Document converting CSG nodes to MeshInstance3D and related lightmapping workflow (#10229)

* Document converting CSG nodes to MeshInstance3D and related lightmapping workflow

---------

Co-authored-by: Max Hilbrunner <mhilbrunner@users.noreply.github.com>
Co-authored-by: tetrapod <145553014+tetrapod00@users.noreply.github.com>

tutorials/3d/csg_tools.rst

@@ -296,8 +296,39 @@ in the **Scale** property will cause the texture to repeat more often.
          the material onto, click the dropdown arrow next to its material
          property then choose **Paste**.
 
+.. _doc_csg_tools_converting_to_mesh_instance_3d:
+
+Converting to MeshInstance3D
+----------------------------
+
+Since Godot 4.4, you can convert a CSG node and its children to a :ref:`class_MeshInstance3D` node.
+
+This has several benefits:
+
+- Bake lightmaps, since UV2 can be generated on a MeshInstance3D.
+- Bake occlusion culling, since the occlusion culling bake process only takes MeshInstance3D into account.
+- Faster loading times, since the CSG mesh no longer needs to be rebuilt when the scene loads.
+- Better performance when updating the node's transform if using the mesh within another CSG node.
+
+To convert a CSG node to a MeshInstance3D node, select it, then choose
+**CSG > Bake Mesh Instance** in the toolbar. The MeshInstance3D node
+will be created as a sibling. Note that the CSG node that was used for baking is **not** hidden
+automatically, so remember to hide it to prevent its geometry from overlapping with the newly created
+MeshInstance3D.
+
+You can also create a trimesh collision shape using **CSG > Bake Collision Shape**.
+The generated :ref:`class_CollisionShape3D` node must be a child of a :ref:`class_StaticBody3D`
+or :ref:`class_AnimatableBody3D` node to be effective.
+
+.. tip::
+
+    Remember to keep the original CSG node in the scene tree, so that you can
+    perform changes to the geometry later if needed. To make changes to the
+    geometry, remove the MeshInstance3D node and make the root CSG node visible
+    again.
+
 Exporting as glTF
-------------------------
+-----------------
 
 It can be useful to block out a level using CSG, then export it as a 3d model, to
 import into 3D modeling software. You can do this by selecting **Scene > Export As... >

tutorials/3d/global_illumination/using_lightmap_gi.rst

@@ -202,6 +202,25 @@ lightmap texture, which varies depending on the mesh's size properties and the
 **UV2 Padding** value. **Lightmap Size Hint** should not be manually changed, as
 any modifications will be lost when the scene is reloaded.
 
+Generating UV2 for CSG nodes
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Since Godot 4.4, you can
+:ref:`convert a CSG node and its children to a MeshInstance3D <doc_csg_tools_converting_to_mesh_instance_3d>`.
+This can be used to bake lightmaps on a CSG node by following these steps:
+
+- Select the root CSG node and choose **CSG > Bake Mesh Instance** at the top of the 3D editor viewport.
+- Hide the root CSG node that was just baked (it is not hidden automatically).
+- Select the newly created MeshInstance3D node and choose **Mesh > Unwrap UV2 for Lightmap/AO**.
+- Bake lightmaps.
+
+.. tip::
+
+    Remember to keep the original CSG node in the scene tree, so that you can
+    perform changes to the geometry later if needed. To make changes to the
+    geometry, remove the MeshInstance3D node and make the root CSG node visible
+    again.
+
 Checking UV2
 ^^^^^^^^^^^^
 

tutorials/3d/occlusion_culling.rst

@@ -79,7 +79,8 @@ How occlusion culling works in Godot
 
 .. note::
 
-    *"occluder" refers to the shape blocking the view, while "occludee" refers to the object being hidden.*
+    "occluder" refers to the shape blocking the view, while "occludee" refers to
+    the object being hidden.
 
 In Godot, occlusion culling works by rasterizing the scene's occluder geometry
 to a low-resolution buffer on the CPU. This is done using
@@ -124,6 +125,10 @@ Automatically baking occluders (recommended)
     those to be treated as occluders, you have to manually create occluder
     shapes that (roughly) match their geometry.
 
+    Since Godot 4.4, CSG nodes can be taken into account in the baking process if they are
+    :ref:`converted to a MeshInstance3D <doc_csg_tools_converting_to_mesh_instance_3d>`
+    before baking occluders.
+
     This restriction does not apply to *occludees*. Any node type that inherits
     from GeometryInstance3D can be occluded.