!Abut

 
Martin Hansen
 

This issue of RISCOScode is going to tap into the surge of interest in puzzles from the early days of computing. One puzzle enjoying a renaissance is the "15" sliding tile puzzle. Eight versions of this amusement, for example, are on sale in Apple's iPhone App store. Typically they cost a few pence to buy.
 
The traditional version of the puzzle has numbers printed on the tiles. A tougher challenge replaces the numbers with parts of a picture. You know you have solved the puzzle when the picture is revealed.
 

I decided to write an up-to-date version of the "15" puzzle for the RISC OS desktop. I thought it would make a popular free release on RISCOScode. The result is some new RISC OS software called Abut. It comes with eleven sets of tiles. Ten of these are shown running down the right hand side of this page. The eleventh is the default set with numbers on. In the next issue of RISCOScode, I'll show how to turn a photograph of your own into a set of tiles for dragging and dropping into Abut.
 
I became interested in the "15" passtime when I read a short account of a general strategy for solving it. What I liked was that the strategy was in the form of general guidelines. I still had to do some thinking.
 
It's easiest to explain the strategy with the default set of number tiles. The top left diagram below shows a typical starting mix-up and top right is the puzzle solved, with the numbers in order. Now that you know what we're trying to achieve, let's begin. Bottom left is the first step - get the numbers 1, 4, 13 and 15 into the corner positions shown. I've blanked all other numbers as they can be anything at this stage. Bottom right is the second step, with the numbers 14 and 11 in position.
 

Now focus on the edges. Below, left, the top edge is done. Below, right, another edge is completed. Next get the 8 and 12 into the remaining edge position. Having got that far I figure you'll be able to finish it.
 

 
DOWNLOAD ABUT (2MB zip file)
 

This is RISC OS software. To run this software on Microsoft, Apple or Linux operating systems will require an emulator such as that sold by Virtual Acorn.

Click on the icon above to download Abut and sets of picture tiles.
 
Many thanks to photographer Guy Holmes for the three wildlife photographs, all taken in Zanzibar. Chris Williams managed to track down an ArtWorks version the classic 'drobe' rocket, which for a while we feared lost. The geometric design is an ArtGraph image - a future version of ArtGraph will feature a "Save as an Abut file" option. The 'fire bat' is from Digital Blasphemy.