Fixed version of CoursesWeb's Tutorial: Add Canvas from Input Field Typed

add-text-canvas-from-input-field-typed_cs_fixed.html

<!-- fixed version of http://coursesweb.net/javascript/add-text-canvas-from-input-field-typed_cs -->

<h4>Canvas</h4><canvas width="350" height="180" id="cnv1"></canvas><br/>
Text: <input type="text" id="text_cnv" size="40" maxlength="250" />
<script type="text/javascript">

// function to clear the canvas
// cnv = the object with the canvas element
function clearCanvas(cnv) {
  var ctx = cnv.getContext('2d');     // gets reference to canvas context
  ctx.beginPath();    // clear existing drawing paths
  ctx.save();         // store the current transformation matrix

  // Use the identity matrix while clearing the canvas
  ctx.setTransform(1, 0, 0, 1, 0, 0);
  ctx.clearRect(0, 0, cnv.width, cnv.height);

  ctx.restore();        // restore the transform
}

// adds the text in canvas, oon multiple lines
// ctx = reference to canvas context
// text = the text to add
// x = horizontal position where to start adding the text
// y = vertical position where to start adding the text
// maxWidth = the maximum width of the text line
//  lineHeight = the height of the line
function  addTextCnv(ctx, text, x, y, maxWidth, lineHeight) {
  // splits the text in words to can wrap it on new lie if exceds maxWidth
  var words = text.split(' ');
  var nr_w = words.length
  var addtxt = '';

  // sets to add the text and rows
  for(var n = 0; n < nr_w; n++) {
    var txtLine = addtxt + words[n] + ' ';
    var metrics = ctx.measureText(txtLine);
    var txtWidth = metrics.width;
    if (txtWidth > maxWidth && n > 0) {
      ctx.fillText(addtxt, x, y);
      addtxt = words[n] + ' ';
      y  = lineHeight;
    }
    else addtxt = txtLine;
  }

  // adds the text in canvas (sets text color, font type and size)
  ctx.fillStyle = '#0001be';
  ctx.font = 'bold 17px sans-serif';
  ctx.fillText(addtxt, x, y);
}

// get a reference to the canvas element, and its context
var cnv1 = document.getElementById('cnv1');
var ctx1 = cnv1.getContext('2d');

// sets maximum line width, line height, and x /y coords for text
var maxWidth = cnv1.width - 10;
var lineHeight = 23;
var x_pos = (cnv1.width - maxWidth) / 2;
var y_pos = 15;

// register onkeyup event for #text_cnv text field to add the text in canvas as it is typed
document.getElementById('text_cnv').onkeyup = function() {
  clearCanvas(cnv1);      // clears the canvas
  addTextCnv(ctx1, this.value, x_pos, y_pos, maxWidth, lineHeight);
}

</script>