as moving platforms, [AnimatableBody2D] is simpler to configure.
 	</description>
 	<tutorials>
+		<link title="Physics introduction">$DOCS_URL/tutorials/physics/physics_introduction.html</link>
+		<link title="Troubleshooting physics issues">$DOCS_URL/tutorials/physics/troubleshooting_physics_issues.html</link>
 		<link title="Kinematic character (2D)">$DOCS_URL/tutorials/physics/kinematic_character_2d.html</link>
 		<link title="Using CharacterBody2D">$DOCS_URL/tutorials/physics/using_character_body_2d.html</link>
 		<link title="2D Kinematic Character Demo">https://godotengine.org/asset-library/asset/2719</link>

doc/classes/CharacterBody3D.xml

@@ -8,6 +8,8 @@
 		For game objects that don't require complex movement or collision detection, such as moving platforms, [AnimatableBody3D] is simpler to configure.
 	</description>
 	<tutorials>
+		<link title="Physics introduction">$DOCS_URL/tutorials/physics/physics_introduction.html</link>
+		<link title="Troubleshooting physics issues">$DOCS_URL/tutorials/physics/troubleshooting_physics_issues.html</link>
 		<link title="Kinematic character (2D)">$DOCS_URL/tutorials/physics/kinematic_character_2d.html</link>
 		<link title="3D Kinematic Character Demo">https://godotengine.org/asset-library/asset/2739</link>
 		<link title="3D Platformer Demo">https://godotengine.org/asset-library/asset/2748</link>

doc/classes/PhysicsBody2D.xml

@@ -8,6 +8,7 @@
 	</description>
 	<tutorials>
 		<link title="Physics introduction">$DOCS_URL/tutorials/physics/physics_introduction.html</link>
+		<link title="Troubleshooting physics issues">$DOCS_URL/tutorials/physics/troubleshooting_physics_issues.html</link>
 	</tutorials>
 	<methods>
 		<method name="add_collision_exception_with">

doc/classes/PhysicsBody3D.xml

@@ -9,6 +9,7 @@
 	</description>
 	<tutorials>
 		<link title="Physics introduction">$DOCS_URL/tutorials/physics/physics_introduction.html</link>
+		<link title="Troubleshooting physics issues">$DOCS_URL/tutorials/physics/troubleshooting_physics_issues.html</link>
 	</tutorials>
 	<methods>
 		<method name="add_collision_exception_with">

doc/classes/ProjectSettings.xml

@@ -2328,7 +2328,8 @@
 			Enables [member Viewport.physics_object_picking] on the root viewport.
 		</member>
 		<member name="physics/common/max_physics_steps_per_frame" type="int" setter="" getter="" default="8">
-			Controls the maximum number of physics steps that can be simulated each rendered frame. The default value is tuned to avoid "spiral of death" situations where expensive physics simulations trigger more expensive simulations indefinitely. However, the game will appear to slow down if the rendering FPS is less than [code]1 / max_physics_steps_per_frame[/code] of [member physics/common/physics_ticks_per_second]. This occurs even if [code]delta[/code] is consistently used in physics calculations. To avoid this, increase [member physics/common/max_physics_steps_per_frame] if you have increased [member physics/common/physics_ticks_per_second] significantly above its default value.
+			Controls the maximum number of physics steps that can be simulated each rendered frame. The default value is tuned to avoid situations where the framerate suddenly drops to a very low value beyond a certain amount of physics simulation. This occurs because the physics engine can't keep up with the expected simulation rate. In this case, the framerate will start dropping, but the engine is only allowed to simulate a certain number of physics steps per rendered frame. This snowballs into a situation where framerate keeps dropping until it reaches a very low framerate (typically 1-2 FPS) and is called the [i]physics spiral of death[/i].
+			However, the game will appear to slow down if the rendering FPS is less than [code]1 / max_physics_steps_per_frame[/code] of [member physics/common/physics_ticks_per_second]. This occurs even if [code]delta[/code] is consistently used in physics calculations. To avoid this, increase [member physics/common/max_physics_steps_per_frame] if you have increased [member physics/common/physics_ticks_per_second] significantly above its default value.
 			[b]Note:[/b] This property is only read when the project starts. To change the maximum number of simulated physics steps per frame at runtime, set [member Engine.max_physics_steps_per_frame] instead.
 		</member>
 		<member name="physics/common/physics_interpolation" type="bool" setter="" getter="" default="false">

doc/classes/RigidBody2D.xml

@@ -11,6 +11,8 @@
 		[b]Note:[/b] Changing the 2D transform or [member linear_velocity] of a [RigidBody2D] very often may lead to some unpredictable behaviors. If you need to directly affect the body, prefer [method _integrate_forces] as it allows you to directly access the physics state.
 	</description>
 	<tutorials>
+		<link title="Physics introduction">$DOCS_URL/tutorials/physics/physics_introduction.html</link>
+		<link title="Troubleshooting physics issues">$DOCS_URL/tutorials/physics/troubleshooting_physics_issues.html</link>
 		<link title="2D Physics Platformer Demo">https://godotengine.org/asset-library/asset/2725</link>
 		<link title="Instancing Demo">https://godotengine.org/asset-library/asset/2716</link>
 	</tutorials>

doc/classes/RigidBody3D.xml

@@ -12,6 +12,7 @@
 	</description>
 	<tutorials>
 		<link title="Physics introduction">$DOCS_URL/tutorials/physics/physics_introduction.html</link>
+		<link title="Troubleshooting physics issues">$DOCS_URL/tutorials/physics/troubleshooting_physics_issues.html</link>
 		<link title="3D Truck Town Demo">https://godotengine.org/asset-library/asset/2752</link>
 		<link title="3D Physics Tests Demo">https://godotengine.org/asset-library/asset/2747</link>
 	</tutorials>

doc/classes/StaticBody2D.xml

@@ -9,6 +9,8 @@
 		[StaticBody2D] is useful for completely static objects like floors and walls, as well as moving surfaces like conveyor belts and circular revolving platforms (by using [member constant_linear_velocity] and [member constant_angular_velocity]).
 	</description>
 	<tutorials>
+		<link title="Physics introduction">$DOCS_URL/tutorials/physics/physics_introduction.html</link>
+		<link title="Troubleshooting physics issues">$DOCS_URL/tutorials/physics/troubleshooting_physics_issues.html</link>
 	</tutorials>
 	<members>
 		<member name="constant_angular_velocity" type="float" setter="set_constant_angular_velocity" getter="get_constant_angular_velocity" default="0.0">