Update intro to 3D images, document preview light

(cherry picked from commit e616c4b6c66fd72eb4c91a1623d3caed5cb8e832)

tutorials/3d/introduction_to_3d.rst

@@ -24,11 +24,7 @@ Node3D node
 Following this reasoning, the 3D engine uses the :ref:`Node3D <class_Node3D>`
 node for everything 3D.
 
-.. note:: Be aware that "Spatial" Nodes are now called "Node3D"
-   starting with Godot 4. Any Godot 3.x references to "Spatial"
-   Nodes refer to "Node3D" in Godot 4.
-
-.. image:: img/tuto_3d1.png
+.. image:: img/tuto_3d1.webp
 
 Node3Ds have a local transform, which is relative to the parent
 node (as long as the parent node is also of **or inherits from** the type
@@ -37,7 +33,7 @@ Node3D). This transform can be accessed as a 4×3
 members representing location, Euler rotation (X, Y and Z angles) and
 scale.
 
-.. image:: img/tuto_3d2.png
+.. image:: img/tuto_3d2.webp
 
 3D content
 ~~~~~~~~~~
@@ -117,14 +113,14 @@ Editing 3D scenes is done in the 3D tab. This tab can be selected
 manually, but it will be automatically enabled when a Node3D node is
 selected.
 
-.. image:: img/tuto_3d3.png
+.. image:: img/tuto_3d3.webp
 
 Default 3D scene navigation controls are similar to Blender (aiming to
 have some sort of consistency in the free software pipeline..), but
 options are included to customize mouse buttons and behavior to be
 similar to other tools in the Editor Settings:
 
-.. image:: img/tuto_3d4.png
+.. image:: img/tuto_3d4.webp
 
 Coordinate system
 -----------------
@@ -167,7 +163,7 @@ respectively. This convention applies to the grid and other gizmos too
 (and also to the shader language, ordering of components for
 Vector3, Color, etc.).
 
-.. image:: img/tuto_3d5.png
+.. image:: img/tuto_3d5.webp
 
 Some useful keybindings:
 
@@ -210,26 +206,37 @@ View menu
 
 The view options are controlled by the "View" menu in the viewport's toolbar.
 
-.. image:: img/tuto_3d6.png
+.. image:: img/tuto_3d6.webp
 
 You can hide the gizmos in the 3D view of the editor through this menu:
 
-.. image:: img/tuto_3d6_1.png
+.. image:: img/tuto_3d6_1.webp
 
 To hide a specific type of gizmos, you can toggle them off in the "View" menu.
 
-.. image:: img/tuto_3d6_2.png
+.. image:: img/tuto_3d6_2.webp
+
+preview environment and light
+-----------------------------
+
+By default, any 3D scene that doesn't have a :ref:`WorldEnvironment <class_WorldEnvironment>`
+node, or a :ref:`DirectionalLight3D <class_DirectionalLight3D>`, will have
+a preview turned on for what it's missing to light the scene.
 
-Default environment
--------------------
+The preview light and environment will only be visible in the scene while
+in the editor. If you run the scene or export the project they will not
+affect the scene.
 
-When created from the Project Manager, the 3D environment has a default sky.
+The preview light and environment can be turned on or off from the top menu
+by clicking on their respective icon, and the 3 dots dropdown menu next to
+those icons can be used to adjust the properties of the preview environment
+and light.
 
-.. image:: img/tuto_3d8.png
+.. image:: img/tuto_3d8.webp
 
-Given how physically-based rendering works, it is advised to always try to
-work with a default environment in order to provide indirect and reflected
-light to your objects.
+The same preview sun and environment is used for every scene in the same project,
+So only make adjustments that would apply to all of the scenes you will need a preview
+light and environment for.
 
 Cameras
 -------
@@ -239,7 +246,7 @@ displayed unless a :ref:`Camera3D <class_Camera3D>` is
 also added to the scene. Cameras can work in either orthogonal or
 perspective projections:
 
-.. image:: img/tuto_3d10.png
+.. image:: img/tuto_3d10.webp
 
 Cameras are associated with (and only display to) a parent or grandparent
 viewport. Since the root of the scene tree is a viewport, cameras will