Add common use case scenarios in Multiple resolutions

This is a very common question on community platforms, so adding
some example use cases should hopefully help people.

tutorials/rendering/multiple_resolutions.rst

@@ -263,6 +263,117 @@ To configure stretching at runtime from a script, use the
 ``get_tree().set_screen_stretch()`` method (see
 :ref:`SceneTree.set_screen_stretch() <class_SceneTree_method_set_screen_stretch>`).
 
+Common use case scenarios
+-------------------------
+
+The following settings are recommended to support multiple resolutions and aspect
+ratios well.
+
+Desktop game
+^^^^^^^^^^^^
+
+**Non-pixel art:**
+
+- Set the base window width to ``1920`` and window height to ``1080``. If you have a
+  display smaller than 1920×1080, set **Test Width** and **Test Height** to
+  lower values to make the window smaller when the project starts.
+- Alternatively, if you're targeting high-end devices primarily, set the base
+  window width to ``3840`` and window height to ``2160``.
+  This allows you to provide higher resolution 2D assets, resulting in crisper
+  visuals at the cost of higher memory usage and file sizes.
+  Note that this will make non-mipmapped textures grainy on low resolution devices,
+  so make sure to follow the instructions described in
+  :ref:`doc_multiple_resolutions_reducing_aliasing_on_downsampling`.
+- Set the stretch mode to ``2d``.
+- Set the stretch aspect to ``expand``. This allows for supporting multiple aspect ratios
+  and makes better use of tall smartphone displays (such as 18:9 or 19:9 aspect ratios).
+- Configure Control nodes' anchors to snap to the correct corners using the **Layout** menu.
+
+**Pixel art:**
+
+- Set the base window size to the viewport size you intend to use. Most pixel art games
+  use viewport sizes between 256×224 and 640×480. Higher viewport sizes will
+  require using higher resolution artwork, unless you intend to show more of the
+  game world at a given time.
+- Set the stretch mode to ``viewport``.
+- Set the stretch aspect to ``keep`` to enforce a single aspect ratio (with
+  black bars). As an alternative, you can set the stretch aspect to ``expand`` to
+  support multiple aspect ratios.
+- If using the ``expand`` stretch aspect, Configure Control nodes' anchors to
+  snap to the correct corners using the **Layout** menu.
+
+.. note::
+
+    The ``viewport`` stretch mode provides low-resolution rendering that is then
+    stretched to the final window size. If you are OK with sprites being able to
+    move or rotate in "sub-pixel" positions or wish to have a high resolution 3D
+    viewport, you should use the ``2d`` stretch mode instead of the ``viewport``
+    stretch mode.
+
+    Godot currently doesn't have a way to enforce integer scaling when using the
+    ``2d`` or ``viewport`` stretch mode, which means pixel art may look bad if the
+    final window size is not a multiple of the base window size.
+    To fix this, use an add-on such as the `Integer Resolution Handler <https://github.com/Yukitty/godot-addon-integer_resolution_handler>`__.
+
+Mobile game in landscape mode
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Godot is configured to use landscape mode by default. This means you don't need
+to change the display orientation project setting.
+
+- Set the base window width to ``1280`` and window height to ``720``.
+- Alternatively, if you're targeting high-end devices primarily, set the base
+  window width to ``1920`` and window height to ``1080``.
+  This allows you to provide higher resolution 2D assets, resulting in crisper
+  visuals at the cost of higher memory usage and file sizes. Many devices have
+  even higher resolution displays (1440p), but the difference with 1080p is
+  barely visible given the small size of smartphone displays.
+  Note that this will make non-mipmapped textures grainy on low resolution devices,
+  so make sure to follow the instructions described in
+  :ref:`doc_multiple_resolutions_reducing_aliasing_on_downsampling`.
+- Set the stretch mode to ``2d``.
+- Set the stretch aspect to ``expand``. This allows for supporting multiple aspect ratios
+  and makes better use of tall smartphone displays (such as 18:9 or 19:9 aspect ratios).
+- Configure Control nodes' anchors to snap to the correct corners using the **Layout** menu.
+
+Mobile game in portrait mode
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+- Set the base window width to ``720`` and window height to ``1080``.
+- Alternatively, if you're targeting high-end devices primarily, set the base
+  window width to ``1080`` and window height to ``1920``.
+  This allows you to provide higher resolution 2D assets, resulting in crisper
+  visuals at the cost of higher memory usage and file sizes. Many devices have
+  even higher resolution displays (1440p), but the difference with 1080p is
+  barely visible given the small size of smartphone displays.
+  Note that this will make non-mipmapped textures grainy on low resolution devices,
+  so make sure to follow the instructions described in
+  :ref:`doc_multiple_resolutions_reducing_aliasing_on_downsampling`.
+- Set **Display > Window > Handheld > Orientation** to ``portrait``.
+- Set the stretch mode to ``2d``.
+- Set the stretch aspect to ``expand``. This allows for supporting multiple aspect ratios
+  and makes better use of tall smartphone displays (such as 18:9 or 19:9 aspect ratios).
+- Configure Control nodes' anchors to snap to the correct corners using the **Layout** menu.
+
+Non-game application
+^^^^^^^^^^^^^^^^^^^^
+
+- Set the base window width and height to the smallest window size that you intend to target.
+  This is not required, but this ensures that you design your UI with small window sizes in mind.
+- Keep the stretch mode to its default value, ``disabled``.
+- Keep the stretch aspect to its default value, ``ignore``
+  (its value won't be used since the stretch mode is ``disabled``).
+- You can define a minimum window size by setting ``OS.min_window_size`` in a
+  script's ``_ready()`` function. This prevents the user from resizing the application
+  below a certain size, which could break the UI layout.
+
+.. note::
+
+    Godot doesn't support manually overriding the 2D scale factor yet, so it is
+    not possible to have hiDPI support in non-game applications. Due to this, it
+    is recommended to leave **Allow Hidpi** disabled in non-game applications to
+    allow for the OS to use its low-DPI fallback.
+
 hiDPI support
 -------------
 
@@ -285,6 +396,8 @@ other platforms.
     from the editor will only be DPI-aware if **Allow Hidpi** is enabled in the
     Project Settings.
 
+.. _doc_multiple_resolutions_reducing_aliasing_on_downsampling:
+
 Reducing aliasing on downsampling
 ---------------------------------