HTML5 の Canvas でテキストの折り返し

canvas_newline.js

var canvasWidthPx = 640;
var text = "sample text sample text sample text sample text";
var textWidthPx = context.measureText(text).width;
var charWidthPx = Math.ceil(textWidthPx / text.length);
var nWordInLine = Math.floor(canvasWidthPx / charWidthPx);
var nLine = Math.ceil(text.length / nWordInLine);
var wordHeightPx = 60;
for (var i = 0; i < nLine; ++i) {
      var render_text = text.substr(i*nWordInLine, (i+1)*nWordInLine);
      context.fillText(render_text, 0, 200+(wordHeightPx*i));
}