Sophie: blender-manual-2.49a-1ark i586

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>Blender Documentation Volume I - User Guide: Last modified April 29 2004 S68</TH
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><H1
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><A
NAME="mesh_modeling_metabals"
></A
>Meta Objects</H1
><P
>&#13;      Meta Objects consist of spherical, tubular and cuboidal elements that can affect
      each other's shape. You can only
	create rounded and fluid 'mercurial',
      or 'clay-like', forms that exist <I
CLASS="emphasis"
>procedurally</I
>,
	that is are computed dynamically. Use
	Meta Objects for special effects or as a basis for modelling.
	</P
><P
>&#13;		Meta Objects are also called <I
CLASS="emphasis"
>implicit surfaces</I
>,
		again to point out that they are not <I
CLASS="emphasis"
>explicitly</I
>
		defined by vertices (as meshes are) or control points (as
		surfaces are).
	</P
><P
>&#13;		Meta Objects are defined by a <I
CLASS="emphasis"
>directing structure</I
>
		which can be seen as the source of a static field. The
		field can be either positive or negative and
		hence the field generated by neighbouring directing structures
		can attract or repel.
	</P
><P
>&#13;		The implicit surface is defined as the surface where the 3D field generated
		by all the directing structures assumes a given value. For
		example a Meta Ball, whose directing structure is a point, generates an isotropic
		field around it and the surfaces at constant field value are spheres
		centered at the directing point.
		Two neighbouring Meta
balls interact
		and, if they are close enough, the two implicit surfaces merge into a single
		surface (<A
HREF="x3321.html#BSG.EDT.F.S68.1201"
>Figure 68</A
>).
	</P
><DIV
CLASS="figure"
><A
NAME="BSG.EDT.F.S68.1201"
></A
><DIV
CLASS="mediaobject"
><P
><IMG
SRC="PartM/mesh_modeling/gfx/MetaBall01.png"></P
></DIV
><P
><B
>Figure 68. Two Metaballs</B
></P
></DIV
><P
>&#13;      In fact, Meta Objects are nothing more than mathematical formulas that
      perform logical operations on one another (AND, OR), and that can be
      added and subtracted from each other. This method is also called CSG,
	Constructive Solid Geometry.  Because of its mathematical nature, CSG
	uses little memory, but requires lots of CPU to compute. To optimize this
	the implicit surfaces are <I
CLASS="emphasis"
>polygonized</I
>.
	The complete CSG area is divided into a 3D grid, and
      for each <I
CLASS="emphasis"
>edge</I
> in the grid a calculation is made, and
	if (and more
      importantly where) the formula has a turning point, a 'vertex' for the
      <I
CLASS="emphasis"
>polygonize</I
> is created.
</P
><P
>&#13;	To create a Meta Object press <B
CLASS="keycap"
>SPACE</B
> and select
	<TT
CLASS="literal"
>Add&#62;&#62;MBall</TT
>. You can select the base shapes:
	Ball, Tube, Plane, Ellipsoid and Cube.
</P
><P
>&#13;	MetaBalls have a point directing structure, MetaTubes have a segment as a directing structure,
	MetaPlanes a plane, and MetaCubes a cube. The underlying structure
	becomes more evident as you lower the <TT
CLASS="literal"
>Wiresize</TT
> and raise the <TT
CLASS="literal"
>&#13;	Threshold</TT
> values in the <TT
CLASS="literal"
>Meta Ball</TT
> Panel.
</P
><P
>&#13;      When in EditMode, you can move and scale the Meta Objects as you
      wish. This is the best way to construct static - as opposed to animated -
	forms. Meta Objects can also influence each other <I
CLASS="emphasis"
>outside</I
>
	EditMode. When outside EditMode you have much more freedom; the balls can rotate
	or  move and they get every <I
CLASS="emphasis"
>transformation</I
> of the
	Parent Objects. This method requires more calculation time and is thus somewhat slow.
</P
><P
>&#13;      The following rules describe the relation between Meta Objects:
</P
><P
></P
><UL
><LI
STYLE="list-style-type: opencircle"
><P
>&#13;            All Meta Objects with the same 'family' name (the name
            without the number) influence each other. For example "MBall",
            "MBall.001", "MBall.002", "MBall.135". Note here that we are not
		talking about the name of the MetaBall ObData block.
      </P
></LI
><LI
STYLE="list-style-type: opencircle"
><P
>&#13;            The Object with the family name <I
CLASS="emphasis"
>without</I
> a
		number determines the
            basis, the resolution, <I
CLASS="emphasis"
>and</I
> the transformation
		of the polygonize. It
            also has the Material and texture area and will be referred to as <I
CLASS="emphasis"
>base</I
>
		Meta Object.
      </P
><P
>&#13;      	Only one Material can be used for a Meta Object set.
	      In addition, Meta Objects save a separate texture area; this
      	normalises the coordinates of the vertices. Normally the texture area
	      is identical to the <I
CLASS="emphasis"
>boundbox</I
> of all vertices. The
		user can force a
	      texture area with the <B
CLASS="keycap"
>TKEY</B
> command (outside of EditMode).
	</P
><P
>&#13;		The fact that the base Object dictates the polygonalization
		implies that, if we have two Meta Objects and we move one of them
		we will see the polygonalization of the <I
CLASS="emphasis"
>non-base</I
>
		Object change during motion, regardless of which of the two object is actually moving.
	</P
></LI
></UL
><P
>&#13;	The <TT
CLASS="literal"
>Meta Ball</TT
> Panel in Editing context offers few settings.
	If in Object Mode, only this Panel is present. You can define the polygonalization
	average dimension both in the 3D Viewport via the <TT
CLASS="literal"
>Wiresize</TT
>
	Num Button, and at rendering time via the <TT
CLASS="literal"
>Rendersize</TT
>
	Num Button. The lower these are, the smoother the Meta Object is, and the slower
	its computation.
</P
><P
>&#13;      The <TT
CLASS="literal"
>Threshold</TT
> Num Button is an important setting for
      MetaObjects. It controls the 'field level' at which the surface is computed.
	To have finer control, when in EditMode, the <TT
CLASS="literal"
>Stiffness</TT
>
	Num Button of the <TT
CLASS="literal"
>Meta Ball Tools</TT
> Panel allows you to enlarge
	or reduce the MetaObject's field of influence.
</P
><P
>&#13;	In this latter Panel you can also change the Meta Object type and
	set it negative (that is subtractive, rather than additive) with other
	Meta Objects of the same set.
</P
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