CODEWITHSUNDEEP
c#arraysmath
Tomáš Zato
Tomáš Zato

Reputation: 53139

How to map 8 directions to 1D array

I have 8 cursors for 8 directions on screen.

directions on screen

I want to put them into array and chose them depending on direction vector. The order does not matter, but I need to assign i coordinate in 1D array for every vector seen above. I spend a long time trying to invent the formula for it, but nothing would work.

The values in vector can be 0,1,-1.

Pseudo code:

Cursor getCursor(int x, int y) {
    int i = TheFunctionINeed(x,y);
    return cursors[i];
}

Note: Because so many guys were confused by what do I want, I used the answer to make following fiddle: Mapping vectors to array.

Upvotes: 3

Views: 2930

Answers (6)

Ananda G
Ananda G

Reputation: 2539

I have a easiest way to map this. Simply define your array like this

ax8 = [-1,-1,0,1,1,0,-1,1,-1]

Now loop through till 8, it will give all the points

for i in range(8):
    print(ax8[i], ax8[i+1])

It will rotate clockwise and pick the coordinates one by one. Hope this helps!

Upvotes: 1

Sinatr
Sinatr

Reputation: 21999

To map (x,y) as 1d array people uses common formula

index = x + y * (xmax + 1)

Let's try to do same for (x,y,z), taking in account what all values are in range [-1;1] (can have one of tree values: -1, 0 or 1).

First only for (x,y), note, you need offset to avoid negative indexes

xy = (x + 1) + (y + 1) * 3

Now mapping (xy; z), note that xymax value is 8

xyz = xy + (z + 1) * 9

Which makes final formula

index = (x + 1) + (y + 1) * 3 + (z + 1) * 9.

Testing:

vector       index
------------------
(-1,-1,-1)   0
(0,0,0)      13
(1,1,1)      27

Upvotes: 3

Fleve
Fleve

Reputation: 401

I would also add 0,0 to make the calculation easier.

The function you need, let's call it "GetCursorIndex", can work like this:

int getCursorIndex(int x, int y)
{
    return (x+1)+(y+1)*3;
}

If you have your Cursors sorted, so that the first represents -1, -1 and the last one 1, 1 you can add a the one for -1, 0 or 1, 0 in in the central Position of the Array, twice... or you can create a Cursor for the Position 0,0... maybe it makes sense.

Upvotes: 2

juharr
juharr

Reputation: 32266

Another option would be to use Dictionary<Tuple<int,int>,Cursor>.

var cursors = new Dictionary<Tuple<int,int>, Cursor>();
cursors.Add(new Tuple<int,int>(-1,-1), someCursorHere);
// continue filling it in for each vector.

Cursor getCursor(int x, int y) 
{
    Cursor c;
    if(cursors.TryGetValue(new Tuple<int,int>(x,y), out c)
        return c;
    // throw an exception here or return a default value?
}

Upvotes: 1

thatzacdavis
thatzacdavis

Reputation: 26

You could arbitrarily start at a spot such as the upper left corner and order them going around clockwise.

So: [-1,-1] = 0, [-1,0] = 1, etc.

Upvotes: -1

Hamid Pourjam
Hamid Pourjam

Reputation: 20754

it contains 9 elements, I have added (0, 0) for simplicity.

a = {(-1, -1),  (-1, 0),  (-1, 1),  (0, -1),  (0, 0),  (0, 1),  (1, -1),  (1, 0),  (1, 1)}


ZeroBasedIndex(x, y) = (x + 1) * 3 + (y + 1)

Upvotes: 5

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