A human-readable Type2 Charstring to bytecode converter

A simple converter for Type2 charstrings in human readable and byte form

In Node.js source code

Install with npm install type2-charstring, then use it in your code as:

var convert = require('type2-charstring');
var charstring = convert.toBytes([
]);

In the browser

Use the convert.js from the repo:

<script src="convert.js"></script>
<script>
  var charstring = Type2Convert.toBytes([
  ]);
</script>

API

The following functions are exposed:

• bindSubroutine: function(functor, bytes), binds a global subroutine (to do this from human readable form, run the code through .toBytes and then bind that to a name). The functor can be used in subsequent charstrings to autoresolve to the right subr, so:

bindSubroutine("sin()", [.....]);
// we can now use sin() as charstring code:
var ncs = "3.1415 sin() endchar";
var ncsBytes = Type2Convert.toBytes(ncs);

• getSubroutines: function(), returns the list of global subroutines known until now, with bias correction applied. Generally useful if you need to actually build a font based on the charstrings you've been creating.

• toBytes: function(string, subroutines), converts a human readable charstring to byte form. White space and commas are treated as non-semantic, and line comments are stripped, so you can write properly readable code:

...

// When we start the stack contains: [angle, ox, oy, x, y],
// so we put them onto the transient stack in argument order:
4 put, 3 put, 2 put, 1 put, 0 put

// compute the sin(x) and cos(x) of the provided angle
0 get, sin(x), 5 put
0 get, cos(x), 6 put
...

• toString: function(bytes, subroutines), converts a sequence of bytes into human readable charstring code, but not currently implemented

Dev work

Clone the repo, then install with npm install.

Tests can be run with npm test, and currently cover validation of three functions:

• sin(x)
• cos(x), with a dependency on sin(x)
• rotate(angle, ox, oy, x, y), with a dependency on sin(x) and cos(x)

Why?

I needed a way to write Type2 functions and automatically build them into subroutines.