forked from bartvdbraak/blender
172 lines
5.5 KiB
ReStructuredText
172 lines
5.5 KiB
ReStructuredText
..
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This document is appended to the auto generated bmesh api doc to avoid clogging up the C files with details.
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to test this run:
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./blender.bin -b -noaudio -P doc/python_api/sphinx_doc_gen.py -- --partial bmesh* ; cd doc/python_api ; sphinx-build sphinx-in sphinx-out ; cd ../../
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Submodules:
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* :mod:`bmesh.ops`
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* :mod:`bmesh.types`
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* :mod:`bmesh.utils`
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* :mod:`bmesh.geometry`
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Intro
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-----
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This API gives access the blenders internal mesh editing api, featuring geometry connectivity data and
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access to editing operations such as split, separate, collapse and dissolve.
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The features exposed closely follow the C API,
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giving python access to the functions used by blenders own mesh editing tools.
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For an overview of BMesh data types and how they reference each other see:
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`BMesh Design Document <http://wiki.blender.org/index.php/Dev:2.6/Source/Modeling/BMesh/Design>`_ .
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.. note::
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**Disk** and **Radial** data is not exposed by the python api since this is for internal use only.
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.. warning::
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This API is still in development and experimental, while we don't expect to see large changes,
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many areas are not well tested yet and so its possible changes will be made that break scripts.
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*Campbell Barton, 13, March 2012*
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.. warning::
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TODO items are...
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* add access to BMesh **walkers**
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* add custom-data manipulation functions add/remove/rename.
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Example Script
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--------------
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.. literalinclude:: ../../../release/scripts/templates_py/bmesh_simple.py
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Stand-Alone Module
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^^^^^^^^^^^^^^^^^^
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The bmesh module is written to be standalone except for :mod:`mathutils`
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which is used for vertex locations and normals.
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The only other exception to this are when converting mesh data to and from :class:`bpy.types.Mesh`.
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Mesh Access
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-----------
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There are 2 ways to access BMesh data, you can create a new BMesh by converting a mesh from
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:class:`bpy.types.BlendData.meshes` or by accessing the current edit mode mesh.
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see: :class:`bmesh.types.BMesh.from_mesh` and :mod:`bmesh.from_edit_mesh` respectively.
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When explicitly converting from mesh data python **owns** the data, that is to say - that the mesh only exists while
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python holds a reference to it, and the script is responsible for putting it back into a mesh data-block when the edits
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are done.
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Note that unlike :mod:`bpy`, a BMesh does not necessarily correspond to data in the currently open blend file,
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a BMesh can be created, edited and freed without the user ever seeing or having access to it.
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Unlike edit mode, the bmesh module can use multiple BMesh instances at once.
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Take care when dealing with multiple BMesh instances since the mesh data can use a lot of memory, while a mesh that
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python owns will be freed in when the script holds no references to it,
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its good practice to call :class:`bmesh.types.BMesh.free` which will remove all the mesh data immediately and disable
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further access.
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EditMode Tessellation
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^^^^^^^^^^^^^^^^^^^^^
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When writing scripts that operate on editmode data you will normally want to re-calculate the tessellation after
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running the script, this needs to be called explicitly.
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The BMesh its self does not store the triangulated faces, they are stored in the :class:`bpy.types.Mesh`,
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to refresh tessellation faces call :class:`bpy.types.Mesh.calc_tessface`.
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CustomData Access
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-----------------
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BMesh has a unified way to access mesh attributes such as UV's vertex colors, shape keys, edge crease etc.
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This works by having a **layers** property on bmesh data sequences to access the custom data layers which can then be
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used to access the actual data on each vert/edge/face/loop.
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Here are some examples ...
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.. code-block:: python
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uv_lay = bm.loops.layers.uv.active
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for face in bm.faces:
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for loop in face.loops:
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uv = loop[uv_lay].uv
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print("Loop UV: %f, %f" % uv[:])
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vert = loop.vert
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print("Loop Vert: (%f,%f,%f)" % vert.co[:])
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.. code-block:: python
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shape_lay = bm.verts.layers.shape["Key.001"]
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for vert in bm.verts:
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shape = vert[shape_lay]
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print("Vert Shape: %f, %f, %f" % (shape.x, shape.y, shape.z))
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.. code-block:: python
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# in this example the active vertex group index is used,
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# this is stored in the object, not the BMesh
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group_index = obj.vertex_groups.active_index
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# only ever one deform weight layer
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dvert_lay = bm.verts.layers.deform.active
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for vert in bm.verts:
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dvert = vert[dvert_lay]
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if group_index in dvert:
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print("Weight %f" % dvert[group_index])
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else:
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print("Setting Weight")
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dvert[group_index] = 0.5
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Keeping a Correct State
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-----------------------
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When modeling in blender there are certain assumptions made about the state of the mesh.
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* hidden geometry isn't selected.
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* when an edge is selected, its vertices are selected too.
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* when a face is selected, its edges and vertices are selected.
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* duplicate edges / faces don't exist.
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* faces have at least 3 vertices.
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To give developers flexibility these conventions are not enforced,
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however tools must leave the mesh in a valid state else other tools may behave incorrectly.
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Any errors that arise from not following these conventions is considered a bug in the script,
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not a bug in blender.
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Selection / Flushing
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^^^^^^^^^^^^^^^^^^^^
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As mentioned above, it is possible to create an invalid selection state
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(by selecting a state and then de-selecting one of its vertices's for example), mostly the best way to solve this is to
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flush the selection after performing a series of edits. this validates the selection state.
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Module Functions
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----------------
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