openseadragon.js 是一款用來做圖像縮放的插件，它可以用來做圖片展示，做展示的插件很多，也很優秀，但大多數都解決不了圖片尺寸過大的問題。

藝術品圖像展示就是最簡單的例子，展示此類圖片一般要求比較精細，所以圖片尺寸很大，如果按照普通的方式直接將整個圖片加載，要耗費巨大的帶寬。

openseadragon.js 即為此而生，它展示的圖像，必須經過切割處理，當放大圖像時，才去加載更大的尺寸，真正做到了按需加載。

值得一提的是，openseadragon.js是微軟公司的一款開源產品，非常難得。

openseadragon.js用法很簡單。

定義html容器

1 <div id="container" style="width: 100%; height: 600px;"></div>

初始化openseadragon.js

 1 (function(win){ 2     var viewer = OpenSeadragon({ 3         // debugMode: true, 4         id: "container",  //容器id 5         xml",  //openseadragon 圖片資源xml 7         showNavigator:true  //是否顯示控制按鈕 8     }); 9     console.log(viewer);10 })(window);

效果圖

對，你沒有看錯，使用openseadragon.js，只需要copy一段初始化代碼，初始化代碼格式基本固定，只有tileSources是需要變化的，想顯示哪個圖，就寫哪個圖的xml鏈接。

那么這個xml是個什么東西呢？這是微軟定義的一套Deep Zoom技術，或者叫規范，通過圖像分割，然后配上一個xml文件，即可按照用戶縮放的尺寸，按需加載圖像，直到最清晰為止。這本來是微軟Silverlight里的技術，它的JavaScript實現就是openseadragon.js。

筆者從google code上找到了一份java程序，專門用來生成Deep Zoom。筆者在原作基礎上做了一些小小的改進，原作有些錯誤。。。

Deep Zoom For Java

  1 import java.awt.Graphics2D;  2 import java.awt.RenderingHints;  3 import java.awt.image.BufferedImage;  4 import java.io.File;  5 import java.io.FileOutputStream;  6 import java.io.IOException;  7 import java.nio.ByteBuffer;  8 import java.nio.channels.FileChannel;  9 import javax.imageio.ImageIO; 10  11 /** 12  * Deep Zoom Converter 13  *  14  * @author 楊元 15  * 16  */ 17 public class DeepZoomUtil { 18     static final String xmlHeader = "<?xml version=/"1.0/" encoding=/"utf-8/"?>"; 19     static final String schemaName = "http://schemas.microsoft.com/deepzoom/2009"; 20  21     static Boolean deleteExisting = true; 22     static String tileFormat = "jpg"; 23  24     // settings 25     static int tileSize = 256; 26     static int tileOverlap = 1; 27     static Boolean verboseMode = false; 28     static Boolean debugMode = false; 29  30     /** 31      * @param args the command line arguments 32      */ 33     public static void main(String[] args) { 34        35         try { 36             processImageFile(new File("d:/earth.jpg"), new File("d:/earth")); 37         } catch (Exception e) { 38             e.printStackTrace(); 39         } 40     } 41  42     /** 43      * Process the given image file, producing its Deep Zoom output files 44      * in a subdirectory of the given output directory. 45      * @param inFile the file containing the image 46      * @param outputDir the output directory 47      */ 48     private static void processImageFile(File inFile, File outputDir) throws IOException { 49         if (verboseMode) 50              System.out.printf("Processing image file: %s/n", inFile); 51  52         String fileName = inFile.getName(); 53         String nameWithoutExtension = fileName.substring(0, fileName.lastIndexOf('.')); 54         String pathWithoutExtension = outputDir + File.separator + nameWithoutExtension; 55  56         BufferedImage image = loadImage(inFile); 57  58         int originalWidth = image.getWidth(); 59         int originalHeight = image.getHeight(); 60  61         double maxDim = Math.max(originalWidth, originalHeight); 62  63         int nLevels = (int)Math.ceil(Math.log(maxDim) / Math.log(2)); 64  65         if (debugMode) 66             System.out.printf("nLevels=%d/n", nLevels); 67  68         // Delete any existing output files and folders for this image 69  70         File descriptor = new File(pathWithoutExtension + ".xml"); 71         if (descriptor.exists()) { 72             if (deleteExisting) 73                 deleteFile(descriptor); 74             else 75                 throw new IOException("File already exists in output dir: " + descriptor); 76         } 77  78         File imgDir = new File(pathWithoutExtension); 79         if (imgDir.exists()) { 80             if (deleteExisting) { 81                 if (debugMode) 82                     System.out.printf("Deleting directory: %s/n", imgDir); 83                 deleteDir(imgDir); 84             } else 85                 throw new IOException("Image directory already exists in output dir: " + imgDir); 86         } 87  88         imgDir = createDir(outputDir, nameWithoutExtension.concat("_files")); 89  90         double width = originalWidth; 91         double height = originalHeight; 92  93         for (int level = nLevels; level >= 0; level--) { 94             int nCols = (int)Math.ceil(width / tileSize); 95             int nRows = (int)Math.ceil(height / tileSize); 96             if (debugMode) 97                 System.out.printf("level=%d w/h=%f/%f cols/rows=%d/%d/n", 98                                    level, width, height, nCols, nRows); 99             100             File dir = createDir(imgDir, Integer.toString(level));101             for (int col = 0; col < nCols; col++) {102                 for (int row = 0; row < nRows; row++) {103                     BufferedImage tile = getTile(image, row, col);104                     saveImage(tile, dir + File.separator + col + '_' + row);105                 }106             }107 108             // Scale down image for next level109             width = Math.ceil(width / 2);110             height = Math.ceil(height / 2);111             if (width > 10 && height > 10) {112                 // resize in stages to improve quality113                 image = resizeImage(image, width * 1.66, height * 1.66);114                 image = resizeImage(image, width * 1.33, height * 1.33);115             }116             image = resizeImage(image, width, height);117         }118 119         saveImageDescriptor(originalWidth, originalHeight, descriptor);120     }121 122 123     /**124      * Delete a file125      * @param path the path of the directory to be deleted126      */127     private static void deleteFile(File file) throws IOException {128          if (!file.delete())129              throw new IOException("Failed to delete file: " + file);130     }131 132     /**133      * Recursively deletes a directory134      * @param path the path of the directory to be deleted135      */136     private static void deleteDir(File dir) throws IOException {137         if (!dir.isDirectory())138             deleteFile(dir);139         else {140             for (File file : dir.listFiles()) {141                if (file.isDirectory())142                    deleteDir(file);143                else144                    deleteFile(file);145             }146             if (!dir.delete())147                 throw new IOException("Failed to delete directory: " + dir);148         }149     }150 151     /**152      * Creates a directory153      * @param parent the parent directory for the new directory154      * @param name the new directory name155      */156     private static File createDir(File parent, String name) throws IOException {157         assert(parent.isDirectory());158         File result = new File(parent + File.separator + name);159         if (!result.mkdir())160            throw new IOException("Unable to create directory: " + result);161         return result;162     }163 164     /**165      * Loads image from file166      * @param file the file containing the image167      */168     private static BufferedImage loadImage(File file) throws IOException {169         BufferedImage result = null;170         try {171             result = ImageIO.read(file);172         } catch (Exception e) {173             throw new IOException("Cannot read image file: " + file);174         }175         return result;176     }177 178     /**179      * Gets an image containing the tile at the given row and column180      * for the given image.181      * @param img - the input image from whihc the tile is taken182      * @param row - the tile's row (i.e. y) index183      * @param col - the tile's column (i.e. x) index184      */185     private static BufferedImage getTile(BufferedImage img, int row, int col) {186         int x = col * tileSize - (col == 0 ? 0 : tileOverlap);187         int y = row * tileSize - (row == 0 ? 0 : tileOverlap);188         int w = tileSize + (col == 0 ? 1 : 2) * tileOverlap;189         int h = tileSize + (row == 0 ? 1 : 2) * tileOverlap;190 191         if (x + w > img.getWidth())192             w = img.getWidth() - x;193         if (y + h > img.getHeight())194             h = img.getHeight() - y;195 196         if (debugMode)197             System.out.printf("getTile: row=%d, col=%d, x=%d, y=%d, w=%d, h=%d/n",198                               row, col, x, y, w, h);199         200         assert(w > 0);201         assert(h > 0);202 203         BufferedImage result = new BufferedImage(w, h, img.getType());204         Graphics2D g = result.createGraphics();205         g.drawImage(img, 0, 0, w, h, x, y, x+w, y+h, null);206 207         return result;208     }209 210     /**211      * Returns resized image212      * NB - useful reference on high quality image resizing can be found here:213      *   http://today.java.net/pub/a/today/2007/04/03/perils-of-image-getscaledinstance.html214      * @param width the required width215      * @param height the frequired height216      * @param img the image to be resized217      */218     private static BufferedImage resizeImage(BufferedImage img, double width, double height) {219         int w = (int)width;220         int h = (int)height;221         BufferedImage result = new BufferedImage(w, h, img.getType());222         Graphics2D g = result.createGraphics();223         g.setRenderingHint(RenderingHints.KEY_INTERPOLATION,224                            RenderingHints.VALUE_INTERPOLATION_BICUBIC);225         g.drawImage(img, 0, 0, w, h, 0, 0, img.getWidth(), img.getHeight(), null);226         return result;227     }228 229     /**230      * Saves image to the given file231      * @param img the image to be saved232      * @param path the path of the file to which it is saved (less the extension)233      */234     private static void saveImage(BufferedImage img, String path) throws IOException {235         File outputFile = new File(path + "." + tileFormat);236         try {237             ImageIO.write(img, tileFormat, outputFile);238         } catch (IOException e) {239             throw new IOException("Unable to save image file: " + outputFile);240         }241     }242 243     /**244      * Write image descriptor XML file245      * @param width image width246      * @param height image height247      * @param file the file to which it is saved248      */249     private static void saveImageDescriptor(int width, int height, File file) throws IOException {250         StringBuilder sb = new StringBuilder(256);251         sb.append(xmlHeader);252         sb.append("<Image TileSize=/"");253         sb.append(tileSize);254         sb.append("/" Overlap=/"");255         sb.append(tileOverlap);256         sb.append("/" Format=/"");257         sb.append(tileFormat);258         sb.append("/" ServerFormat=/"Default/" xmlns=/"");259         sb.append(schemaName);260         sb.append("/">");261         sb.append("<Size Width=/"");262         sb.append(width);263         sb.append("/" Height=/"");264         sb.append(height);265         sb.append("/" />");266         sb.append("</Image>");267         saveText(sb.toString().getBytes("UTF-8"), file);268     }269 270     /**271      * Saves strings as text to the given file272      * @param bytes the image to be saved273      * @param file the file to which it is saved274      */275     private static void saveText(byte[] bytes, File file) throws IOException {276         try {277             //輸出流278             FileOutputStream fos = new FileOutputStream(file);279             //從輸出流中創建寫通道280             FileChannel writeChannel = fos.getChannel();281             //將既有數組作為buffer內存空間282             ByteBuffer byteBuffer = ByteBuffer.wrap(bytes);283             //將buffer寫到磁盤284             writeChannel.write(byteBuffer);285             286             writeChannel.close();287         } catch (IOException e) {288             throw new IOException("Unable to write to text file: " + file);289         }290     }291 }

調用非常簡單，只有一句話：processImageFile(new File("d:/earth.jpg"), new File("d:/earth"));，第一個參數是圖片路徑，第二個參數是生成的Deep Zoom保存路徑。本例將會在d:/earth目錄下生成一個earth.xml文件和一個earth_files文件夾，xml的文件名默認和圖片的文件名一致，然后直接把earth.xml的url返回給前端的openseadragon.js，就可以實現圖像縮放。

需要注意的是，*_files文件夾必須和xml文件在同一目錄，并且*要和xml文件名保持一致。

想要預覽openseadragon.js效果，必須在真實的http容器中，不可以直接在文件中打開。

打包的openseadragon.js筆者做了一些UI上的美化，個人覺得漂亮些，如果讀者不喜歡，可以用包里的原版。

openseadragon.js 世界地圖案例

openseadragon.js+java源碼打包下載