Viewport and Culling on a Tile Map

Code showing modifications

<!DOCTYPE html>
<html>
<head>

<script type="text/javascript">
var ctx = null;
var gameMap = [
	0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
	0, 1, 1, 1, 0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, 1, 1, 1, 0,
	0, 1, 0, 0, 0, 1, 0, 0, 0, 0, 1, 1, 1, 0, 1, 0, 1, 0, 0, 0,
	0, 1, 1, 1, 1, 1, 1, 1, 1, 0, 1, 1, 1, 0, 1, 1, 1, 1, 1, 0,
	0, 1, 0, 1, 0, 0, 0, 1, 1, 0, 1, 1, 1, 0, 1, 0, 1, 1, 1, 0,
	0, 1, 0, 1, 0, 1, 0, 0, 1, 0, 1, 1, 1, 1, 1, 0, 1, 1, 1, 0,
	0, 1, 1, 1, 1, 1, 1, 1, 1, 0, 1, 1, 1, 1, 1, 0, 0, 1, 0, 0,
	0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, 0, 0, 1, 0, 1, 1, 1, 0,
	0, 1, 1, 1, 0, 1, 1, 1, 1, 1, 1, 0, 1, 1, 1, 1, 1, 1, 1, 0,
	0, 0, 1, 0, 0, 1, 0, 0, 1, 0, 1, 1, 1, 1, 1, 1, 0, 1, 1, 0,
	0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, 1, 1, 0,
	0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, 0, 1, 0,
	0, 1, 0, 0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0,
	0, 1, 0, 1, 1, 1, 1, 1, 0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0,
	0, 1, 0, 1, 0, 0, 0, 1, 0, 1, 1, 1, 1, 1, 1, 1, 0, 1, 1, 0,
	0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 0, 0, 0, 1, 1, 0, 0, 0, 0,
	0, 1, 0, 1, 1, 1, 0, 1, 0, 1, 1, 1, 1, 0, 1, 1, 1, 0, 1, 0,
	0, 1, 0, 0, 0, 0, 0, 1, 0, 1, 0, 0, 1, 0, 1, 1, 1, 0, 1, 0,
	0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0,
	0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0
];
var tileW = 40, tileH = 40;
var mapW = 20, mapH = 20;
var currentSecond = 0, frameCount = 0, framesLastSecond = 0, lastFrameTime = 0;

var keysDown = {
	37 : false,
	38 : false,
	39 : false,
	40 : false
};

var viewport = {
	screen		: [0,0],
	startTile	: [0,0],
	endTile		: [0,0],
	offset		: [0,0],
	update		: function(px, py) {
		this.offset[0] = Math.floor((this.screen[0]/2) - px);
		this.offset[1] = Math.floor((this.screen[1]/2) - py);

		var tile = [ Math.floor(px/tileW), Math.floor(py/tileH) ];

		this.startTile[0] = tile[0] - 1 - Math.ceil((this.screen[0]/2) / tileW);
		this.startTile[1] = tile[1] - 1 - Math.ceil((this.screen[1]/2) / tileH);

		if(this.startTile[0] < 0) { this.startTile[0] = 0; }
		if(this.startTile[1] < 0) { this.startTile[1] = 0; }

		this.endTile[0] = tile[0] + 1 + Math.ceil((this.screen[0]/2) / tileW);
		this.endTile[1] = tile[1] + 1 + Math.ceil((this.screen[1]/2) / tileH);

		if(this.endTile[0] >= mapW) { this.endTile[0] = mapW-1; }
		if(this.endTile[1] >= mapH) { this.endTile[1] = mapH-1; }
	}
};

var player = new Character();

function Character()
{
	this.tileFrom	= [1,1];
	this.tileTo		= [1,1];
	this.timeMoved	= 0;
	this.dimensions	= [30,30];
	this.position	= [45,45];
	this.delayMove	= 700;
}
Character.prototype.placeAt = function(x, y)
{
	this.tileFrom	= [x,y];
	this.tileTo		= [x,y];
	this.position	= [((tileW*x)+((tileW-this.dimensions[0])/2)),
		((tileH*y)+((tileH-this.dimensions[1])/2))];
};
Character.prototype.processMovement = function(t)
{
	if(this.tileFrom[0]==this.tileTo[0] && this.tileFrom[1]==this.tileTo[1]) { return false; }

	if((t-this.timeMoved)>=this.delayMove)
	{
		this.placeAt(this.tileTo[0], this.tileTo[1]);
	}
	else
	{
		this.position[0] = (this.tileFrom[0] * tileW) + ((tileW-this.dimensions[0])/2);
		this.position[1] = (this.tileFrom[1] * tileH) + ((tileH-this.dimensions[1])/2);

		if(this.tileTo[0] != this.tileFrom[0])
		{
			var diff = (tileW / this.delayMove) * (t-this.timeMoved);
			this.position[0]+= (this.tileTo[0]<this.tileFrom[0] ? 0 - diff : diff);
		}
		if(this.tileTo[1] != this.tileFrom[1])
		{
			var diff = (tileH / this.delayMove) * (t-this.timeMoved);
			this.position[1]+= (this.tileTo[1]<this.tileFrom[1] ? 0 - diff : diff);
		}

		this.position[0] = Math.round(this.position[0]);
		this.position[1] = Math.round(this.position[1]);
	}

	return true;
}

function toIndex(x, y)
{
	return((y * mapW) + x);
}

window.onload = function()
{
	ctx = document.getElementById('game').getContext("2d");
	requestAnimationFrame(drawGame);
	ctx.font = "bold 10pt sans-serif";

	window.addEventListener("keydown", function(e) {
		if(e.keyCode>=37 && e.keyCode<=40) { keysDown[e.keyCode] = true; }
	});
	window.addEventListener("keyup", function(e) {
		if(e.keyCode>=37 && e.keyCode<=40) { keysDown[e.keyCode] = false; }
	});

	viewport.screen = [document.getElementById('game').width,
		document.getElementById('game').height];
};

function drawGame()
{
	if(ctx==null) { return; }

	var currentFrameTime = Date.now();
	var timeElapsed = currentFrameTime - lastFrameTime;

	var sec = Math.floor(Date.now()/1000);
	if(sec!=currentSecond)
	{
		currentSecond = sec;
		framesLastSecond = frameCount;
		frameCount = 1;
	}
	else { frameCount++; }

	if(!player.processMovement(currentFrameTime))
	{
		if(keysDown[38] && player.tileFrom[1]>0 && gameMap[toIndex(player.tileFrom[0], player.tileFrom[1]-1)]==1) { player.tileTo[1]-= 1; }
		else if(keysDown[40] && player.tileFrom[1]<(mapH-1) && gameMap[toIndex(player.tileFrom[0], player.tileFrom[1]+1)]==1) { player.tileTo[1]+= 1; }
		else if(keysDown[37] && player.tileFrom[0]>0 && gameMap[toIndex(player.tileFrom[0]-1, player.tileFrom[1])]==1) { player.tileTo[0]-= 1; }
		else if(keysDown[39] && player.tileFrom[0]<(mapW-1) && gameMap[toIndex(player.tileFrom[0]+1, player.tileFrom[1])]==1) { player.tileTo[0]+= 1; }

		if(player.tileFrom[0]!=player.tileTo[0] || player.tileFrom[1]!=player.tileTo[1])
		{ player.timeMoved = currentFrameTime; }
	}

	viewport.update(player.position[0] + (player.dimensions[0]/2),
		player.position[1] + (player.dimensions[1]/2));

	ctx.fillStyle = "#000000";
	ctx.fillRect(0, 0, viewport.screen[0], viewport.screen[1]);

	for(var y = viewport.startTile[1]; y <= viewport.endTile[1]; ++y)
	{
		for(var x = viewport.startTile[0]; x <= viewport.endTile[0]; ++x)
		{
			switch(gameMap[((y*mapW)+x)])
			{
				case 0:
					ctx.fillStyle = "#685b48";
					break;
				default:
					ctx.fillStyle = "#5aa457";
			}

			ctx.fillRect( viewport.offset[0] + (x*tileW), viewport.offset[1] + (y*tileH),
				tileW, tileH);
		}
	}

	ctx.fillStyle = "#0000ff";
	ctx.fillRect(viewport.offset[0] + player.position[0], viewport.offset[1] + player.position[1],
		player.dimensions[0], player.dimensions[1]);

	ctx.fillStyle = "#ff0000";
	ctx.fillText("FPS: " + framesLastSecond, 10, 20);

	lastFrameTime = currentFrameTime;
	requestAnimationFrame(drawGame);
}
</script>

</head>
<body>

<canvas id="game" width="400" height="400"></canvas>

</body>
</html>

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