[Bf-docboard-svn] bf-manual: [7785] trunk/blender_docs/manual/modeling/geometry_nodes/attributes_reference.rst: Improve the attribute reference page

[Hans Goudey]

Revision: 7785
          https://developer.blender.org/rBM7785
Author:   HooglyBoogly
Date:     2021-02-24 04:46:08 +0100 (Wed, 24 Feb 2021)
Log Message:
-----------
Improve the attribute reference page

Rephrase for simplicity, add more information.

Modified Paths:
--------------
    trunk/blender_docs/manual/modeling/geometry_nodes/attributes_reference.rst

Modified: trunk/blender_docs/manual/modeling/geometry_nodes/attributes_reference.rst
===================================================================
--- trunk/blender_docs/manual/modeling/geometry_nodes/attributes_reference.rst	2021-02-22 23:40:40 UTC (rev 7784)
+++ trunk/blender_docs/manual/modeling/geometry_nodes/attributes_reference.rst	2021-02-24 03:46:08 UTC (rev 7785)
@@ -11,7 +11,7 @@
 
 .. note::
 
-   The blue attribute sockets are just string sockets, used to look up the list of data stored in the geometry.
+   The blue attribute sockets are just string sockets, used to find which attribute in the geometry to use.
 
 .. note::
 
@@ -21,6 +21,8 @@
 Built-In Attributes
 ===================
 
+Built-in attributes always exist, and cannot be removed. Their data type can not be changed.
+
 .. list-table::
    :widths: 10 10 50
    :header-rows: 1
@@ -38,9 +40,9 @@
 
    * - **radius**
      - *Float*
-     - Used to set the size for the points created by the
+     - A built-in atribute on point cloud data created by the
        :doc:`Point Distribute Node </modeling/geometry_nodes/point/point_distribute>`
-       in the viewport.
+       Used to set the size for the points in the viewport.
 
    * - **material_index**
      - *Integer*
@@ -50,6 +52,14 @@
 Naming Conventions
 ==================
 
+These attributes do not exist by default, but are used implicitly by certain nodes. The data type of these
+attributes can be changed, just like any attribute besides the built-in attributes.
+
+If the attributes don't exist yet, a default value is used, which can depend on the situation.
+For example, in the :doc:`Point Instance Node </modeling/geometry_nodes/point/point_instance>`,
+the default value for `scale` is a unit scale of (1, 1, 1), but the default value for new attributes
+in the "Attribute" nodes is zero.
+
 .. list-table::
    :widths: 10 10 50
    :header-rows: 1
@@ -60,16 +70,16 @@
 
    * - **rotation**
      - *Vector*
-     - Used in the :doc:`Point Distribute Node </modeling/geometry_nodes/point/point_distribute>` to
-       control the rotation of instanced objects or collections. This is adjusted by
+     - Used in the :doc:`Point Instance Node </modeling/geometry_nodes/point/point_instance>` to
+       control the rotation of instances. Adjusted by
        the :doc:`Point Rotate Node </modeling/geometry_nodes/point/point_rotate>` and the
        :doc:`Align Rotation to Vector Node </modeling/geometry_nodes/point/align_rotation_to_vector>`.
 
    * - **scale**
      - *Vector*
-     - Used in the :doc:`Point Distribute Node </modeling/geometry_nodes/point/point_distribute>` to control the scale.
-       This is adjusted by the :doc:`Point Scale Node </modeling/geometry_nodes/point/point_rotate>`
-       or other attribute nodes.
+     - Used in the :doc:`Point Distribute Node </modeling/geometry_nodes/point/point_distribute>` 
+       to control the scale of instances. Adjusted by the 
+       :doc:`Point Scale Node </modeling/geometry_nodes/point/point_rotate>` or other attribute nodes.
 
    * - **id**
      - *Integer*
@@ -82,11 +92,13 @@
 Custom Attributes
 =================
 
-Vertex groups, uv maps and vertex colors are available as attributes in geometry nodes.
+Vertex groups, UV maps and vertex colors are available as attributes in geometry nodes.
 They are referred to by their name.
 Naming collisions (e.g. a vertex group and a uv map with the same name) should be avoided.
 If there is a naming collision, only one of the attributes is accessible in geometry nodes.
 
-Note, that geometry nodes does not always produce e.g. vertex groups if a node like
+Attributes with any other name can also be created by nodes, when the name is used for the first time.
+
+Note that geometry nodes does not always produce e.g. vertex groups if a node like
 :doc:`Join Geometry </modeling/geometry_nodes/geometry/join_geometry>` is used.
 That implies that other functionality in Blender that expects vertex groups, cannot access the attribute anymore.