let grid = 5;

// You can find the Turtle API reference here: https://turtletoy.net/syntax
var fullOpacity = 100

Canvas.setpenopacity(1 / fullOpacity);

var size = 200 / grid;

// Global code will be evaluated once.
const bales = [];
for(var j = 0; j < grid * grid; j++) {
    bales[j] = [];
    for(var i = 0; i < getBaleSize(j); i++) {
        bales[j][i] = new Turtle();
        bales[j][i].penup();
        bales[j][i].goto(
              ((((j % grid) + .5)     * size) - 100) - (75 / grid)
            , ((((j / grid | 0) + .5) * size) - 100) - (20 / grid)
        )
        bales[j][i].pendown();
    }
}

// The walk function will be called until it returns false.
function walk(i) {
    for(var k = 0; k < bales.length; k++) {
        for(var j = 0; j < bales[k].length; j++) {
            bales[k][j].forward(150 / grid);
            bales[k][j].right(144);
        }
    }
    return i < 4;
}

function getBaleSize(j) {
    var max = grid * grid;
    return fullOpacity * (Math.cos( Math.PI + ((j / max) * (Math.PI / 2)) ) + 1);
}