Illuminated.js – 2D lights and shadows rendering engine for HTML5 applications(blog.greweb.fr)

    for (var y=y1; y>=y0; --y) {
        var resultY = (0.5+
            (level.topLeft.y - camera.position.y + camera.screen.height / 2 +
            level.cellHeight + y * level.cellHeight-level.cellHeight)
        )|0; // fast clip to int
        for (var x=x1; x>=x0; --x) {
            var tileImageNo = level.layers[z].cells.valueAt([x, y])-1;
            if (tileImageNo==null || tileImageNo<=0) {
                //nothing to do
            } else {
                ctxOnScreenCanvas.drawImage(
                    tiles[tileImageNo],
                    (0.5+
                        (level.topLeft.x - camera.position.x + camera.screen.width / 2 +
                        level.cellWidth + x * level.cellWidth- level.cellWidth)
                    )|0, // fast clip to int
                    resultY
                );
            }
        }
    }