The Editor Charset file format (E24)

Signum! has their very own bitmapped font format which is not documented anywhere that I could find. The basic layout is this:

+-----+-----+-----+-----+
| "e" | "s" | "e" | "t" |
+-----+-----+-----+-----+
| "0" | "0" | "0" | "1" |
+-----+-----+-----+-----+
|       font type       |
+-----+-----+-----+-----+

For all fonts I have tried, the font type is 0x00000010, which is big-endian for 128. That corresponds to the default 7-bit character fonts used in Signum! 1/2.

127-character fonts

The header is followed by 128 bytes of something, which may or may not be related to kerning or guide-rules at font creation.

After that, there is a big-endian 32-bit byte-length specifier for the character data buffer, which is the largest and last part of the file.

After that length, there are 127 BE, 32bit offsets into the character buffer, that correspond to the 127 characters. This may be used for random access to any of the characters.

Finally, there is the character buffer itself, which is a sequence of 4 byte character headers and a variable amount of two-byte character bitmap rows.

+--------+--------+
|  top   | height |
+--------+--------+
| width  |  ???   |
+--------+--------+
|        .        |
+        .        +
|        .        |
+-----------------+

That last character header byte is probably just padding. The number of bitmap rows is height; top indicates the distance of that bitmap from the upper edge of a 24 pixel line and width is the space that should be reserved/skipped to move past this character and draw the next one.

For the mapping between character codes and keys on the keyboard, have a look at the character sets page.