classref: Sync with current master branch (0c51ede)

classes/class_mainloop.rst

@@ -262,11 +262,13 @@ Called once during initialization.
 
 :ref:`bool<class_bool>` **_physics_process**\ (\ delta\: :ref:`float<class_float>`\ ) |virtual| :ref:`🔗<class_MainLoop_private_method__physics_process>`
 
-Called each physics frame with the time since the last physics frame as argument (``delta``, in seconds). Equivalent to :ref:`Node._physics_process()<class_Node_private_method__physics_process>`.
+Called each physics tick. ``delta`` is the logical time between physics ticks in seconds and is equal to :ref:`Engine.time_scale<class_Engine_property_time_scale>` / :ref:`Engine.physics_ticks_per_second<class_Engine_property_physics_ticks_per_second>`. Equivalent to :ref:`Node._physics_process()<class_Node_private_method__physics_process>`.
 
-If implemented, the method must return a boolean value. ``true`` ends the main loop, while ``false`` lets it proceed to the next frame.
+If implemented, the method must return a boolean value. ``true`` ends the main loop, while ``false`` lets it proceed to the next step.
 
-\ **Note:** ``delta`` will be larger than expected if running at a framerate lower than :ref:`Engine.physics_ticks_per_second<class_Engine_property_physics_ticks_per_second>` / :ref:`Engine.max_physics_steps_per_frame<class_Engine_property_max_physics_steps_per_frame>` FPS. This is done to avoid "spiral of death" scenarios where performance would plummet due to an ever-increasing number of physics steps per frame. This behavior affects both :ref:`_process()<class_MainLoop_private_method__process>` and :ref:`_physics_process()<class_MainLoop_private_method__physics_process>`. As a result, avoid using ``delta`` for time measurements in real-world seconds. Use the :ref:`Time<class_Time>` singleton's methods for this purpose instead, such as :ref:`Time.get_ticks_usec()<class_Time_method_get_ticks_usec>`.
+\ **Note:** :ref:`_physics_process()<class_MainLoop_private_method__physics_process>` may be called up to :ref:`Engine.max_physics_steps_per_frame<class_Engine_property_max_physics_steps_per_frame>` times per (idle) frame. This step limit may be reached when the engine is suffering performance issues.
+
+\ **Note:** Accumulated ``delta`` may diverge from real world seconds.
 
 .. rst-class:: classref-item-separator
 
@@ -278,11 +280,15 @@ If implemented, the method must return a boolean value. ``true`` ends the main l
 
 :ref:`bool<class_bool>` **_process**\ (\ delta\: :ref:`float<class_float>`\ ) |virtual| :ref:`🔗<class_MainLoop_private_method__process>`
 
-Called each process (idle) frame with the time since the last process frame as argument (in seconds). Equivalent to :ref:`Node._process()<class_Node_private_method__process>`.
+Called on each idle frame, prior to rendering, and after physics ticks have been processed. ``delta`` is the time between frames in seconds. Equivalent to :ref:`Node._process()<class_Node_private_method__process>`.
 
 If implemented, the method must return a boolean value. ``true`` ends the main loop, while ``false`` lets it proceed to the next frame.
 
-\ **Note:** ``delta`` will be larger than expected if running at a framerate lower than :ref:`Engine.physics_ticks_per_second<class_Engine_property_physics_ticks_per_second>` / :ref:`Engine.max_physics_steps_per_frame<class_Engine_property_max_physics_steps_per_frame>` FPS. This is done to avoid "spiral of death" scenarios where performance would plummet due to an ever-increasing number of physics steps per frame. This behavior affects both :ref:`_process()<class_MainLoop_private_method__process>` and :ref:`_physics_process()<class_MainLoop_private_method__physics_process>`. As a result, avoid using ``delta`` for time measurements in real-world seconds. Use the :ref:`Time<class_Time>` singleton's methods for this purpose instead, such as :ref:`Time.get_ticks_usec()<class_Time_method_get_ticks_usec>`.
+\ **Note:** When the engine is struggling and the frame rate is lowered, ``delta`` will increase. When ``delta`` is increased, it's capped at a maximum of :ref:`Engine.time_scale<class_Engine_property_time_scale>` \* :ref:`Engine.max_physics_steps_per_frame<class_Engine_property_max_physics_steps_per_frame>` / :ref:`Engine.physics_ticks_per_second<class_Engine_property_physics_ticks_per_second>`. As a result, accumulated ``delta`` may not represent real world time.
+
+\ **Note:** When ``--fixed-fps`` is enabled or the engine is running in Movie Maker mode (see :ref:`MovieWriter<class_MovieWriter>`), process ``delta`` will always be the same for every frame, regardless of how much time the frame took to render.
+
+\ **Note:** Frame delta may be post-processed by :ref:`OS.delta_smoothing<class_OS_property_delta_smoothing>` if this is enabled for the project.
 
 .. |virtual| replace:: :abbr:`virtual (This method should typically be overridden by the user to have any effect.)`
 .. |required| replace:: :abbr:`required (This method is required to be overridden when extending its base class.)`