| // Copyright (c) 2012 The Chromium Authors. All rights reserved. |
| // Use of this source code is governed by a BSD-style license that can be |
| // found in the LICENSE file. |
| |
| 'use strict'; |
| |
| /** |
| * A namespace class for image encoding functions. All methods are static. |
| */ |
| function ImageEncoder() {} |
| |
| /** |
| * @type {Array.<Object>} |
| */ |
| ImageEncoder.metadataEncoders = {}; |
| |
| /** |
| * @param {function(new:ImageEncoder.MetadataEncoder)} constructor |
| * // TODO(JSDOC). |
| * @param {string} mimeType // TODO(JSDOC). |
| */ |
| ImageEncoder.registerMetadataEncoder = function(constructor, mimeType) { |
| ImageEncoder.metadataEncoders[mimeType] = constructor; |
| }; |
| |
| /** |
| * Create a metadata encoder. |
| * |
| * The encoder will own and modify a copy of the original metadata. |
| * |
| * @param {Object} metadata Original metadata. |
| * @return {ImageEncoder.MetadataEncoder} Created metadata encoder. |
| */ |
| ImageEncoder.createMetadataEncoder = function(metadata) { |
| var constructor = ImageEncoder.metadataEncoders[metadata.mimeType] || |
| ImageEncoder.MetadataEncoder; |
| return new constructor(metadata); |
| }; |
| |
| |
| /** |
| * Create a metadata encoder object holding a copy of metadata |
| * modified according to the properties of the supplied image. |
| * |
| * @param {Object} metadata Original metadata. |
| * @param {HTMLCanvasElement} canvas Canvas to use for metadata. |
| * @param {number} quality Encoding quality (defaults to 1). |
| * @return {ImageEncoder.MetadataEncoder} Encoder with encoded metadata. |
| */ |
| ImageEncoder.encodeMetadata = function(metadata, canvas, quality) { |
| var encoder = ImageEncoder.createMetadataEncoder(metadata); |
| encoder.setImageData(canvas); |
| encoder.setThumbnailData(ImageEncoder.createThumbnail(canvas), quality || 1); |
| return encoder; |
| }; |
| |
| |
| /** |
| * Return a blob with the encoded image with metadata inserted. |
| * @param {HTMLCanvasElement} canvas The canvas with the image to be encoded. |
| * @param {ImageEncoder.MetadataEncoder} metadataEncoder Encoder to use. |
| * @param {number} quality (0..1], Encoding quality, defaults to 0.9. |
| * @return {Blob} encoded data. |
| */ |
| ImageEncoder.getBlob = function(canvas, metadataEncoder, quality) { |
| // Contrary to what one might think 1.0 is not a good default. Opening and |
| // saving an typical photo taken with consumer camera increases its file size |
| // by 50-100%. |
| // Experiments show that 0.9 is much better. It shrinks some photos a bit, |
| // keeps others about the same size, but does not visibly lower the quality. |
| quality = quality || 0.9; |
| |
| ImageUtil.trace.resetTimer('dataurl'); |
| // WebKit does not support canvas.toBlob yet so canvas.toDataURL is |
| // the only way to use the Chrome built-in image encoder. |
| var dataURL = |
| canvas.toDataURL(metadataEncoder.getMetadata().mimeType, quality); |
| ImageUtil.trace.reportTimer('dataurl'); |
| |
| var encodedImage = ImageEncoder.decodeDataURL(dataURL); |
| |
| var encodedMetadata = metadataEncoder.encode(); |
| |
| var slices = []; |
| |
| // TODO(kaznacheev): refactor |stringToArrayBuffer| and |encode| to return |
| // arrays instead of array buffers. |
| function appendSlice(arrayBuffer) { |
| slices.push(new DataView(arrayBuffer)); |
| } |
| |
| ImageUtil.trace.resetTimer('blob'); |
| if (encodedMetadata.byteLength != 0) { |
| var metadataRange = metadataEncoder.findInsertionRange(encodedImage); |
| appendSlice(ImageEncoder.stringToArrayBuffer( |
| encodedImage, 0, metadataRange.from)); |
| |
| appendSlice(metadataEncoder.encode()); |
| |
| appendSlice(ImageEncoder.stringToArrayBuffer( |
| encodedImage, metadataRange.to, encodedImage.length)); |
| } else { |
| appendSlice(ImageEncoder.stringToArrayBuffer( |
| encodedImage, 0, encodedImage.length)); |
| } |
| var blob = new Blob(slices, {type: metadataEncoder.getMetadata().mimeType}); |
| ImageUtil.trace.reportTimer('blob'); |
| return blob; |
| }; |
| |
| /** |
| * Decode a dataURL into a binary string containing the encoded image. |
| * |
| * Why return a string? Calling atob and having the rest of the code deal |
| * with a string is several times faster than decoding base64 in Javascript. |
| * |
| * @param {string} dataURL Data URL to decode. |
| * @return {string} A binary string (char codes are the actual byte values). |
| */ |
| ImageEncoder.decodeDataURL = function(dataURL) { |
| // Skip the prefix ('data:image/<type>;base64,') |
| var base64string = dataURL.substring(dataURL.indexOf(',') + 1); |
| return atob(base64string); |
| }; |
| |
| /** |
| * Return a thumbnail for an image. |
| * @param {HTMLCanvasElement} canvas Original image. |
| * @param {number=} opt_shrinkage Thumbnail should be at least this much smaller |
| * than the original image (in each dimension). |
| * @return {HTMLCanvasElement} Thumbnail canvas. |
| */ |
| ImageEncoder.createThumbnail = function(canvas, opt_shrinkage) { |
| var MAX_THUMBNAIL_DIMENSION = 320; |
| |
| opt_shrinkage = Math.max(opt_shrinkage || 4, |
| canvas.width / MAX_THUMBNAIL_DIMENSION, |
| canvas.height / MAX_THUMBNAIL_DIMENSION); |
| |
| var thumbnailCanvas = canvas.ownerDocument.createElement('canvas'); |
| thumbnailCanvas.width = Math.round(canvas.width / opt_shrinkage); |
| thumbnailCanvas.height = Math.round(canvas.height / opt_shrinkage); |
| |
| var context = thumbnailCanvas.getContext('2d'); |
| context.drawImage(canvas, |
| 0, 0, canvas.width, canvas.height, |
| 0, 0, thumbnailCanvas.width, thumbnailCanvas.height); |
| |
| return thumbnailCanvas; |
| }; |
| |
| /** |
| * TODO(JSDOC) |
| * @param {string} string // TODO(JSDOC). |
| * @param {number} from // TODO(JSDOC). |
| * @param {number} to // TODO(JSDOC). |
| * @return {ArrayBuffer} // TODO(JSDOC). |
| */ |
| ImageEncoder.stringToArrayBuffer = function(string, from, to) { |
| var size = to - from; |
| var array = new Uint8Array(size); |
| for (var i = 0; i != size; i++) { |
| array[i] = string.charCodeAt(from + i); |
| } |
| return array.buffer; |
| }; |
| |
| /** |
| * A base class for a metadata encoder. |
| * |
| * Serves as a default metadata encoder for images that none of the metadata |
| * parsers recognized. |
| * |
| * @param {Object} original_metadata Starting metadata. |
| * @constructor |
| */ |
| ImageEncoder.MetadataEncoder = function(original_metadata) { |
| this.metadata_ = MetadataCache.cloneMetadata(original_metadata) || {}; |
| if (this.metadata_.mimeType != 'image/jpeg') { |
| // Chrome can only encode JPEG and PNG. Force PNG mime type so that we |
| // can save to file and generate a thumbnail. |
| this.metadata_.mimeType = 'image/png'; |
| } |
| }; |
| |
| /** |
| * TODO(JSDOC) |
| * @return {Object} // TODO(JSDOC). |
| */ |
| ImageEncoder.MetadataEncoder.prototype.getMetadata = function() { |
| return this.metadata_; |
| }; |
| |
| /** |
| * @param {HTMLCanvasElement|Object} canvas Canvas or or anything with |
| * width and height properties. |
| */ |
| ImageEncoder.MetadataEncoder.prototype.setImageData = function(canvas) { |
| this.metadata_.width = canvas.width; |
| this.metadata_.height = canvas.height; |
| }; |
| |
| /** |
| * @param {HTMLCanvasElement} canvas Canvas to use as thumbnail. |
| * @param {number} quality Thumbnail quality. |
| */ |
| ImageEncoder.MetadataEncoder.prototype.setThumbnailData = |
| function(canvas, quality) { |
| this.metadata_.thumbnailURL = |
| canvas.toDataURL(this.metadata_.mimeType, quality); |
| }; |
| |
| /** |
| * Return a range where the metadata is (or should be) located. |
| * @param {string} encodedImage // TODO(JSDOC). |
| * @return {Object} An object with from and to properties. |
| */ |
| ImageEncoder.MetadataEncoder.prototype. |
| findInsertionRange = function(encodedImage) { return {from: 0, to: 0} }; |
| |
| /** |
| * Return serialized metadata ready to write to an image file. |
| * The return type is optimized for passing to Blob.append. |
| * @return {ArrayBuffer} // TODO(JSDOC). |
| */ |
| ImageEncoder.MetadataEncoder.prototype.encode = function() { |
| return new Uint8Array(0).buffer; |
| }; |