Problem: mapping mouse co-ordinates to a list of nodes in a graph.

Question

Hi.
I have an undirected graph containing many nodes, some represent squares/tiles and some represent rooms in a board-game called Cluedo.
Each node has an ID: -
Rooms are called by the room name. -> Kitchen/Lounge
Squares are called by the concatenated x/y position. -> A1/A2/K20
I have created an algorithm to find the shortest path between two nodes in the graph.
The problem I'm faced with is finding a way to map co-ordinates on the image file to these IDs. I have seen an implementation of a similar idea with an invisible image acting as a "colour-mask", so when the click hits the graphical map a function works out the colour of that pixel on the "colour-mask" and then uses a look-up table to find out which ID that is associated to.
The problem with the above is that a Cluedo board has about 22x22 tiles and several rooms (each room would occupy several tiles in an undefined shape.)
I've provided two example map files:
http://www.dcs.qmul.ac.uk/~ade1/map.gif
http://www.dcs.qmul.ac.uk/~ade1/map2.gif
Does anyone have a suggestion of how I could solve this problem using what's available to me with Java?
I'd appreciate any suggestions,
Alexander Ellis

Answer 1

Create a two-dimensional array that maps from grid coordinates to node/room objects.
NodeOrRoom[][] grid = new NodeOrRoom[22][22];
grid[0][0] = kitchen;
grid[1][0] = kitchen;
nodeLookup(int pixelTop, int pixelLeft) {
  return grid[pixelTop / gridCellHeight][pixelLeft / gridCellWidth];
}Matthew