Architecture

Boxes.py it structured into several distinct tiers.

User Interfaces

User interfaces allow users to render the different generators. They handle the parameters of Generators and convert them to a readable form. The user interfaces are located in scripts/. Currently there is

• scripts/boxes – the command line interface

• scripts/boxesserver – the web interface

• scripts/boxes2inx – generates Inkscape extensions

• scripts/boxes_example.ipynb – Jupyter notebook

Generators

A (box) generator is a subclass of boxes.Boxes. It generates one drawing. The subclasses overload .__init__() to set their parameters and implement .render() that does the actual drawing.

Generators are found in boxes/generators/. They are included into the web UI and the CLI tool by the name of their class. So whenever you copy either an existing generator or the skeleton in boxes/generators/_template.py you need to change the name of the main class first.

Parts

Parts are a single call that draws something according to a set of parameters. There are a number of standard parts. Their typical params are explained in the API docs.

The only real requirement for a part is that it must support the move parameter for placement.

Part Callbacks

Most parts support callbacks - either one in the middle for round parts or one for each edge. They allow placing holes or other features on the part, independent of edge type. Without using callbacks, you will not have consistent placement of internal features.

Navigation and Turtle Graphics

Many drawing commands in Boxes.py are Turtle Graphics commands. They start at the current position and in the current direction and move the coordinate system with them. This way the absolute coordinates are never used and placement and movement is always relative to the current position.

There are a few functions to move the origin to a convenient position or to return to a previously saved position.

Edges

Edges are turtle graphic commands. But they have been elevated to proper Classes to handle outsets. They can be passed as parameters to parts. There is a set of standard edges found in .edges. They are associated with a single char which can be used instead of the Edge object itself at most places. This allows passing the edge description of a part as a string.

Turtle graphics

There are a few turtle graphics commands that do the actual drawing. Corners with an positive angle (going counter clockwise) close the part while negative angles (going clockwise) create protrusions. This is inversed for holes which need to be drawn clockwise.

Getting this directions right is important to make the burn correction (aka kerf) work properly.

Simple drawing commands

These also are simple drawing commands. Some of them get x, y and angle parameters to draw somewhere specific. Some just draw right at the current coordinate origin. Often these commands create holes or hole patterns.

Back end

Boxes.py used to use cairo as graphics library. It now uses its own - pure Python - back end. It is not fully encapsulated within the drawing methods of the Boxes class. Although this is the long term goal. Boxes.ctx is the context all drawing is made on.