A specification for a FlashInvader exchange format
The street artist known as Invader disposes mosaics originaly inspired by 8 bit videogames all over the world. The mosaics can be flashed and collected in a smartphone application called FlashInvaders.
It is currently not possible to exchange or export the flashed mosaic list
The FlashFile format is a compact format to describe lists of items that can be Invader's mosaics.
The format describes a list of items. Each item has a unique name in the LOCATION_ORDER format.
Example :
NY_100
PA_27
PA_1500
SPACE_02
In this specification we consider lists whose final description is a list of items. Using the complete descrition of an item takes a lot of space and there are opportunities to encode a list in a format that uses much less characters.
The format is text based and consists of a list of token, separated by spaces or newlines.
There can be comments starting from position 0 in a line or within a line provided all tokens in the line are valid.
Comments start with a # and extend to th end of the current line. Comment contents does not contribute to tokens.
Tokens are case sensistive.
Each token describes one or many item.
Example:
# this is valid
PA_1299 LA_18 # MARS_19 is not in the list
A text value, usually a single word or symbol that describes uniquely the location part
Example:
GRTI
A value the describes a single order or a contiguous range of orders.
The range is absolute when the order part contain two numbers separated by a comma (.)
The number before the comma describes the lower bound value of the range and number after the comma describes the upper bound value.
The range is relative when the order part contains a plus (+).
-
The number before he
+sign is the absolute lower bound of the range -
The optional number after the
+sign is the number of consecutive items after the lower bound to consider. When not present is value is set to 1
Exemple:
12 # the item with order 12
43,53 # the items with order from 43 to 53 included
23+3 # the items with order from 23 to 26 included
17+ # the items with order 17 and 18
They define the location part of the item for all following tokens until set by another.
the token is build using a LOCATION, and an ORDER. separated by an underscore _
- token with order part defines the location of the item and sets the implicit location to its location Example:
TK_28
HK_04,10
KAT_10+3
They define the order part of the item for the implicit location.
They can be part of a token with location or be a token on their own. If the token has no LOCATION part, the implicit location is used to resolve the location
The implicit location decides what LOCATION an ORDER only token is attributed to. The implicit location is reset to itself by any of the explicit LOCATION tokens exemple:
FTBL_17
20,22 # means # FTBL_20 FTBL_21 FTBL_22
AMS_12
18 # means # AMS_18
Exemple:
ROM_03 # add ROM_03 to the list, sets ROM as the implicit location and ADD implicit mode
19 27,29 # adds ROM_19 ROM_27 ROM_28 ROM_29 to the list
DIJ_01+5 # adds DIJ_01 DIJ_02 DIJ_03 DIJ_04 DIJ_05 DIJ_06
This format allows for very concise description of mosaics flashed in the world,
-
The compression ratio is vey high compared to a "flat" list of every item
-
It happens that LIL (Lille) is the only invaded location in the world to have its order number start at 0 instead of 1.
-
Order format is specific to Invader , order numbers < 10 have a leading "0", as in NOO_01. leading 0(s) are optional nut it is recommended to use them in flashlists. Example xxx_flashfile_max.txt is no leading 0 and achieves a 1:11.3 compressionnn ratio against reference xxx_flashflat.txt.
FlashFiles are optimized for FlashInvaders but can be used for any Location&Order application.
The format is still very readable while beeing so concise. Any list in the form of complete location is a valid FlashFile, so that compatibility is total with flat format. Even for large lists of flashes, due to the lage compression factor, flashfiles be encoded in a QRCode and shared or sent in mails or messages as plain text,
The format is very simple to parse, as it is separator based with a limited number of tokens and states. A sample implementation is given in Javascript with a decoding tool.
A sample file for flashed mosaics from the Invader universe is provided in flashfile (1244 bytes) and flat (16943 bytes) This describes 2348 mosaics in 46 cities and is the flashlist of one of the top 250 players
To check for correctness on an OS with bash or compatible shell:
node testflashfile.js ../examples/xxx_flashfile.txt
A stand alone HTML dencode/decode tool is implemented in fftool.html with a live demo at