Drag the green dot (starting point) and red dot (end) where you want, then hit "find path".

The movie will then step through the A* algorithm and you can watch how it chooses the "best" path. Exciting!

In most computer games, the algorithm runs in the background, and once a path is found it just appears on the map or the unit starts moving. Here the algorithm is much slower, so you can watch it at work.

You can select a terrain type at the bottom and draw it onto the board. Trees (green) have a movement penalty of .5, swamps (blue) have a penalty of 2.

You can download the source files for this movie. Go ahead, take a look.

FYI:

• the heuristic distance is being calculated orthogonally (the "Manhattan" distance):
  h = abs(node.x - end.x) + abs(node.y - end.y)
• the open list is implemented as a linked list. This is faster than trying to sort an Array, but probably still slow.
• The initial blocks are generated from a hidden movie clip I drew on with the pencil tool.