Python Script :
Modifying a Square Mesh ,
Creating a square in Blender does not set
any problem : Space Bar, then Mesh and finally
The software automatically inserts the object at the exact location of
Just try to imagine for a moment that,
thanks to Python, it is possible to be released from the constraint of
the cursor and for us to create this square anywhere in space by providing
the appropriate co-ordinates. It is, perhaps, a little more complicated
than some clicks of the mouse using the traditional method.
In this tutorial you will learn how
- to create a Python script file
- to import a module,
- to create an object "mesh",
- to access and modify the data corresponding
to the nodes of this "mesh".
To create the
Python script file " test.py":
||Switch to the text editor: Shift-F11.
||Click the button of the datablock browser
(the small square with a white dash "-")
||Select ADD NEW, you now have
an active page in which it is possible to add text, this text could be
carried out by the combination of ALT-p keys .
||Modify the file name to be saved later,
click the button [ TX:Text ], and replace this text with " test.py
|| The cursor of the text window is
red. At its current location, type the following, being sure not to enter
any leading spaces :
Do not leave any space after the last letter
either. Press the [ Enter ] key. This line indicates to Python that
it must load the Blender module which contains the various modules
which, themselves, contain the methods and data fields which make it possible
to interact with the objects and the software commands.
It is necessary to imagine the Blender
module like a set of Russian "nested" dolls. At the interior, different
modules are locked up which contain methods and properties, which may also
be referred to as data fields. The methods make it possible to access and
modify the properties.
|| On the following line add:
|from Blender import NMesh
this line avoids burdening the text by
having to continually type references to the principal module. Without
it, you would be required to write repeatedly: " Blender.NMesh.references
an object " Mesh "
|| The NMesh module contains a method,
which we must use to create an object "mesh" in memory. This object is
created in a buffer.
Note that this object can contain the copy
of another mesh which is already in the scene if one passes the exact name.
Example: me=GetRaw('mesh.001') , will place in memory a working
copy of "mesh.001" which we will be able to access
by using the name "me".
On the third line add:
|How to access
the "mesh" and modify it
||"me" is a mesh object. This object contains
methods and properties. For the moment the properties are empty. No data
exists to work with. Before starting to operate at this level, it is wise
to understand how information dealing with the shape of the mesh objects
is managed in 3D software .
At the base level, there are vertices.
These vertices, therefore, are grouped in an ordered unit, a list,
a single-dimensional array. Its starting index is zero, like the
arrays in the C language. Thus, there is the vertices [ 0 ], then the vertices[
1 ] and the vertices[ 2 ], etc. The index of the last vertex is [ the number
of vertices - 1 ]. Each vertex, itself, consists of an array , another
list , with three inputs containing the co-ordinates x,
y, and z.
y[1.0], z[0.0 ] }
y[1.0], z[0.0 ] }
z[0.0 ] }
y[-1.0], z[0.0 ] }
y[-1.0], z[0.0 ] }
Example of a series of vertices
Geometrically, the faces are made up from
the vertices. Also, they have several properties. Most significantly:
vertices list, a array which references addresses
of the coordinates of the vertices. In Blender, faces can have 3 or 4 vertices.
In other software, the limit of the number of vertices per face can be:
65000, which leaves one to dream.
Example of a series of faces
Let us clarify our objective: create a
mesh to form a face. We will not try to assign a color. In the current
situation, we have started from scratch. The proper order of steps to perform
are as follows : we should initially indicate that the material is not
of type sticky and that the mesh does not have colored
faces. Then it is necessary for us to build a list of vertices, and finally,
use these vertices to manufacture faces.
The procedure for the creation of a vertex,
which is very indirect, is performed in two phases.
Phase 1 / a vertext object
is created in memory using the method NMesh.Vert() .
This method receives as arguments between its parentheses, the parameters
which correspond to the 3D coordinates of the vertex.
Phase 2 / the vertex is added to
the vertices list of "me" which is named "verts"
using the standard Python method for adding an element to a
list : "append()". In Python, the lists are objects
which have methods and properties.
We repeat this operation a sufficient
number of times to create, at last, a face:
The creation of the face is almost identical.
There is an additional phase because it is necessary to fill the list with
vertices of the face before adding it to "me" .
Phase 1 / Creation of a face object
"f" in memory with the method "NMesh.Face()"
Phase 2 / Filling of the face with
the addresses of the vertices co-ordinates. These addresses are preserved
in a list which is simply called "v" .
Phase 3 / we add "f"
the faces list of "me "
The last step of our mesh creation procedure
is to introduce this new object into the objects list of the current
Blender scene by using the method "PutRaw(mesh, [name, renormalise])"
the NMesh module. The associated parameters are the mesh name, which we
worked on, and the "name" which it should have in the Blender object
list. The last parameter forces Blender to recompute the normal vector
on each node.
|NMesh.PutRaw(me, " plane", 1)
Finally, we ask Blender to update
the screen by redrawing it with the new object.
The magic combo: ALT-p and voila,
miracle of miracles, a square has just emerged on the screen!!
Another combo: ALT-s and the save
file window appears. It is now possible to give a name to the text file
by replacing the "current_file_name.blend"which
was automatically displayed, with "test.py"
See the complete squaremesh.py
||Before jumping to the explanation of the
"tesselate.py" file, I would suggest that you manufacture
some "potatoides" by playing with the circular functions and the
equation of the sphere. Which therefore follow, after a little more theory!!
It is not necessary to indicate to Python
what the type of variable is. Whereas, this would be a serious error in
other languages. This small detail reminds one of the good old days
Blender associates other parameters with
the vertices like the "normal" vector , UV coordinates for
texture mapping and the value of the index which is very practical
with the Hash function in editing meshes.
Other properties of the face object:
- the color value, which is coded
in a array with 4 entries: Red, Green, Blue, and Alpha.
- a array of indices, which
references the materials which are used on this face. In Blender, the value
which is located here is sent to another material array, which is
the one used by the mesh object. This is a small technicality with regards
to materials management, upon which we shall not dwell.
To access a particular element of a list
you need to give its number between brackets just after the name.
Example: list_name=[n1,n2,n3,n4] ,
to assign the value of the third element to another variable you
neeed to write: name_variable=list_name, the contents of name_variable
will be n3 . Don't forget, the first element in a list is .