man aewan (5): File format documentation

INTRODUCTION

Starting with version 0.9.0, Aewan features an all-new, easier to parse file format. Prior versions used a binary (largely undocumented) file format, and relied on a program (ae2aes) to convert it to a readable format. With the new format, the ae2aes utility became unnecessary and was deprecated.

An aewan document is a gzipped file. Therefore, you must first gunzip it in order to be able to parse its contents. On the command line, you could use zcat or something of the sort. On a program, you will probably want to use the zlib library.

In the future it might be better for Aewan to supply a shared library to enable parsing of aewan files with minimal effort. Such a library would have to be integrated with the editor in order not to have to duplicate code (i.e. the editor itself would be just a client of the library). But for the time being, you have to read and parse the format on your own.

FILE FORMAT

In the description below, the items in between brackets are NOT literal, they are placeholders. [S] is a placeholder for a string and [N] is a placeholder for a decimal integer, and [B] is a placeholder for a boolean value ('true' or 'false'). A line with "..." is not literal either, it just means that the lines above repeat a certain number of times.

<Aewan Document v1
   layer-count: int: [N]
   meta-info: str: [S]
   <Layer
        name: str: [S]
        width: int: [N]
        height: int: [N]
        visible: bool: [B]
        transparent: bool: [B]
        layer-line: str: [S]
        layer-line: str: [S]
        layer-line: str: [S]
        (...there are <height> such lines...)
   >Layer
   (...there are <layer-count> such blocks...)
>Aewan Document v1
Indentation is ignored, but all other whitespace is significant.
In particular, you can't omit the space that immediately follows
the ':' field delimiters, or supply more than one space there.
Notice that the file format does not use any quotation marks
for the values, not even strings.

REPRESENTATION OF STRINGS

Strings are represented almost literally in the file (where the [S] placeholders are in the blueprint above), and are not put in between quotes or anything. However, special characters (ASCII codes 1 to 31) are escaped: the escape code is a backslash, followed by the character '0' + ch, where ch is the special character. Thus, a newline character would be represented by "\:", since ":" is '0' + 10.

REPRESENTATION OF INTEGERS AND BOOLEANS

Integers use just the plain old decimal representation. The booleans are represented as strings: either "true" or "false" (without quotes).

REPRESENTATION OF LAYER LINES

Each layer-line is a string, but it is specially formatted in order to convey the characters and attributes in that line. In order to understand the format of a layer-line string, it is first necessary to introduce the concept of cells. A cell in an aewan layer is each of the spaces that can contain a character. A cell has two pieces of data: the character that is in it, and a color attribute. The character is just that: an 8-bit value represing the character drawn there. The color attribute is an 8-bit unsigned value that packs the foreground and background color of a given cell, as well as standout and blink attributes.

The following color codes are used: 0=black, 1=red, 2=green, 3=yellow, 4=blue, 5=magenta, 6=cyan, 7=white.

The 8 bits of the attribute have the following meanings: SFFFLBBB. Where S is the standout bit, FFF is the 3-bit color code for the foreground color, L is the blink bit, and BBB is the 3-bit color code for the background color.

The layer-line string is composed of the hexadecimal representation of layer_width*2 bytes. Each 2 bytes is the information for one cell of the line: the first byte is the character, and the second is the attribute. For example, the hex representation for 'A' is 0x41, so a line with five 'A's each of them in a different foreground color (but all with black background) would be represented as 41104120413041404150.

LICENSE INFORMATION

This program is licensed under the GNU General Public License, version 2 or, at your option, any later version. For full license information, please refer to the COPYING file that accompanies the program.