Gameplay Programming - Learning C# by Programming Games - page 237

First, we retrieve the value that represents which jewel we are dealing with, using
the Variation property. Then we define a divider number that is equal to 9 (we are
first going to divide by 9). We then define a for -instruction that runs three times. In
the body of the for -instruction, we place a condition that the sum of the three vari-
ation indices divided by divider should be divisible by 3. If this is not the case, we
return false since the combination condition does not hold for one of the properties.
We then assign the rest of the division by the divider to each of the variables con-
taining the current variation index. We then divide the divider by 3. If we exit the
for -instruction, it means that in all cases, the condition in the if -instruction was true ,
meaning that we found a valid combination. Since we found a valid combination,
we return the value true .

16.4.3 Removing Jewels from the Grid

Inside the HandleInput method, we can now use the IsValidCombination method to de-
termine if a valid combination exists. For this, we use a while -instruction that evalu-
ates all sequences of three symbols in the middle column:

int middleCol = this .Columns / 2;
int i=0;
while (i < this .Rows − 2)

{

if (IsValidCombination((Jewel)grid[middleCol, i],
(Jewel)grid[middleCol, i + 1],
(Jewel)grid[middleCol, i + 2]))

{

dosomething...

}
else
i++;

}

When we find a valid combination, we need to remove these jewels from the grid,
and insert new jewels. For this, we define a method called ReplaceJewel , which re-
moves a jewel from the grid, and inserts a new one. Because we want to create a nice
'falling down' motion, we place these jewels in different positions above the grid.
We pass the desired y -location as a parameter to the ReplaceJewel method so that it
knows where the new jewel should be located. The complete method then becomes

public void ReplaceJewel( int x, int y, int newYPosition)
{

this .Clear(x, y);
Jewel s = new Jewel();
this .Add(s);
s.Position = new Vector2(x ∗ cellWidth, newYPosition);

}