Game of life rules not working properly

Question

I have the following logic code for my Game of Life application in Java. I have the problem that the rules do not act like the default Conway's Game of Life rules. I have read up on them on Wikipedia, and they are the following;

• Any live cell with fewer than two live neighbours dies, as if caused by under-population.
• Any live cell with two or three live neighbours lives on to the next generation.
• Any live cell with more than three live neighbours dies, as if by overcrowding.
• Any dead cell with exactly three live neighbours becomes a live cell, as if by reproduction.

I have attempted to duplicate these rules in the following code, but it acts unlike the normal Conway' Game of Life;

int surroundingLife = 0;
if (lifeMap[cX+1][cY]) { //Right
    surroundingLife++;
}
if (lifeMap[cX-1][cY]) { // Left
    surroundingLife++;
}
if (lifeMap[cX][cY+1]) { // Above
    surroundingLife++;
}
if (lifeMap[cX][cY-1]) { // Below
    surroundingLife++;
}
if (lifeMap[cX-1][cY-1]) { // Bottom left
    surroundingLife++;
}
if (lifeMap[cX+1][cY+1]) { // Top Right
    surroundingLife++;
}
if (lifeMap[cX-1][cY+1]) { // Some other corner (I don't know which one)
    surroundingLife++;
}
if (lifeMap[cX+1][cY-1]) { // Yet another corner (I don't know which one)
    surroundingLife++;
}
if (running) {
    // Logic for life
    if (surroundingLife < 2 && lifeMap[cX][cY]) {// Rule 1. Any live cell with fewer than two live neighbours dies, as if caused by under-population.
        lifeMap[cX][cY] = false;
    } else if (surroundingLife == 2 && lifeMap[cX][cY]) { // Rule 2. Any live cell with two or three live neighbours lives on to the next generation.
        lifeMap[cX][cY] = true;
    } else if (surroundingLife == 3 && lifeMap[cX][cY]) { // Rule 3. Same as above
        lifeMap[cX][cY] = true;
    } else if (surroundingLife > 3 && lifeMap[cX][cY]) { // Rule 4. Any live cell with more than three live neighbours dies, as if by overcrowding.
        lifeMap[cX][cY] = false;
    } else if (surroundingLife == 3 && !lifeMap[cX][cY]) { // Any dead cell with exactly three live neighbours becomes a live cell, as if by reproduction.
        lifeMap[cX][cY] = true;
    }
}   

This is how it looks after running a couple of generations;

It reminds me of the 'maze' ruleset, which is odd.

I don't believe there is a fault with my surroundingLife calculator, as it returns 8 when entities have 8 others surrounding them. Is the problem due to me looping through Y then X?

Answer 1

The problem is that you are modifying the grid in the same pass as you are evaluating what needs to change. Each time you change a cell, you are affecting the outcome of all future tests in the same pass that border that cell.

You need to make a copy of the grid. Always test (read) from that copy, and apply changes (write) to the original.