问HTML 5 Canvas图像渲染

EN

<canvas id="game-viewport" width="760" height="440"></canvas>

<script>

    window.onload = init;

    var map = Array([0,0],[0,0],[0,0],[0,0]);
    var tileSize = 40;

    tileTypes = Array("grass.png");
    tileImage = new Array();

    var loaded = 0;
    var loadTimer;

    function loadImage(){
        for(i = 0; i < tileTypes.length; i++){
            tileImage[i] = new Image();
            tileImage[i].src = "./game/lib/icons/own_icons/" + tileTypes[i];
            tileImage[i].onload = function(){
                loaded++;
            }
        }
    }

    function loadAll(){
        if(loaded == tileTypes.length){
            clearInterval(loadTimer);
            drawMap();
        }
    }

    function drawMap(){
        var mapX = 80;
        var mapY = 10;

        for(i = 0; i < map.length; i++){
            for(j = 0; j < map[i].length; j++){
                var drawTile = map[i][j];
                var xPos = (i - j) * tileSize;
                var yPos = (i + j) * tileSize;
                ctx.drawImage(tileImage[drawTile], xPos, yPos);
            }
        }
    }

    function init(){
        var canvas = document.getElementById('game-viewport')
        var ctx = canvas.getContext('2d');
        loadImage();
        loadTimer = setInterval(loadAll, 100);
    }

</script>