extensions/renderer/resources/image_util.js

   1 // Copyright 2014 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 // This function takes an object |imageSpec| with the key |path| -
   6 // corresponding to the internet URL to be translated - and optionally
   7 // |width| and |height| which are the maximum dimensions to be used when
   8 // converting the image.
   9 function loadImageData(imageSpec, callbacks) {
  10   var path = imageSpec.path;
  11   var img = new Image();
  12   if (typeof callbacks.onerror === 'function') {
  13     img.onerror = function() {
  14       callbacks.onerror({ problem: 'could_not_load', path: path });
  15     };
  16   }
  17   img.onload = function() {
  18     var canvas = document.createElement('canvas');
  19
  20     if (img.width <= 0 || img.height <= 0) {
  21       callbacks.onerror({ problem: 'image_size_invalid', path: path});
  22       return;
  23     }
  24
  25     var scaleFactor = 1;
  26     if (imageSpec.width && imageSpec.width < img.width)
  27       scaleFactor = imageSpec.width / img.width;
  28
  29     if (imageSpec.height && imageSpec.height < img.height) {
  30       var heightScale = imageSpec.height / img.height;
  31       if (heightScale < scaleFactor)
  32         scaleFactor = heightScale;
  33     }
  34
  35     canvas.width = img.width * scaleFactor;
  36     canvas.height = img.height * scaleFactor;
  37
  38     var canvas_context = canvas.getContext('2d');
  39     canvas_context.clearRect(0, 0, canvas.width, canvas.height);
  40     canvas_context.drawImage(img, 0, 0, canvas.width, canvas.height);
  41     try {
  42       var imageData = canvas_context.getImageData(
  43           0, 0, canvas.width, canvas.height);
  44       if (typeof callbacks.oncomplete === 'function') {
  45         callbacks.oncomplete(
  46             imageData.width, imageData.height, imageData.data.buffer);
  47       }
  48     } catch (e) {
  49       if (typeof callbacks.onerror === 'function') {
  50         callbacks.onerror({ problem: 'data_url_unavailable', path: path });
  51       }
  52     }
  53   }
  54   img.src = path;
  55 }
  56
  57 function on_complete_index(index, err, loading, finished, callbacks) {
  58   return function(width, height, imageData) {
  59     delete loading[index];
  60     finished[index] = { width: width, height: height, data: imageData };
  61     if (err)
  62       callbacks.onerror(index);
  63     if ($Object.keys(loading).length == 0)
  64       callbacks.oncomplete(finished);
  65   }
  66 }
  67
  68 function loadAllImages(imageSpecs, callbacks) {
  69   var loading = {}, finished = [],
  70       index, pathname;
  71
  72   for (var index = 0; index < imageSpecs.length; index++) {
  73     loading[index] = imageSpecs[index];
  74     loadImageData(imageSpecs[index], {
  75       oncomplete: on_complete_index(index, false, loading, finished, callbacks),
  76       onerror: on_complete_index(index, true, loading, finished, callbacks)
  77     });
  78   }
  79 }
  80
  81 exports.loadImageData = loadImageData;
  82 exports.loadAllImages = loadAllImages;