Python – Blender – Interplanety

Drawing in Blender viewport

The Blender 2.80 API provides an ability to draw in a viewport (3D Viewport) using the “gpu” module.

As an example let’s draw a simple coordinate system widget in the center of the scene, consisting of three lines with different colors.

Continue reading “Drawing in Blender viewport”

Calling functions by pressing buttons in Blender custom UI

Button click in basically connected with the operator calling in Blender user interface. However, some times actions, that need to be performed when a button is pressed, are quite simple and do not require a separate operator for them. And it makes no sense to fill a registered operators stack with a multitude of specific operators designed to perform one highly specialized function. It would be much more convenient to associate a button press with a separate function call but the Blender API allows to associate buttons only with an operator call.

To solve the problem of creating a separate operator for each button we can use the fact that the operator can be called with the input parameters.

Continue reading “Calling functions by pressing buttons in Blender custom UI”

How to get a list with all possible values of an EnumProperty

To correctly set values to an EnumProperty type we need to know all its possible entries.

If we try to set a value to an EnumProperty that is out of its available variants, Blender will throw an error:

TypeError: bpy_struct: item.attr = val: enum “xxx” not found in (‘value_001′, value_002’, …)

where:

xxx – the value we tried to set to an EnumProperty

value_001, value_002, … – possible EnumProperty values

Continue reading “How to get a list with all possible values of an EnumProperty”

How to move cursor to vertex

To translate cursor to the desired mesh vertex execute the following code:

bpy.context.scene.cursor.location = bpy.context.object.matrix_world @ bpy.context.object.data.vertices[_VERTEX_NUMBER_].co

1	bpy.context.scene.cursor.location = bpy.context.object.matrix_world @ bpy.context.object.data.vertices[_VERTEX_NUMBER_].co

Attention to the multiplication order – world matrix should be left.

How to link a new object to a scene in Blender 2.80 Python API

In Blender 2.79 Python API we can add a new object to a scene with:

bpy.context.scene.objects.link(new_object)

1	bpy.context.scene.objects.link(new_object)

If we try to do this in Blender 2.80, it throws an error:

‘bpy_prop_collection’ object has no attribute ‘link’

In Blender 2.80 API new objects mast be linked not to the scene, but to the scene collections:

To link a new object to the active scene collection:

bpy.context.scene.collection.objects.link(new_object)

1	bpy.context.scene.collection.objects.link(new_object)

To link a new object to the collection by its name:

bpy.data.collections['collection_name'].objects.link(new_object)

1	bpy.data.collections['collection_name'].objects.link(new_object)

How to move the cursor to the active strip start/end position in Blender VSE

To move the cursor to the start position of the active strip in Blender VSE:

bpy.context.scene.frame_current = bpy.context.scene.sequence_editor.active_strip.frame_start

1	bpy.context.scene.frame_current = bpy.context.scene.sequence_editor.active_strip.frame_start

To move the cursor to the end position of the active strip:

bpy.context.scene.frame_current = bpy.context.scene.sequence_editor.active_strip.frame_final_end

1	bpy.context.scene.frame_current = bpy.context.scene.sequence_editor.active_strip.frame_final_end

Executing operators with parameters

When making your own custom operators, sometimes it is necessary to pass them certain values – execute operator with parameters.

The passed parameter must be defined as an operator property.

Continue reading “Executing operators with parameters”

Transfer selection from the UV-map to mesh

The UV-map is directly linked to the mesh through meshloops. We can use that to transfer the selection from the UV-map to the mesh.

To transfer the selection from the UV-map to the mesh, we need to cycle through the mesh polygons, check which meshloops are selected and select the corresponding vertices on the mesh itself.

Continue reading “Transfer selection from the UV-map to mesh”

How to get vertices from Vertex Group by its name

To get a list of vertices from the vertex group by its name we can use the following code:

[vert for vert in bpy.context.object.data.vertices if bpy.context.object.vertex_groups['vertex_group_name'].index in [i.group for i in vert.groups]]
# [bpy.data.meshes['Cube'].vertices[0], bpy.data.meshes['Cube'].vertices[1], ...

1 2	[vert for vert in bpy.context.object.data.vertices if bpy.context.object.vertex_groups['vertex_group_name'].index in [i.group for i in vert.groups]] # [bpy.data.meshes['Cube'].vertices[0], bpy.data.meshes['Cube'].vertices[1], ...

Creating points on a Bezier curve

Bezier curves are drawing by four points: two main points (p0, p1) and two handle points (p0_hr, p1_hl).

To add an additional point p2 to a curve at a moment t, with t changes from 0 to 1 and represents the ratio of the p2 point location to the total length of the curve, we need to do the following:

Continue reading “Creating points on a Bezier curve”

Fake-bpy-module

Code autocomplete greatly simplifies writing scripts or developing add-ons for Blender. One of the best autocomplete modules for today is developed by Nutti. Last updated 20190718.

The project is hosted on the author’s GitHub: https://github.com/nutti/fake-bpy-module

The modules are distributed via pip or as a pre-generated-modules. Author also provides a module generator with which you can assemble autocomplete modules yourself.

Decorators for node tree updation delay

When we create a field on the add-on interface panel, the value of which changes something in the node tree, each time the user changes the field value the node tree recompiles. If the user changes the value in that field by holding and moving the mouse, too frequent node tree recompilation will cause Blender to hangs.

This problem can be solved using decorators for deferred updating of the node tree.

Code by Skarn.

Continue reading “Decorators for node tree updation delay”

Class for creating nodes by type

Class for quick node creation by their type.

Code by Skarn.

class NodeTreeBuilder:

    def __init__( self
                 , node_tree : bpy.types.NodeTree
                 , x : float = -200
                 , y : float = -200
                 , delimeter : float = 300
                ):
        self._x = x
        self._y = y
        self.tree = node_tree
        self.delimeter = delimeter

        self.purge_tree()

    def purge_tree(self):
        for node in self.tree.nodes:
            self.tree.nodes.remove(node)

    def add_node(  self
                 , node_type : str
                 , node_name : str
                 , column : int
                 , row : int
                 , node_descr : str = ""
                ):

        node = self.tree.nodes.new(node_type)
        node.name = node_name
        node.label = node_descr if node_descr else node_name

        node.location = (self.delimeter * column + self._x, -self.delimeter * row + self._y)

        return node

class NodeTreeBuilder:

def __init__( self

, node_tree : bpy.types.NodeTree

, x : float = -200

, y : float = -200

, delimeter : float = 300

self._x = x

self._y = y

self.tree = node_tree

self.delimeter = delimeter

self.purge_tree()

def purge_tree(self):

for node in self.tree.nodes:

self.tree.nodes.remove(node)

def add_node( self

, node_type : str

, node_name : str

, column : int

, row : int

, node_descr : str = ""

node = self.tree.nodes.new(node_type)

node.name = node_name

node.label = node_descr if node_descr else node_name

node.location = (self.delimeter * column + self._x, -self.delimeter * row + self._y)

return node

Continue reading “Class for creating nodes by type”

How to protect your add-on from downloading through aggregators

With the Blender popularity growing, the number of add-ons created for it by third-party developers is growing too. A lot of high-quality professional add-ons are written for Blender now. Over time, the number of add-ons is becoming more and more. And on this wave aggregators appeared – programs and services independently searching for add-ons and allowing Blender users to install add-ons quickly, many at once, and bypassing add-on distribution channels selected by their authors. What caused a negative reaction of add-on developers.

Continue reading “How to protect your add-on from downloading through aggregators”

How to detect if Local View is on in 3D View window

The following command returns the 3D View areas list with enabled Local View mode:

[area for area in bpy.context.screen.areas if area.type =='VIEW_3D' and area.spaces[0].local_view]

# [bpy.data.screens['Layout']...Area]

[area for area in bpy.context.screen.areas if area.type =='VIEW_3D' and area.spaces[0].local_view]

# [bpy.data.screens['Layout']...Area]

Changing objects visibility in the viewport and while rendering

The easiest way to hide and show rendering objects is to assign animation keys to them. To do this, move the cursor over the eye icon (visibility in the viewport) or camera (visibility when rendering) in the Outliner window, press the “i” key and then manage the created condition in the Graph Editor like the ordinary animation keys.

But this method is not always available. For example, we cannot assign visibility animation keys for collections, Blender will generate errors like:

“hide_viewport” property cannot be animated

“hide_render” property can not be animated

However, using the Blender Python API, we can control the visibility of such objects.

Continue reading “Changing objects visibility in the viewport and while rendering”

Blender autocomplete modules

Nutti, the author of the “fake-bpy-modules” project, has made the installation of the Blender Python API autocomplete modules through the pip platform. Pip installation is faster and easier, but sometimes we just need to copy the autocomplete modules to our project but now they are not included in the Nutti’s GitHub.

Copies of the autocomplete modules for Blender versions 2.79 and 2.80 can be downloaded directly from here: https://github.com/Korchy/blender_autocomplete

How to get global vertex coordinates

To get the vertex coordinates in the scene global coordinate system when the object’s scale was not applied, we need to multiply the local vertex coordinates by the object world transformation matrix:

object = bpy.data.objects['_MY_OBJECT_']
v_local = object.data.vertices[_VERT_NUMBER_].co # local vertex coordinate
v_global = object.matrix_world @ v_local # global vertex coordinates

object = bpy.data.objects['_MY_OBJECT_']

v_local = object.data.vertices[_VERT_NUMBER_].co # local vertex coordinate

v_global = object.matrix_world @ v_local # global vertex coordinates

Class naming conventions in Blender 2.8 Python API

In Blender 2.8 API the requirements for the class and their identifiers naming are becoming tougher. The class name must match the following convention:

UPPER_CASE_{SEPARATOR}_mixed_case

1	UPPER_CASE_{SEPARATOR}_mixed_case

Where the {SEPARATOR} is two letters denoting the class belonging to a certain type (from which type the class is inherited):

HT – Header
MT – Menu
OT – Operator
PT – Panel
UL – UI list

The class identifier “bl_idname” mast match the class name.

Continue reading “Class naming conventions in Blender 2.8 Python API”

Changes in add-ons registration through the API in Blender 2.8

Add-on registration and removing were made with the “Window manager” (wm) in Blender 2.7 Python API:

bpy.ops.wm.addon_install(filepath='_path_to_addon', overwrite=True)

bpy.ops.wm.addon_enable(module='addon_name')

bpy.ops.wm.addon_remove(module='addon_name')

bpy.ops.wm.addon_install(filepath='_path_to_addon', overwrite=True)

bpy.ops.wm.addon_enable(module='addon_name')

bpy.ops.wm.addon_remove(module='addon_name')

In Blender 2.8 API add-on operators moved to the “preferences”:

bpy.ops.preferences.addon_install(filepath='_path_to_addon', overwrite=True)

bpy.ops.preferences.addon_enable(module='addon_name')

bpy.ops.preferences.addon_remove(module='addon_name')

bpy.ops.preferences.addon_install(filepath='_path_to_addon', overwrite=True)

bpy.ops.preferences.addon_enable(module='addon_name')

bpy.ops.preferences.addon_remove(module='addon_name')

3D Cursor location in Blender 2.8 Python API

3D-cursor location property

context.scene.cursor_location

1	context.scene.cursor_location

in Blender 2.8 API moved to “cursor” object

context.scene.cursor.location

1	context.scene.cursor.location

When trying to get the cursor location through the “context.scene.cursor_location” Blender throws an error:

‘Scene’ object has no attribute ‘cursor_location’

Add-on preferences panel

When developing add-ons it is often necessary to give an ability to set a number of parameters that affect the whole add-on work to the user. For example, the user can specify a directory for saving/loading files, set some default variables or switch between add-on modes. Of course, the interface for setting such parameters can be placed in the add-on panel, but it is better to place it in a separate add-on preferences panel, which is located in the “Preferences” window under the add-on installation panel.

The main advantage of the add-on preferences is that they don’t reset when Blender restarts. The user does not need to configure the add-on preferences each time, it’s enough to set the necessary parameters once, personalizing the add-on for convenient work.

Let’s create an add-on and define a parameter, placing it in the add-on preferences panel.

Continue reading “Add-on preferences panel”

Matrix, vector and quaternion multiplication in Blender 2.8 Python API

In Blender 2.7 the “*” (star) operator is used in the matrix, vector, and quaternion multiplication. In Blender 2.8 it is replaced with the “@” (at) operator.

If the “*” operator is used in vector, matrix or quaternion multiplication in Blender 2.8 it throws an error:

Element-wise multiplication: not supported between ‘Matrix’ and ‘Matrix’ types

Proper use of the “@” operator:

bpy.context.region_data.view_rotation @ Vector((0.0, 0.0, 1.0))

1	bpy.context.region_data.view_rotation @ Vector((0.0, 0.0, 1.0))

Snapping elements property in Blender 2.8 Python API

The snapping elements property from Blender 2.7

bpy.context.scene.tool_settings.snap_element

1	bpy.context.scene.tool_settings.snap_element

changed in Blender 2.8 API to

bpy.context.scene.tool_settings.snap_elements
# {'EDGE'}

1 2	bpy.context.scene.tool_settings.snap_elements # {'EDGE'}

Accessing the pivot point type in Blender 2.8 Python API

The “pivot_point” property from Blender 2.7

bpy.context.area.spaces[0].pivot_point
# 'BOUNDING_BOX_CENTER':

1 2	bpy.context.area.spaces[0].pivot_point # 'BOUNDING_BOX_CENTER':

in Blender 2.8 API moved to:

bpy.context.scene.tool_settings.transform_pivot_point
# 'MEDIAN_POINT'

1 2	bpy.context.scene.tool_settings.transform_pivot_point # 'MEDIAN_POINT'