Add-ons

Blender add-ons development code reuse with symbolic links

Nikita

In the development of add-ons, their modules should be abstracted as much as possible. For a very simple reason – functional, created for a current add-on, will likely need in the next add-on, and possibly not even in one. In the add-on release, the problem of accessing to such common functionality modules is easily solved – all the necessary modules are included in a single package and distributed together. However, during the add-ons development, such modules are much easier to store separately, in one instance, without associating them with any particular package, and import if necessary the desired modules to the desired add-on.

Using symbolic links in the add-ons development
Using symbolic links in the add-ons development

In accordance with the packages import rules, Python allows to refer modules in the following ways:

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Creating multifile add-on for Blender

Nikita

In the development of complex add-ons with large code volume storing all the code in a single file is inappropriate. When a single file contains logically unrelated classes, functions, and datasets, it is difficult to read, debug, find the necessary code pieces, reuse code. Such code layout is considered as very bad programming tone.

Blender Python supports modular system that allows subdividing logical code parts of the add-on into different files, and then connect them to use. Even if you have never thought about modules, creating scripts or add-ons, you have already used them – any code stored in the *.py file is a separate independent module. Just your addon consists of only one module. Complex add-ons may consist of several tens of modules.

Multifile add-on
Multifile add-on

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How to check errors if Blender closes together with system console window

Nikita

Sometimes when debugging scripts or add-ons, errors not only interrupt the code execution but also causes the complete closure of Blender together with its system console. This case its impossible to check errors and view errors messages.

To find a failure, Blender can be started from the command line interpreter cmd. In this case, Blender output log is redirected to the cmd window which, when the program falls due to errors, not closed. If Blender closes all error messages stay available to check in the cmd window.

Running Blender from command line interpreter cmd
Running Blender from command line interpreter cmd

To start Blender from a command line interpreter:

  1. Start the interpreter ( “Start” – Run – cmd)
  2. In the cmd window type the full path to the installed Blender. For example: C:\”Program Files”\blender-2.78a-windows64\blender.exe

Part of the way contains spaces must be enclosed in double quotes – like “Programm Files” in this example.

Accurate Render Border add-on

Nikita

Blender add-on allows setting accurate coordinates for render border.

After add-on installation in T-bar additional “ARB” tab appears. On this tab, it’s possible to set accurate values for left-top and right-bottom render border corners coordinates in pixels. Coordinates establish relative to the render size (Properties — Render — Dimensions — Resolution). After pressing the “Set Accurate Render Border” button render border determines in accordance with the entered values.

Add-on is free and open-source. If you want to support it – you can buy the add-on for a convenient price, or set the price to 0 to download it for free.

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Creating Blender Add-ons variables with values saved in blend-files

Nikita

All user-defined classes (panels, operators), registered in Blender API, exists only during Blender runs. After program close they are deleted from memory. Therefore, if some variables are defined in user classes, all of them will be reset after Blender restart.

However, sometimes it is necessary to use in Blender add-on variables with values that not be lost in the process of program restarting. To retain variables values, it needs to wrap them into special class – property, and attach to any object whose properties are stored in * .blend file.

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Creating panels for placing Blender add-ons user interface (UI)

Nikita
3 Comments / Blender 3D / /

One of the essential conditions of comfortable work is the convenience and speed of accessing add-ons functional. It is not enough to write an add-on and register it in Blender API system. Be sure to give the easy call add-on functions ability to the user. So, any add-on should determine a place to put interface buttons that provide access to its functionality.

This tutorial is for Blender 2.79 and older. For the last Blender versions, please see this tutorial.

All available Blender user interface located on panels. Three panels are the most used: T-bar – opens/hides by pressing the t keyboard button, N-bar – opens/hides by pressing the n button, and the Properties panel – called in the main menu of any window, typed it as Properties.

Blender API allows defining users panels to place add-on functional buttons on any of these three main panels.

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Creating Blender add-on

Nikita
3 Comments / Blender 3D / /

Blender scripting system provides lots of opportunities to simplify and accelerate the workflow, allowing to outsource routine operations to the system and expanding work opportunities through access to the scripting language. However, writing a good script which can be used frequently in various projects, uncomfortable each time to reconnect it to each new project. In addition, this script can be improved with some windows and editable parameters fields. Making complete add-on from the script, you can expand it with additional functionality and connect to the Blender add-ons system.

User-created Blender add-on
User-created Blender add-on

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Installing add-ons to Blender

Nikita
2 Comments / Blender 3D / /

From a certain time to improve work speed and convenience it is necessary to have some functionality that does not exist in the base Blender. To improve its capabilities Blender community users wrote a lot of extras – add-ons. The required add-ons can be purchased or free downloaded from specialized Internet sites. After receiving the necessary add-on, it needs to make a few steps to install it to the Blender program.

For example, let’s install to the Blender add-on allowing to make wireframe render by pressing a certain key combination.

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