Progress on the NIM game has gone well and we have the core components of the game implemented (see the earlier sections previously posted). While
we now have the core game mechanics implemented, we do not have a
game. Right now we just have the ability for the player to take gems
unitl there are no more gems. To have a proper game we need to be
able to alternate between two players (the human and the computer).
We also want the user interface to not accept input while the game is
animating or the computer is playing. For this we will need to know
what the movie is doing at any point of time. The easiest way of
tracking this is to have a gamestate variable that holds the current
state of the game with constants defined for the four states that we
are concerned with.
//
explain the different states of the game
var
GAMESTATE_PLAYER_PLAYING = 1;
var
GAMESTATE_PLAYER_ANIMATING = 2;
var
GAMESTATE_COMPUTER_PLAYING = 3;
var
GAMESTATE_COMPUTER_ANIMATING = 4;
var
gamestate = GAMESTATE_PLAYER_PLAYING;
This
means that we can now update the button handling routines to make
sure that it is the player’s turn before doing anything with the
button click. The new code is bolded.
function
handleOneButton(e) {
if
(gamestate != GAMESTATE_PLAYER_PLAYING)
return;
--gemsRemaining;
gamestate
= GAMESTATE_PLAYER_ANIMATING;
gameMovie.play();
}
function
handleTwoButton(e) {
if
(gamestate != GAMESTATE_PLAYER_PLAYING)
return;
gemsRemaining
-= 2;
gamestate
= GAMESTATE_PLAYER_ANIMATING;
gameMovie.play();
}
function
handleThreeButton(e) {
if
(gamestate != GAMESTATE_PLAYER_PLAYING)
return;
gemsRemaining
-= 3;
gamestate
= GAMESTATE_PLAYER_ANIMATING;
gameMovie.play();
}
The
gem removal routine can also be fixed up to nearly it’s final form
by having it start the computer’s turn after the player’s turn
has finished being animated and returning to the control to the
player once the computer has finished it’s turn.
function
gemRemoved(gemCount) {
if
(gemCount <= gemsRemaining) {
gameMovie.stop();
if
(gamestate == GAMESTATE_PLAYER_ANIMATING)
computerTurn();
else
{
gamestate
= GAMESTATE_PLAYER_PLAYING;
}
}
}
Of
course, for there to be a computer player, the computer needs to know
how to play the game. It is quite possible to have the computer play
the game perfectly, but that is not much fun for the player so
instead the computer will play randomly until near the end of the
game where they will take the opportunity to win the game if it
presents itself.
function
computerTurn() {
if
(gemsRemaining <= 3) {
gemsRemaining
= 0;
setMessage("Computer
taking " + gemsRemaining);
}
else {
var
numToPick = Math.floor(Math.random() * 3) + 1;
setMessage("Computer
taking " + numToPick);
gemsRemaining
-= numToPick;
}
Random
number are technically not random, but are pseudo-random but the
details is not important. What had to be understood is that the
Math.random() function returns a number between 0 and up to but not
including 1 so that number needs to be adjusted to a usable value.
Multiplying by three gives us a random number between 0 and just
under 3. We want a decimal number so we use the Math.floor function
to round the number down giving us a number between 0 and 2. Add one
to this and we have the number in the desired range.
This
leaves us with one final issue, which is winning or losing the game. This will be covered next fortnight!
