The SDO-Toolbox is a CLI Application and collection of libraries written in the Rust Programming Language.
The main user-facing feature of the toolbox is a library and CLI application
that can convert SDO files into PDF files. To make this possible, the
toolbox contains a custom PDF writing library that is in some ways the
opposite of, but also prototype for an extension to
This library implements some subset of the PDF standard that allows us to create valid PDF documents with embedded Type3 bitmap fonts (converted from the Signum! printer fonts) and fine grained control over the position of each character on the page.
This also allows us to delay the conversion to Unicode codepoints to the PDF viewer and to keep the encoding of the Signum! fonts.
Spec: PDF 32000-1:2008 (v1.7)
The code that is used to load the signum files into memory does not depend on the rest of the system. This crate contains the datastructures and parser code for Signum!-related file formats.
There is no definitive spec for that file format and the implementation is best-effort and may not always work correctly. It also requires some driver like sdo-tool to be really useful as it does not attempt to combine the formats. For example, it does not attempt to load charset files to get a glyph for some letter in the text.
Part of the SDO-Toolbox is an encoder (and decoder) for the CCITT Group 4 monochrome bitmap coding scheme, that was created for fax machines and is used in PDFs to store small monochrome bitmap images. SDO-Toolbox uses that to transform an Signum! Printer font file into an Adobe Type3 font to be used in generated PDF files.