cell_y && y < cell_y + cell_height)
				floating_cell_bits[i] = 1 - floating_cell_bits[i];
		}
		floating_draw();
	}, false);
}

function floating_draw() {
	var floating = document.getElementById("floating");
	var floating_context = floating.getContext("2d");

	// background
	floating_context.fillStyle="#dbd5a0";
	floating_context.fillRect(0, 0, w, h);
	
	// cells
	for(var i = 0; i < floating_cell_xs.length; ++i) {
		floating_context.fillStyle = floating_cell_colors[i];
		floating_context.fillRect(floating_