private void treeTick(int i) {
        int tree = trees[i];

        // Die
        if (tree >= 100) {
            trees[i] = -1;
            return;
        }

        // Grow
        int shade = 0;
        int[] neighbours = getNeighbours(i);
        for (int nidx : neighbours) {
            int nx = grid.getCellX(nidx),
                ny = grid.getCellY(nidx);
            if (!(grid.isValid(nx,ny) && (grid.isFree(nx,ny) || grid.get(nx,ny) == Tree.COLOR_RGB)))
                continue;
            int neighbour = trees[nidx];
            if (neighbour > tree)
                shade += (neighbour - tree);
        }
        shade = Math.max((int)(shade * (100-tree) * .1),1);
        double chanceToGrow = 1.0 / shade;
        if (TestGame.rand.nextDouble() < chanceToGrow)
            ++trees[i];

        // Multiply
        if (TestGame.rand.nextDouble() < tree * .01) {
            int dx = (TestGame.rand.nextBoolean() ? 1 : -1),
                dy = (TestGame.rand.nextBoolean() ? 1 : -1);
            dx *= Math.pow(TestGame.rand.nextDouble(),3) * 10;
            dy *= Math.pow(TestGame.rand.nextDouble(),3) * 10;

            int newTree = i + dy * grid.getWidth();
            if (!EasyMath.isBetweenOrEqual(grid.getCellX(newTree) + dx,0,grid.getWidth()-1))
                return;
            newTree += dx;
            if (!EasyMath.isBetweenOrEqual(newTree,0,trees.length-1))
                return;
            if (trees[newTree] == -1 && grid.isFree(grid.getCellX(newTree),grid.getCellY(newTree)))
                trees[newTree] = 0;
        }
    }

    private int[] getNeighbours(int i) {
        int i1 = i - grid.getWidth(),
            i2 = i,
            i3 = i + grid.getWidth();
        return new int[]{i1 - 1,i1,i1 + 1,i2 - 1,i2,i2 + 1,i3 - 1,i3,i3 + 1};
    }