Gameplay Programming - Building JavaScript Games for Phones, Tablets, and Desktop - page 216

for (var i = 0; i < 3; i += 1) {
if ((Math.floor(curra / divider) + Math.floor(currb / divider)
+ Math.floor(currc / divider)) % 3 !== 0)
return false;
curra = curra % divider;
currb = currb % divider;
currc = currc % divider;
divider = Math.floor(divider / 3);
}
return true;
First you retrieve the value that represents which jewel you're dealing with, using the variation
member variable of each jewel. Then you define a divider number that is equal to 9 (you first divide
by 9). You next define a for instruction that runs three times. In the body of the for instruction, you
place a condition that the sum of the three variation indices divided by divider should be divisible
by 3. If this isn't the case, you return false because the combination condition doesn't hold for one
of the properties. You assign the rest of the division by the divider to each of the variables containing
the current variation index. You then divide the divider by 3. If you exit the for instruction, it means
in all cases that the condition in the if instruction was true , meaning you found a valid combination.
Because you found a valid combination, you return the value true .
Removing Jewels from the Grid
In the update method, you can now use the isValidCombination method to determine whether a
valid combination exists. For this, you use a while instruction that evaluates all sequences of three
jewels in the middle column:
var middleCol = Math.floor(this._columns / 2);
var i = 0;
while (i < this._rows - 2) {
if (this.isValidCombination(this.at(middleCol, i),
this.at(middleCol, i + 1), this.at(middleCol, i + 2))) {
// do something
}
else
i++;
}
When you find a valid combination, you need to remove these jewels from the grid and insert new
jewels. To do this, you define a method called removeJewel , which removes a jewel from the grid
and inserts a new one. To create a nice “falling down” motion, you place these jewels in different
positions above the grid. You pass the desired y -location as a parameter to the removeJewel method
so it knows where the new jewel should be located. The complete method then becomes
JewelGrid.prototype.removeJewel = function (x, y, newYPosition) {
for (var row = y; row > 0; row -= 1)
this._gameObjects[row * this._columns + x] =
this._gameObjects[(row - 1) * this._columns + x];