Code Sketch

size(600, 600)
cleari()
setBackground(white)
originBottomLeft()

val tileCount = 3
val tileWidth = cwidth / tileCount
val tileHeight = cheight / tileCount

def shape(w: Double, h: Double) = {
    val len = math.min(w, h) * 3 / 4
    picStackCentered(noPen -> Picture.rectangle(w, h), Picture.ellipseInRect(len, len))
}

case class Block(x: Double, y: Double, w: Double, h: Double, c: Color)
var blocks = ArrayBuffer.empty[Block]

def drawBlock(b: Block) {
    val pic = shape(b.w, b.h)
    pic.setPosition(b.x, b.y)
    val d = mathx.distance(b.x, b.y, mouseX, mouseY)
    val f = mathx.map(d, 0, 800, 0.3, .9)
    val angle = mathx.angle(b.x, b.y, mouseX, mouseY)
    pic.setPenColor(b.c)
//    pic.setFillColor(b.c.fadeOut(f))
    pic.setPenThickness(2)
    draw(pic)
}

def splitSomeBlocks(blocks: ArrayBuffer[Block], p: Double): ArrayBuffer[Block] = {
    val blocks2 = ArrayBuffer.empty[Block]
    repeatFor(blocks) { b =>
        if (randomDouble(1) < p) {
            val newBlocks = Array(
                Block(b.x, b.y, b.w / 2, b.h / 2, randomColor),
                Block(b.x, b.y + b.h / 2, b.w / 2, b.h / 2, randomColor),
                Block(b.x + b.w / 2, b.y, b.w / 2, b.h / 2, randomColor),
                Block(b.x + b.w / 2, b.y + b.h / 2, b.w / 2, b.h / 2, randomColor)
            )
            blocks2.appendAll(newBlocks)
        }
        else {
            blocks2.append(b)
        }
    }
    blocks2
}

setup {
    repeatFor(rangeTill(0, cheight, tileHeight)) { posY =>
        repeatFor(rangeTill(0, cwidth, tileWidth)) { posX =>
            val block = Block(posX, posY, tileWidth, tileHeight, randomColor)
            blocks.append(block)
        }
    }
    repeat(5) {
        blocks = splitSomeBlocks(blocks, 0.3)
    }
}

drawLoop {
    erasePictures()
    repeatFor(blocks) { b =>
        drawBlock(b)
    }
}