HTML5 Canvas Basics

<!DOCTYPE html>

<html>
<head>
  <title>MemeMaker-Simple</title>

  <meta name="viewport" content="width=device-width, initial-scale=1.0, maximum-scale=1.0">
  <meta name="mobile-web-app-capable" content="yes">
  <meta name="apple-mobile-web-app-capable" content="yes">
  <style>
    #image-container {
      display: flex;
    }
  </style>
</head>

<body>

  <div>
    <input type="file" id="file" />  
  </div>
  <div id="image-container">
    <canvas width="500" height="500"></canvas>
    <div>
      <span>Top Line:</span><br/>
      <input id="topLineText" type="text"><br/>
      <span>Bottom Line:</span><br/>
      <input id="bottomLineText" type="text"><br/>
      <button id="saveBtn">Save</button>
    </div>
  </div>
  <script>...</script>

</body>
</html>

function textChangeListener (evt) {
  var id = evt.target.id;
  var text = evt.target.value;

  if (id == "topLineText") {
    window.topLineText = text;
  } else {
    window.bottomLineText = text;
  }

  redrawMeme(window.imageSrc, window.topLineText, window.bottomLineText);
}

function redrawMeme(image, topLine, bottomLine) {
  // Get Canvas2DContext
  var canvas = document.querySelector('canvas');
  var ctx = canvas.getContext("2d");
  // Your code here

  ctx.font = "30pt Impact";
  ctx.textAlign = "center"; //기준좌표를 중심으로
  ctx.fillStyle = "white";
  ctx.lineWidth = "3";

  if (image) {
    ctx.drawImage(image, 0, 0);
    var imageData = ctx.getImageData(0,0,200, 200);
    var data = imageData.data;

    for(var i = 0; i < data.length; i += 4) {
      var brightness = 0.34 * data[i] + 0.5 * data[i + 1] + 0.16 * data[i + 2];
      // red
      data[i] = brightness;
      // green
      data[i + 1] = brightness;
      // blue
      data[i + 2] = brightness;
    }

    // overwrite original image
    ctx.putImageData(imageData, 0, 0);
  }

  if (topLine) {
    ctx.strokeText(topLine, 250, 100);
    ctx.fillText(topLine, 250, 100);
  }
  if (bottomLine) {
    ctx.strokeText(bottomLine, 250, 300);
    ctx.fillText(bottomLine, 250, 300);
  }
}

function saveFile() {
  window.open(document.querySelector('canvas').toDataURL());
}

function handleFileSelect(evt) {
  var canvasWidth = 500;
  var canvasHeight = 500;
  var file = evt.target.files[0];

  var reader = new FileReader();
  reader.onload = function(fileObject) {
    var data = fileObject.target.result;

    // Create an image object
    var image = new Image();
    image.onload = function() {

      window.imageSrc = this;
      redrawMeme(window.imageSrc, null, null);
    }

    // Set image data to background image.
    image.src = data;
    console.log(fileObject.target.result);
  };
  reader.readAsDataURL(file)
}

window.topLineText = "";
window.bottomLineText = "";
var input1 = document.getElementById('topLineText');
var input2 = document.getElementById('bottomLineText');
input1.oninput = textChangeListener;
input2.oninput = textChangeListener;
document.getElementById('file').addEventListener('change', handleFileSelect, false);
document.querySelector('button').addEventListener('click', saveFile, false);

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