access a cell in a 2d Array grid

Programming Questions

sanspot

access a cell in a 2d Array grid

in Programming Questions • 1 year ago

Hey everybody...

I'm a bit at loss at the moment... I'm not an expert coder so I'm still learning to use basic things such as how to deal with 2d Array...
What I'm trying to do is, I guess, not that hard. I created a grid of objects with the line of code provided on the explanation of a 2dimensional array... like this;

Tile [][] grid;

//number of rows and columns

int cols;

int rows;

void setup() {

size(600, 600);

cols=width/6;

rows=height/6;

grid = new Tile[cols][rows]; //the array dimensions are equal to n.of rows/columns

//loop through cols and rows

for (int i=0; i<cols; i++) {

for (int j=0; j<rows; j++) {

//initiate objects

grid[i][j] = new Tile (i*60, j*60, 60, 200);

}

}

}

SO this part I get, it's not complicated... What I want to do next somehow gets me confused. What I did is first rendering the grid with a fill(200).
I then wanted to change the color of one of the cell, meaning I have to access it by specifying the indexes of the array, something like this

void draw() {
background(50);
for (int i=0; i<cols; i++) {
for (int j=0; j<rows; j++) {
//show me them goodies
grid[i][j].display();
}
}
grid[4][4].black();
}

So the nested loops actually render the grid (display is a class method), and the line 10 should access the Tile at position 4,4 and change fill(200) to 0....

but it doesn't... any idea why?

I'll write you down also the class file (just in case);

class Tile {
float x, y;
float side;
int col;
Tile (float tempX, float tempY, float tempSide, int tempCol) {
x = tempX;
y = tempY;
side = tempSide;
col = tempCol;
}
void display() {
rect (x, y, side, side);
stroke(220);
fill(col);
}
void black() {
stroke(220);
fill(0);
}
}

thanks in advance

Replies(10)

sanspot

Re: access a cell in a 2d Array grid

1 year ago

as a side note: I've been looking around and in similar cases people suggested to use an ArrayList....

I'm trying to create a template for cellular automata, Stephen Wolfram style if you know him ( http://mathworld.wolfram.com/CellularAutomaton.html) , so i thought creating a grid of Objs and being able to turn them on and off would make the case, hence the 2d Array...

I'm open to suggestions in case You might think there is an easier solution...

Chrisir

Re: access a cell in a 2d Array grid

1 year ago

In the method display:

void display() {
rect (x, y, side, side);
stroke(220);
fill(col);
}

better

void display() {
stroke(220);
fill(col);
rect (x, y, side, side);
}

Since you set the color with fill and you want to have that color for the rect you have to set the color before drawing the rect.

The method black() is wrong:

void black() {
stroke(220);
fill(0);
}

since the property col is used in the method display(), you have to change this property in the method black:

void black() {
col = color (0) ;
}

That is permanent whereas

stroke(220);
fill(0);

would only be temporarily.

(not tested)

Greetings, Chrisir

P.S.
Since you know how many cells you have, ArrayList is not needed.
I think a 2D Array is the right approach for an cellular automata (CA).
There are a few in the learning section, in the forum or on
http://www.openprocessing.org I think.

sanspot

Re: Re: access a cell in a 2d Array grid

1 year ago

ok it works!

I'll take the chance to see if I understand why... With the line of code you provided I change the property of the obj in position [4][4] right? makes sense...
But how come my line of code doesn't it? I mean what I thought I was doing is access the object in that position and simply refill it with an new color...

The weird thing that threw me off is that my code did change the color, but always and only of the first obj in position [0][0]... that is why I thought it was a problem of index, not of property control...
Is it because I was only telling it to change a fill without referencing to a specific obj? meaning that it displayed the fill(0) but didn't know where to place it (so it just ended up in [0][0])?

hope I make sense

Chrisir

Re: access a cell in a 2d Array grid

1 year ago

With the line of code you provided I change the property of the obj in position [4][4] right? makes sense...

yes, with

void black() {
col = color (0) ;
}

I do this.

This:

But how come my line of code doesn't it? I mean what I thought I was doing is access the object in that position and simply refill it with an new color...

is referring to

void black() {
stroke(220);
fill(0);
}

with those lines you don't influence your objects or arrays at all.
You only influence the next drawing action (e.g. rect) that takes place.
This is probably important to understand. To change the properties of your
object you have to access it via those properties like col = color (0) ;
then you read it out and use it with fill. The command fill then determines what color the next rect has:
fill(col);

Since draw() runs approx. 60 times a second and you executed

grid[4][4].black();

at the end of draw() each time, it might have influenced the display of grid[0][0] (the rect) since it was
at the beginning of draw() when it run the next time (and you had

stroke(220);
fill(col);

after rect() in the method display() ).

Greetings, Chrisir

bporter88

Re: access a cell in a 2d Array grid

8 months ago

In this script, how do you change the number of cells in the grid?

Chrisir

Re: access a cell in a 2d Array grid

8 months ago

this lines:

cols=width/6;

rows=height/6;

grid = new Tile[cols][rows]; //the array dimensions are equal to n.of rows/columns

do this

so you can either change the width and height in the line size()
or change the two 6 you have

sanspot

Re: access a cell in a 2d Array grid

8 months ago

Hi Porter

If you want to have more squares on screen with the size they have now, what you can do is play around with size(). The numbers of cols and rows is related to that, so changing the number in size will show you more rows or columns. Bear in mind that the line

grid[i][j] = new Tile (i*60, j*60, 60, 200);

will define how big the squares are. So if you keep the code as it is simply changing the square size to 10 like this

grid[i][j] = new Tile (i*10, j*10, 10, 200);

will make them way smaller (and you end up with more rows and cols).
Hope this helps

sanspot

Re: access a cell in a 2d Array grid

8 months ago

By the way I have a more updated version somewhere on my computer at home. I see if I can post it here. It was a bit better than this one!

bporter88

Re: access a cell in a 2d Array grid

8 months ago

sanspot,

YOU THE MAN! thanks for the help!

sanspot

Re: Re: access a cell in a 2d Array grid

7 months ago

Porter

I forgot to post this for you:

Tile [] grid;
int unit = 8;
int count;
void setup() {
size(96, 64);
noStroke();
background(255);
int wideCount = width / unit; //12 (6+6)
int highCount = height / unit; //8
count = wideCount * highCount;
grid = new Tile[count];
int index = 0;
for (int x=0; x< wideCount; x++) {
for (int y=0; y< highCount; y++) {
//start creating objects
grid[index++] = new Tile (x*unit, y*unit, unit);
}
}
index = 0;
for (int x=0; x< wideCount; x++) {
for (int y=0; y< highCount; y++) {
grid[index++].display();
}
}
}
void draw() {
}

and the class

class Tile {
float x, y;
float side;
int col;
int chance;
Tile (float tempX, float tempY, float tempSide) {
x = tempX;
y = tempY;
side = tempSide;
float fate = random(2);
chance = int(fate * 1.4);
}
void display() {
fill(chance<=1?0:255);
rect (x, y, side, side);
//rect (x, 9*rows-y+3, side, side);
rect (11*unit-x, y, side, side); //right
//rect (x+60, y, side, side); //right without flipping
}
}

Top Reply