************
Introduction
************

.. admonition:: Reference
   :class: refbox

   | Mode:     Object or Edit Modes
   | Menu:     :menuselection:`Add --> Meta`
   | Hotkey:   :kbd:`Shift-A`


Meta objects are *implicit surfaces*,
meaning that they are *not explicitly* defined by vertices (as meshes are)
or control points (as surfaces are): they exist *procedurally*.
Meta objects are literally mathematical formulas that are calculated on-the-fly by Blender.

A very distinct visual characteristic of metas is that they are fluid *mercurial*,
or *clay-like* forms that have a "rounded" shape. Furthermore,
when two meta objects get close to one another, they begin to interact with one another.
They "blend" or "merge", as water droplets do, especially in zero-g (which, by the way, makes
them very handy for modeling streams of water when you do not want to do a fluid simulation).
If they subsequently move away from one another, they restore their original shape.

Each of these is defined by its own underlying mathematical structure (:doc:`/modeling/metas/structure`),
and you can at any time switch between them using the *Active Element* panel.

Typically *Meta* objects are used for special effects or as a basis for modeling.
For example, you could use a collection of metas to form the initial shape of your model and
then convert it to a mesh for further modeling. Meta objects are also very efficient for ray-tracing.

.. note::

   *Meta* objects have a slightly different behavior in *Object Mode*.


Visualization
=============

In Object Mode, the calculated mesh is shown, along with a black "selection ring" (becoming pink when selected).

.. _fig-meta-ball-example:

.. figure:: /images/metainfluenceandselection.jpg
   :width: 350px

   Meta Ball example.


In *Edit Mode* (Fig. :ref:`fig-meta-ball-example`), a meta is drawn as a mesh (either shaded or as black wireframe,
but without any vertex of course), with two colored circles: a red one for selection (pink when selected),
and a green one for a direct control of the meta's stiffness (light green when active).
Note that except for the *Scale* :kbd:`S` transformation,
having the green circle highlighted is equivalent to having the red one.