sgt-net — Network jigsaw puzzle

## Synopsis

sgt-net [--generate n] [--print wxh [--with-solutions] [--scale n] [--colour]] [game-parameters|game-ID|random-seed]

sgt-net --version

## Description

(Note: the Windows version of this game is called NETGAME.EXE to avoid clashing with Windows's own NET.EXE.)

I originally saw this in the form of a Flash game called FreeNet (http://www.jurjans.lv/stuff/net/FreeNet.htm), written by Pavils Jurjans; there are several other implementations under the name NetWalk. The computer prepares a network by connecting up the centres of squares in a grid, and then shuffles the network by rotating every tile randomly. Your job is to rotate it all back into place. The successful solution will be an entirely connected network, with no closed loops. As a visual aid, all tiles which are connected to the one in the middle are highlighted.

## Net controls

This game can be played with either the keyboard or the mouse. The controls are:

Select tile: mouse pointer, arrow keys

Rotate tile anticlockwise: left mouse button, ‘A’ key

Rotate tile clockwise: right mouse button, ‘D’ key

Rotate tile by 180 degrees: ‘F’ key

Lock (or unlock) tile: middle mouse button, shift-click, ‘S’ key
You can lock a tile once you're sure of its orientation. You can also unlock it again, but while it's locked you can't accidentally turn it.

The following controls are not necessary to complete the game, but may be useful:

Shift grid: Shift + arrow keys
On grids that wrap, you can move the origin of the grid, so that tiles that were on opposite sides of the grid can be seen together.
Move centre: Ctrl + arrow keys
You can change which tile is used as the source of highlighting. (It doesn't ultimately matter which tile this is, as every tile will be connected to every other tile in a correct solution, but it may be helpful in the intermediate stages of solving the puzzle.)
Jumble tiles: ‘J’ key
This key turns all tiles that are not locked to random orientations.

(All the actions described below are also available.)

## Net parameters

These parameters are available from the ‘Custom...’ option on the ‘Type’ menu.

Width, Height
Size of grid in tiles.
Walls wrap around
If checked, flow can pass from the left edge to the right edge, and from top to bottom, and vice versa.
Barrier probability
A number between 0.0 and 1.0 controlling whether an immovable barrier is placed between two tiles to prevent flow between them (a higher number gives more barriers). Since barriers are immovable, they act as constraints on the solution (i.e., hints).

The grid generation in Net has been carefully arranged so that the barriers are independent of the rest of the grid. This means that if you note down the random seed used to generate the current puzzle (see below), change the Barrier probability parameter, and then re-enter the same random seed, you should see exactly the same starting grid, with the only change being the number of barriers. So if you're stuck on a particular grid and need a hint, you could start up another instance of Net, set up the same parameters but a higher barrier probability, and enter the game seed from the original Net window.

Ensure unique solution
Normally, Net will make sure that the puzzles it presents have only one solution. Puzzles with ambiguous sections can be more difficult and more subtle, so if you like you can turn off this feature and risk having ambiguous puzzles. (Also, finding all the possible solutions can be an additional challenge for an advanced player.)

## Common actions

These actions are all available from the ‘Game’ menu and via keyboard shortcuts, in addition to any game-specific actions.

(On Mac OS X, to conform with local user interface standards, these actions are situated on the ‘File’ and ‘Edit’ menus instead.)

New game (‘N’, Ctrl+‘N’)
Starts a new game, with a random initial state.
Restart game
Resets the current game to its initial state. (This can be undone.)
Loads a saved game from a file on disk.
Save
Saves the current state of your game to a file on disk.

The Load and Save operations preserve your entire game history (so you can save, reload, and still Undo and Redo things you had done before saving).

Print
Where supported (currently only on Windows), brings up a dialog allowing you to print an arbitrary number of puzzles randomly generated from the current parameters, optionally including the current puzzle. (Only for puzzles which make sense to print, of course – it's hard to think of a sensible printable representation of Fifteen!)
Undo (‘U’, Ctrl+‘Z’, Ctrl+‘_’)
Undoes a single move. (You can undo moves back to the start of the session.)
Redo (‘R’, Ctrl+‘R’)
Redoes a previously undone move.
Copy
Copies the current state of your game to the clipboard in text format, so that you can paste it into (say) an e-mail client or a web message board if you're discussing the game with someone else. (Not all games support this feature.)
Solve
Transforms the puzzle instantly into its solved state. For some games (Cube) this feature is not supported at all because it is of no particular use. For other games (such as Pattern), the solved state can be used to give you information, if you can't see how a solution can exist at all or you want to know where you made a mistake. For still other games (such as Sixteen), automatic solution tells you nothing about how to get to the solution, but it does provide a useful way to get there quickly so that you can experiment with set-piece moves and transformations.

Some games (such as Solo) are capable of solving a game ID you have typed in from elsewhere. Other games (such as Rectangles) cannot solve a game ID they didn't invent themself, but when they did invent the game ID they know what the solution is already. Still other games (Pattern) can solve some external game IDs, but only if they aren't too difficult.

The ‘Solve’ command adds the solved state to the end of the undo chain for the puzzle. In other words, if you want to go back to solving it yourself after seeing the answer, you can just press Undo.

Quit (‘Q’, Ctrl+‘Q’)
Closes the application entirely.

## Specifying games with the game id

There are two ways to save a game specification out of a puzzle and recreate it later, or recreate it in somebody else's copy of the same puzzle.

The ‘Specific’ and ‘Random Seed’ options from the ‘Game’ menu (or the ‘File’ menu, on Mac OS X) each show a piece of text (a ‘game ID’) which is sufficient to reconstruct precisely the same game at a later date.

You can enter either of these pieces of text back into the program (via the same ‘Specific’ or ‘Random Seed’ menu options) at a later point, and it will recreate the same game. You can also use either one as a command line argument (on Windows or Unix); see below for more detail.

The difference between the two forms is that a descriptive game ID is a literal description of the initial state of the game, whereas a random seed is just a piece of arbitrary text which was provided as input to the random number generator used to create the puzzle. This means that:

Descriptive game IDs tend to be longer in many puzzles (although some, such as Cube (sgt-cube(6)), only need very short descriptions). So a random seed is often a quicker way to note down the puzzle you're currently playing, or to tell it to somebody else so they can play the same one as you.
Any text at all is a valid random seed. The automatically generated ones are fifteen-digit numbers, but anything will do; you can type in your full name, or a word you just made up, and a valid puzzle will be generated from it. This provides a way for two or more people to race to complete the same puzzle: you think of a random seed, then everybody types it in at the same time, and nobody has an advantage due to having seen the generated puzzle before anybody else.
It is often possible to convert puzzles from other sources (such as ‘nonograms’ or ‘sudoku’ from newspapers) into descriptive game IDs suitable for use with these programs.
Random seeds are not guaranteed to produce the same result if you use them with a different version of the puzzle program. This is because the generation algorithm might have been improved or modified in later versions of the code, and will therefore produce a different result when given the same sequence of random numbers. Use a descriptive game ID if you aren't sure that it will be used on the same version of the program as yours.

(Use the ‘About’ menu option to find out the version number of the program. Programs with the same version number running on different platforms should still be random-seed compatible.)

A descriptive game ID starts with a piece of text which encodes the parameters of the current game (such as grid size). Then there is a colon, and after that is the description of the game's initial state. A random seed starts with a similar string of parameters, but then it contains a hash sign followed by arbitrary data.

If you enter a descriptive game ID, the program will not be able to show you the random seed which generated it, since it wasn't generated from a random seed. If you enter a random seed, however, the program will be able to show you the descriptive game ID derived from that random seed.

Note that the game parameter strings are not always identical between the two forms. For some games, there will be parameter data provided with the random seed which is not included in the descriptive game ID. This is because that parameter information is only relevant when generating puzzle grids, and is not important when playing them. Thus, for example, the difficulty level in Solo (sgt-solo(6)) is not mentioned in the descriptive game ID.

These additional parameters are also not set permanently if you type in a game ID. For example, suppose you have Solo set to ‘Advanced’ difficulty level, and then a friend wants your help with a ‘Trivial’ puzzle; so the friend reads out a random seed specifying ‘Trivial’ difficulty, and you type it in. The program will generate you the same ‘Trivial’ grid which your friend was having trouble with, but once you have finished playing it, when you ask for a new game it will automatically go back to the ‘Advanced’ difficulty which it was previously set on.

The ‘Type’ menu, if present, may contain a list of preset game settings. Selecting one of these will start a new random game with the parameters specified.

The ‘Type’ menu may also contain a ‘Custom’ option which allows you to fine-tune game parameters. The parameters available are specific to each game and are described in the following sections.

## Specifying game parameters on the command line

(This section does not apply to the Mac OS X version.)

The games in this collection deliberately do not ever save information on to the computer they run on: they have no high score tables and no saved preferences. (This is because I expect at least some people to play them at work, and those people will probably appreciate leaving as little evidence as possible!)

However, if you do want to arrange for one of these games to default to a particular set of parameters, you can specify them on the command line.

The easiest way to do this is to set up the parameters you want using the ‘Type’ menu (see above), and then to select ‘Random Seed’ from the ‘Game’ or ‘File’ menu (see above). The text in the ‘Game ID’ box will be composed of two parts, separated by a hash. The first of these parts represents the game parameters (the size of the playing area, for example, and anything else you set using the ‘Type’ menu).

If you run the game with just that parameter text on the command line, it will start up with the settings you specified.

For example: if you run Cube (see sgt-cube(6)), select ‘Octahedron’ from the ‘Type’ menu, and then go to the game ID selection, you will see a string of the form ‘o2x2#338686542711620’. Take only the part before the hash (‘o2x2’), and start Cube with that text on the command line: ‘sgt-cube o2x2’.

If you copy the entire game ID on to the command line, the game will start up in the specific game that was described. This is occasionally a more convenient way to start a particular game ID than by pasting it into the game ID selection box.

(You could also retrieve the encoded game parameters using the ‘Specific’ menu option instead of ‘Random Seed’, but if you do then some options, such as the difficulty level in Solo, will be missing. See above for more details on this.)

## Unix command-line options

(This section only applies to the Unix port.)

In addition to being able to specify game parameters on the command line (see above), there are various other options:

--game

These options respectively determine whether the command-line argument is treated as specifying game parameters or a save file to load. Only one should be specified. If neither of these options is specified, a guess is made based on the format of the argument.
--generate n
If this option is specified, instead of a puzzle being displayed, a number of descriptive game IDs will be invented and printed on standard output. This is useful for gaining access to the game generation algorithms without necessarily using the frontend.

If game parameters are specified on the command-line, they will be used to generate the game IDs; otherwise a default set of parameters will be used.

The most common use of this option is in conjunction with --print, in which case its behaviour is slightly different; see below.

--print wxh
If this option is specified, instead of a puzzle being displayed, a printed representation of one or more unsolved puzzles is sent to standard output, in PostScript format.

On each page of puzzles, there will be w across and h down. If there are more puzzles than w×h, more than one page will be printed.

If --generate has also been specified, the invented game IDs will be used to generate the printed output. Otherwise, a list of game IDs is expected on standard input (which can be descriptive or random seeds; see above), in the same format produced by --generate.

For example:

```sgt-net --generate 12 --print 2x3 7x7w | lpr
```

will generate two pages of printed Net puzzles (each of which will have a 7×7 wrapping grid), and pipe the output to the lpr command, which on many systems will send them to an actual printer.

There are various other options which affect printing; see below.

--save file-prefix [ --save-suffix file-suffix ]
If this option is specified, instead of a puzzle being displayed, saved-game files for one or more unsolved puzzles are written to files constructed from the supplied prefix and/or suffix.

If --generate has also been specified, the invented game IDs will be used to generate the printed output. Otherwise, a list of game IDs is expected on standard input (which can be descriptive or random seeds; see above), in the same format produced by --generate.

For example:

```sgt-net --generate 12 --save game --save-suffix .sav
```

will generate twelve Net saved-game files with the names game0.sav to game11.sav.

--version
Prints version information about the game, and then quits.

The following options are only meaningful if --print is also specified:

--with-solutions
The set of pages filled with unsolved puzzles will be followed by the solutions to those puzzles.
--scale n
Adjusts how big each puzzle is when printed. Larger numbers make puzzles bigger; the default is 1.0.
--colour
Puzzles will be printed in colour, rather than in black and white (if supported by the puzzle).