Crosspix

It's funny. When you're at school, you barely register grids and numbers. You have a dim notion that they're somehow involved in mathematics, possibly geography, but they're approximately as relevant to you as long division, the water table, and the word 'conjugate'.

Then, a few years later, somebody leaves a sudoku puzzle half-finished on a train, you take a look, trace your finger along the lines, a little bell rings, and suddenly you can't get enough.

Crosspix – a game popularised by Picross on the DS and entitled Tsunami in its paper form – is what mathematics should have been like at school, and a more accessible answer to sudoku.

For those who don't know, it works like this: You have a blank grid of, say, 10x10 squares. As in Minesweeper, the squares either conceal something or they don't, and it's your task to work out which are which using the numbers the game sparingly supplies.

Whereas Minesweeper places these numbers within the board, however, Crosspix lines them up outside it, above and to the left of each column and row, so that if 4, 6, 2 is provided beside a row there will be a line of four, then six, then two filled squares, in that order, each separated by at least one unfilled square.

If the grid is ten across and the number given is 10, easy. You just fill in every square in that line. If the 10 fills a row, then you know where at least one of the squares in each of the perpendicular columns that make it up belongs, and from those you can usually deduce the locations of a few more filled squares. And so on until you've got yourself a picture.

There have been several serviceable versions of this game on mobile already, including the excellent PicoPix, so what is Glu bringing to the party?

In terms of gameplay, nothing new. In terms of presentation and depth, however, Crosspix is comfortably ahead of its competition in this credibly populated puzzle sub-genre, thanks to its simple but effective setting.

It all takes place in the Crosspix Museum, of which you are the new owner. Your mission is to steer your white-haired avatar from room to room uncovering pictures with your mathematical prowess, which many not sound like a big deal, but it brings a lot a character to a game with very few cracks into which character might conceivably be stuffed.

Each of the rooms is themed, so that the Clothing exhibit contains a picture of a shoe, a hat, a pair of boxer shorts, while the much more difficult Animals room contains pictures of an ostrich, a dog, and so on. You get the idea.

Although these objects are sometimes obscure, represented as they are by a few filled blocks, once you solve each puzzle they acquire a few colours and look, though not always completely clear, quite pretty, like impressions in stained glass.

The puzzles grow more difficult as you make your way towards the back of the gallery, and right at the back they're very tough indeed, just as they're trivially easy in the rooms near the entrance. There are 12 such rooms, each containing ten puzzles, as well as a further four 'Super Crosspix' rooms, each of which contains nine expert-level grids. That all adds up to more than 150 grids, on top of which you can also create and store up to ten of your own.

In terms of numbers and presentation, then, Crosspix competes with any book of Tsunami puzzles you might hope to buy for the same kind of price as you can download this game. There is one respect, however, in which it arguably compares poorly with the traditional pen-and-paper versions.

Rather than allowing you to get hopelessly entangled in the ramifications of an error, Crosspix gives you lives, removing one every time you try to fill in a square that shouldn't be filled. While this undoubtedly forestalls one kind of frustration, it also removes a dimension of the original's gameplay, which will either appeal to you or not depending on your orientation.

In any case, it's a small point, and one to which you shouldn't pay the slightest bit of attention if grids and numbers are your thing.