# 9. Design Notes¶

## 9.1. General Design¶

### 9.1.1. Coding Philosophy¶

Musica tries to provide a clean oriented object API rather than a set of macros.

In particular, for efficiency and readability reasons, we distinguish API docstrings and user guide, and unit tests leave in separated files.

As Donald Knuth written, “Premature optimisation is the root of all evil (or at least most of it) in programming”. Thus further optimisations must be motivated by code profiling.

We use the last features of the Python language, thus we require an up to date Python 3 interpreter.

### 9.1.2. Internationalisation¶

Musica supports Latin and English conventions, internationalisation of music therms is provided by gettext.

Musica also try to be independent of the Western music system.

### 9.1.3. Music Theory Implementation¶

Musica implements the western music system from its mathematical foundation. It means the music system is mostly generated automatically rather than hardcoded in the source. For example, the twelve-tone equal temperament is just defined by 12 tones, 7 natural notes (C, D, E, F, G, A, B) and A440 as reference pitch. The distribution of the notes is then determined from Pythagorean and equal temperament theory. See the module Musica.Math.MusicTheory for further details.

### 9.1.4. Figure Generation¶

The best actual open formats for figures are PDF (Portable Document Format) and SVG (Scalable Vector Graphics). PDF and SVG are quite similar regarding the way to describe graphics, but they serve two different purposes. PDF is a binary format optimised for printed document rather than SVG is based on XML and thus well suited for application inter-exchanges and web technologies. XML is an advantage of SVG over PDF, since it is easier to write XML than to deal with a binary format. For the same reason, it is easier to modify an SVG document than a PDF document.

In practice, we need both formats, depending if we want to make a printable document or create a web content. But this is not an issue, since we can convert a document from PDF to SVG, and vice versa. We can thus imagine to generate a high quality document in PDF and then convert it to SVG.

If we want to generate scores or parts of scores, then the best solution is to use the LilyPond engraving program. However Lilypond is not well suited when we want a full control of the layout, in this case a basic engraving system is more adapted.

To generate high quality figures, we need these components:

• a basic geometry engine to compute coordinates,
• a text engine to format advanced text,
• a graphic engine to abstract a low level API like SVG or PDF,
• a library to write PDF or SVG.

There are several solutions to achieve this. We could simply generate XML from Python, but a text engine like LaTeX is unrivalled, especially as we cannot use the power of HTML and Mathjax. We could also use a graphic library, like the vector graphics language and processor Asymptote , or the ReportLab open-source PDF Toolkit. Note that Asymptote uses internally LaTeX to generate labels.

Another solution is to use the power of LaTeX in combination with the package TikZ/PGF, a graphic systems for TeX, and the Emmentaler font from the Lilypond project. This solution provides a text engine and a graphic engine which abstract the PDF format.

Up to now, any TeX engine is able to generate directly SVG, but we have several possibilities to get it. We can convert PDF to SVG using pdf2svg, MuPDF or Inkscape. But we have a more direct path using the dvisvgm tool which convert DVI to SVG, since PGF has a driver for dvisvgm.

Despite TeX was developed in 1978, many developers continue to improve and update it. Recently the LuaTeX engine provides an interesting alternative to pdfTeX and new features that benefit to PGF.

Another advantage of the TeX approach, is to provide an output in TeX/PGF which provides a description of the figure in a graphic language that can be modified in an editor and then a SVG output which can be modified in an GUI SVG editor like Inkscape. Despite the inherent complexity of TeX/PGF, a tools like Inkscape is poorly adapted to make technical figures.

In conclusion, the approach to make figure in Musica provides three levels of description: the Python level, the TeX/PGF level and finally the SVG level.

### 9.1.5. MusicXML¶

MusicXML is an open format to describe scores.

The best approach to handle the MusicXML format is to generate automatically codes from the XML schema.

## 9.2. Coding¶

### 9.2.1. Copy constructor¶

foo = Foo(...)

bar = Foo(foo)       # C++ style
bar = foo.clone()    # generic interface, don't ensure a particular type
bar = Foo.clone(foo) # ensure type