A initial plan for how the engine should be formed.

tetwist_marathon.js

var marathon_playfield = new voka.playfield({
  	width: 10,
		height: 20,
		event_handlers: {
			lines_cleared: function(event) {
				var current_level = event.game.level,
					lines_cleared = event.lines_cleared.length;
				var addition = {
					1: current_level * 100,
					2: current_level * 300,
					3: current_level * 500,
					4: current_level * 700
				}[lines_cleared];
				event.game.score += addition;
				event.game.total_lines_cleared += lines_cleared;
				event.game.renderer.popup_lines_cleared(lines_cleared);
				event.game.update_level();
			},
			piece_placed: function(event) {
				if (event.placing_manner === 'spin' &&
					event.placed_piece.type === 't') {
					event.game.score += current_level * 400;
					event.game.renderer.popup_tspin();
				}
			},
			soft_drop: function(event) {
				event.game.score += 2;
			},
			hard_drop: function(event) {
				event.game.score += 20;
			},
			updated: function(event) {
/*				event = {
					previous_matrix: new voka.block_matrix(),
					current_matrix: new voka.block_matrix(),
					type: 'line_cleared',
					lines_cleared: [5,6]
				}*/
				event.game.renderer.render_playfield(this); 
			},
			timer: function(event) {
				switch (event.timer_id) {
				case 'gravity_timer':
					event.playfield.fall();
					break;
				default:
					console.log('unhandled timer.')
				}
			}
		},
		piece_queue: new voka.piece_queue(new voka.standard_tetrinimo_set())
	});

marathon_playfield.register_timer({
	id: 'gravity_timer',
	interval: 1000
});


var marathon = new voka.game({
	playfield: marathon_playfield
});

marathon.level = 1;
marathon.total_lines_cleared = 0;
marathon.update_level = function() {
	if (this.level == 1 && marathon.total_lines_cleared >= 10 ||
		this.level == 2 && marathon.total_lines_cleared >= 30 ||
		this.level == 3 && marathon.total_lines_cleared >= 60 /* ... */) {
		marathon.level += 1;
		this.playfield.update_timer({id: 'gravity_timer',
									 interval: (this.level / 1000) })
		this.renderer.popup_levelup(this.level);
	}
}

function marathon_renderer() {
	// ...
}

marathon.set_renderer(mararthon_renderer);

marathon.start_game();