Start documentation.

1524487e · Ilya Portnov · c502fa8a · 1524487e · 1524487e · 1524487e
--- a/docs/nodes/list_struct/levels.rst
+++ b/docs/nodes/list_struct/levels.rst
+List Levels
+===========
+
+Functionality
+-------------
+
+This node allows the user to manipulate with nesting structure of data by setting checkboxes. It allows to:
+
+* Remove a level of nesting by concatenating nested lists of some level, or
+* Add a level of nesting by adding another pair of square brackets around nested list of some level, or
+* do both things at the same or at different nesting levels.
+
+This node works with nested lists or tuples. Numpy arrays are considered to be atomic objects.
+
+Inputs
+------
+
+This node has the following input:
+
+* **Data**. Input data. This node supports data of any standard type (numbers,
+  vertices, surfaces and so on), with arbitrary nesting level. This input is
+  mandatory.
+
+Parameters
+----------
+
+When **Data** input is connected, the interface of the node presents a table.
+Each row of the table describes one nesting level of input data, and defines
+what do you want to do with data at this nesting level. The table has the
+following columns:
+
+* **Depth**. This shows the nesting depth of this level, i.e. how deeply nested
+  this data is, counting from the outermost list. Outermost list always has
+  depth of 0, one that is nested in it has depth of 1, and so on.
+* **Nesting**. This shows how many nesting levels are inside each item of data
+  at this level. At the innermost nesting level, each item of the list is an
+  "atomic object", for example it can be integer number, floating-point number,
+  surface or curve, and so on, but not a list or tuple. So, the innermost data
+  level has nesting level equal to 0 (zero). A list which consists of atomic
+  objects has nesting level of 1, and so on.
+* **Shape**. This describes the shape of data at this level. For lists or
+  tuples, it shows whether this is a list or tuple, and also the number of
+  items in it, in square brackets. For atomic objects, it shows the type of the
+  data ("float", or "int", or "SvSurface", and so on).
+* **Flatten**. This column contains a checkbox. If checked, the node will
+  concatenate all lists contained in list at this nesting level. Obviously,
+  atomic objects (nesting of 0) do not contain any nested objects, so for the
+  innermost level this checkbox is not available. For lists that contain atomic
+  objects (nesting of 1), this checkbox is not available either, as there are
+  no nested lists too. This checkbox does transform data only at one level, it
+  does not "go deeper" automatically. So, if you check this checkbox, you
+  always decrease nesting level of whole data by 1. To give some examples,
+
+   * ``[[1, 2], [3, 4]]`` is transformed into ``[1, 2, 3, 4]``.
+   * ``[[[1], [2]], [[3], [4]]]`` is transformed into ``[[1], [2], [3], [4]]``.
+
+* **Wrap**. This column contains a checkbox. If checked, the node will put the
+  data at this nesting level in a separate list, i.e. wrap it in additional
+  pair of square brackets. So, by checking this checkbox, you always increase
+  the nesting level of whole data by 1. For example, if you check this
+  parameter at the innermost level (nesting of 0), the node will create a
+  separate list for each atomic object (wrap each atomic object into a list). 
+
+For simple shapes of data, many combinations of checkboxes will give identical
+results; but for more deeply nested data, or when having more items at
+outermost levels, there will be more different options. You can also connect
+several "List Levels" nodes to do even more complex manipulations with data
+structure.
+
--- a/docs/nodes/list_struct/list_struct_index.rst
+++ b/docs/nodes/list_struct/list_struct_index.rst
@@ -17,3 +17,5 @@ List Struct
   sort
   split
   start_end
+   levels
+
--- a/nodes/list_struct/levels.py
+++ b/nodes/list_struct/levels.py
@@ -56,12 +56,16 @@ class SvListLevelsNode(bpy.types.Node, SverchCustomTreeNode):
    '''
    bl_idname = 'SvListLevelsNode'
    bl_label = 'List Levels'
-    bl_icon = 'OUTLINER_OB_EMPTY'
+    bl_icon = 'OUTLINER'

    levels_config : CollectionProperty(type=SvNestingLevelEntry)
    prev_nesting_level : IntProperty(default = 0, options = {'SKIP_SAVE'})

    def draw_buttons(self, context, layout):
+        n = len(self.levels_config)
+        if not n:
+            layout.label(text="No data passed")
+            return
        grid = layout.grid_flow(row_major=True, columns=5, align=True)

        grid.label(text='Depth')
@@ -70,7 +74,6 @@ class SvListLevelsNode(bpy.types.Node, SverchCustomTreeNode):
        grid.label(text='Flatten')
        grid.label(text='Wrap')

-        n = len(self.levels_config)
        for i, entry in enumerate(self.levels_config):
            nesting = n-i-1
            level_str = str(i)