Method and apparatus for downloading multi-page electronic documents with hint information

What is claimed is:

1. A method for downloading a multi-page electronic document which contains page offset information hints, hints being optional information added to the document to optimize operations, the method comprising:

reading the page offset information hints early during the downloading process;

receiving a request to download a specific page of the document, the document having elements defining the appearance of the specific page, the elements being stored in the document in a non-contiguous manner;

finding the non-contiguous elements of the specific page in the document using the page offset information hints which were downloaded early during the downloading process; and

downloading the elements defining the appearance of the specific page.

2. The method of claim 1 wherein the page offset information hints are located at a predetermined location in the document.

3. The method of claim 1 wherein the page offset information hints are read before the downloading of more than one page of the document has been completed.

4. The method of claim 1 wherein the beginning and ending offsets of each element needed to display a page of the document can be derived from the page offset information hints.

5. The method of claim 1 wherein, prior to reading the page offset information hints, an offset value is read from the document and used as an index into the document to locate the page offset information hints in the document.

6. The method of claim 5 wherein the offset value is read before or during the reading of the first page of the document.

7. The method of claim 1 wherein the page offset information hints are contained on or after the last page of the document.

8. The method of claim 1 wherein the page offset information hints are contained before the second page of the document.

9. The method of claim 1 further comprising a step of displaying the specific page requested by the user on an output display device.

10. The method of claim 9 wherein the specific page requested by the user is downloaded in one request-response transaction with a host computer which stores the multi-page document.

11. The method of claim 10 wherein the specific page includes page contents and shared objects, where the shared objects are downloaded interleaved between portions of the page contents.

12. The method of claim 9 wherein the specific page is requested by a user and is downloaded during one connection to a host computer which stores the multi-page document.

13. The method of claim 12 wherein said downloading is accomplished by a viewer program implemented on a client computer system operated by the user.

14. The method of claim 13 wherein a portion of the specific page is downloaded by the viewer while all remaining portions of the specific page are located by a finder process using the page offset information hints and downloaded during the one connection with the host computer.

15. The method of claim 14 wherein the remaining portions of the specific page include shared objects referenced by page contents of the specific page.

16. The method of claim 15 wherein the shared objects are downloaded interleaved between portions of the page contents that reference the shared objects.

17. The method of claim 1 wherein the specific page includes page contents and shared objects, where the shared objects are downloaded interleaved between portions of the page contents.

18. The method of claim 1 wherein the page offset information is stored in a page offset hint table in the document.

19. The method of claim 1 further comprising:

downloading shared object hints for the document, shared object hints providing information enabling a downloading process to locate shared objects in the document.

20. The method of claim 1 further comprising:

downloading bookmark hints for the document, bookmarks hints providing information enabling a downloading process to locate bookmarks in the document; and

downloading thumbnail hints for the document, thumbnail hints providing information enabling a downloading process to locate thumbnail in the document.

21. The method of claim 1 further comprising:

downloading article thread hints for the document, article thread hints providing information enabling a downloading process to locate article threads and beads in the document.

22. The method of claim 1 wherein:

the document includes at least one category of objects associated with particular pages and at least one category of objects associated with the document as a whole; and

each category of objects associated with the document as a whole has a corresponding hint table;

the method further comprising downloading the corresponding hint table.

23. A method for downloading a document including a plurality of pages from a remote host computer, comprising:

placing within the document page offset information hints specifying the exact location of the elements defining the appearance of each page of the document, hints being optional information not logically part of the structure or content of the document;

reading the page offset information hints early during the downloading process; and

using the page offset information hints to obtain and download a specific page requested by a user, the elements defining, the appearance of the specific page being stored in the document in a non-contiguous manner.

24. The method of claim 23 wherein the page offset information is read before the downloading of more than one page of the document has been completed.

25. The method of claim 23 further comprising displaying the specific page requested by the user on an output display device.

26. The method of claim 23 further comprising downloading page content information and shared objects for a first page of the document before said step of reading the page offset information hints.

27. The method of claim 26 further comprising initially downloading a range table to determine the location of the page content information and shared objects for the first page in the document.

28. The method of claim 26 further comprising a step of displaying a first page of the document as the page content information and shared objects for the first page are downloaded.

29. The method of claim 26 wherein the specific page requested by the user is downloaded in one request-response transaction with a host computer which stores the document.

30. The method of claim 26 wherein the specific page requested by the user is downloaded with one connection to a host computer which stores the document.

31. The method of claim 30 wherein a portion of the specific page is downloaded by a viewer process implemented by a client computer system operated by the user, while all remaining portions of the specific page are located in the document by a finder process using the page offset information hints, the remaining portions being downloaded during the one connection with the host computer.

32. The method of claim 31 wherein the remaining portions of the specific page include shared objects referenced by page contents of the specific page, wherein the shared objects are downloaded interleaved between portions of the page contents that reference the shared objects.

33. A computer readable storage medium including program instructions for performing steps during a downloading process for interleaving page contents of a page of a document with a shared object referenced by the page, the steps comprising:

downloading a first portion of page content of a page-based document stored on a host computer, the portion of page content including a reference to a shared object;

downloading the shared object referenced by the first portion of the page; and

downloading a second portion of page content of the page of the page-based document;

wherein the second portion of page content is stored contiguously with the first portion of page content on the host computer and the shared object is not stored contiguously with either the first portion of page content or the second portion of page content on the host computer.

34. A computer readable storage medium as recited in claim 33 wherein the shared object is stored on the host computer in the page-based document.

35. A computer readable storage medium as recited in claim 33 wherein the shared object is referenced by a plurality of pages of the document.

36. A computer readable storage medium as recited in claim 33 wherein the shared object is force to be a shared object regardless of whether the object is referenced by a plurality of pages, and wherein only predetermined types of object are forced to be shared objects.

37. A computer readable storage medium as recited in claim 33 wherein the program instructions further perform a step of deriving the locations of the first portion of page content, the second portion of page content, and the shared object in the page-based document utilizing a page offset table downloaded from the page-based document.

38. A computer readable storage medium as recited in claim 33 wherein the program instructions further perform a step of displaying the first portion and the second portion of page content on an output display device, and wherein the downloading of the shared object is necessary to display the first portion of page content.

39. A computer readable storage medium as recited in claim 38 wherein the page content includes text to be displayed, and wherein the shared object is a font object needed to display the text.

40. A computer readable storage medium as recited in claim 33 wherein the first portion and the second portion of page contents are predetermined fractions of the entire page contents for the page in the page-based document.

41. A computer readable storage medium as recited in claim 40 wherein a plurality of the fractions of page content are downloaded up to the fraction that includes the reference to the shared object.

42. A computer readable storage medium as recited in claim 41 wherein the shared object is stored in a shared object cache, wherein the shared object cache is checked to determine if a shared object has been previously downloaded before downloading the shared object.

43. An apparatus for downloading a page-based document stored on a host, the document containing page offset information hints located at a predetermined location, the apparatus comprising:

a digital processor;

a memory device coupled to the digital processor;

a display screen coupled to the digital processor;

means for displaying the page-based document on the display screen, the means for displaying connecting with the host to download the page offset information hints, to download a specific page of the page-based document requested by the user without the necessity of downloading other pages in the document, and to display the downloaded page on the display screen; and

a finder for utilizing the page offset information hints to provide a location of the specific page in the document to the means for displaying so that the means for displaying can download the specific page; wherein

when the means for displaying is downloading a portion of a specific page during a connection with the host, the finder additionally requests additional portions of the specific page and the additional portions of the page are downloaded to the means for displaying to be displayed, the additional portions including page contents and shared objects, the page contents including text and the shared objects including font objects, the finder requesting a portion of the page contents to be downloaded that includes a reference to a particular shared object and requesting the particular shared object to be downloaded after the portion of the page contents.

44. The apparatus of claim 43 wherein the page offset information hints are read before the downloading of more than one page of the document has been completed.

45. The apparatus of claim 43 wherein the finder can derive the beginning offsets of each page of the document from the page offset information hints.

46. The apparatus of claim 43 wherein the means for displaying includes a viewer process for selecting and displaying pages of the page-based document on the display screen.

47. Apparatus comprising a computer-readable storage medium tangibly embodying computer program instructions comprising instructions to:

connect with a host computer to download page offset information hints located at a predetermined location in a document;

download shared object hints from the host computer;

using the page offset information hints and the shared object hints, locate a first portion of page content of a page of the document, a second portion of page content of the page of the document, and a shared object in the document, the first portion of page content including a reference to the shared object;

download the located first portion of page content;

download the located shared object; and

download the located second, portion of content.

48. The apparatus of claim 47 wherein when a display process is downloading a portion of a specific page during a connection with the host computer, a finder process additionally requests additional portions of the specific page, and the additional portions of the page are downloaded to the display process to be displayed.

Description Submit all comments and votes

BACKGROUND OF THE INVENTION

The present invention relates generally to the storage and retrieval of data for a computer system, and more particularly to a method and apparatus for optimizing page-based data documents for fast retrieval over networks, and to a method and apparatus for accessing such optimized documents. The present invention also relates to methods and apparatus for the processing and display of electronic documents, and more particularly to the processing and display of such documents when retrieved over networks.

It has become increasingly common to create, transmit, and display documents in electronic form. Electronic documents have a number of advantages over paper documents including their ease of transmission, their compact storage, and their ability to be edited and/or electronically manipulated. An electronic document typically has information content (such as text, graphics, and pictures) and formatting information that directs how the content is to be displayed. With recent advances in multimedia technology, documents can now also include sound, full motion video, and other multimedia content.

An electronic document is provided by an author, distributor or publisher (referred to as "publisher" herein) who often desires that the document be viewed with the appearance with which it was created. This, however, creates a problem in that electronic documents are typically widely distributed and, therefore, can be viewed on a great variety of hardware and software platforms. For example, the video monitors being used to view the document can vary in size, resolution, etc. Furthermore, the various software platforms such as DOS, Microsoft Windows.TM., and Macintosh.TM. all have their own display idiosyncrasies. Also, each user or "reader" of the electronic document will have his or her own personal viewing preferences, which should be accommodated, if possible.

A solution to this problem is to provide a "portable electronic document" that can be viewed and manipulated on a variety of different platforms and can be presented in a predetermined format where the appearance of the document as viewed by a reader is as it was intended by the publisher. One such predetermined format is the Portable Document Format.TM. (PDF.TM.) developed by Adobe Systems, Inc. of Mountain View, Calif. An example of page-based software for creating, reading, and displaying PDF documents is the Acrobat.TM. software, also of Adobe Systems, Inc. The Adobe Acrobat software is based on Adobe's PostScript.RTM. technology, which describes formatted pages of a document in a device-independent fashion. An Acrobat program on one platform can create, display, edit, print, annotate, etc. a PDF document produced by another Acrobat program running on a different platform, regardless of the type of computer platform used. A document in a certain format or language can be translated into a PDF document using Acrobat. A PDF document can be quickly displayed on any computer platform having the appearance intended by the publisher, allowing the publisher to control the final appearance of the document.

One relatively new application for portable electronic documents is the retrieval of such documents from the "Internet", the globally-accessible network of computers that collectively provides a large amount and variety of information for users. From services of the Internet such as the World Wide Web, users may retrieve or "download" data from Internet network sites and display the data that includes information presented as text in various fonts, graphics, images, and the like having an appearance intended by the publisher. A file format such as PDF that allows any platform to view a document having an appearance as intended by a publisher is thus of great value when downloading files from such widely-accessible and platform-independent network sources such as the Internet.

One problem with previous page-based data downloading processes is that all of the data of a document is typically downloaded before any portion of the document is displayed to the user. Thus, the user must wait for an entire document to download before seeing a page or other portion of the document on the display screen. This can be inconvenient when the user wishes to use only a portion of the document, i.e., view only specific pages or a specific number of contiguous pages of a document. Some searching processes allow a word to be searched in a document and will download only the portion of the document that includes the searched word. However, this portion of the document is an isolated, separate portion that has no connection with the rest of the document. If the user wishes to view the next page after the downloaded portion, he or she must inconveniently either download the entire document or specify a search term on the next page of the document.

Acrobat and similar programs for displaying portable electronic documents such as PDF documents are often page-based, which means that the program typically organizes and displays a desired page of the document at a time. Typically, the entire document was downloaded at once, then desired pages displayed. However, Acrobat is conducive to downloading a page of a document at a time from a document file, while still allowing a user to select other pages of the document conveniently. However, for such page-based formats, the document data usually is not stored contiguously in a page order within a file, data structure, or other collection of document data ("document file" as referred to herein). For example, a document file in the PDF format may store a page having objects such as a page contents object (including text, graphics shapes, display instructions, etc.) and image objects. However, the objects may be stored in the document in a scattered or disjointed manner. For example, portions of the page contents object can be scattered in different places in a document file, and shared objects such as fonts can be stored anywhere in the file. Shared objects such as fonts can also be stored in files distinct from the document file, and even on a separate computer, or be made available through a resource service such as a font server. Since the output display device displays the page contents and shared objects based upon pointers to related objects, objects do not have to be stored sequentially or contiguously in the document file, and are typically stored in a disjointed manner.

This disjointed data storage for pages can lead to problems when attempting to download a specific page of a document desired by the user. One major problem is time delays caused by making multiple connections (or multiple request-response transactions) when downloading data. For example, a viewing program for displaying page-based data at a client computer begins downloading a PDF (or similar format) file from a remote host computer. The viewing program makes one connection to (or initiates one transaction with) the host and downloads data from the first portion of the page, then must make another connection to (or transactions with) the host to retrieve the next, disjointed portion of the page. This has the effect of slowing down the downloading of the page, since each connection (and each transaction) has a time delay and overhead associated with it. The user requesting the page thus may have to wait several seconds before the viewer receives all of the data for the page and displays the page. This problem is compounded when fonts or other such referenced objects are included on the page, since yet another connection must be made to (or transaction made with) the host to retrieve these objects before the page can be displayed.

The time delays for downloading a page can become even lengthier when a randomly-accessed page is desired to be viewed by the user. In PDF files, objects are provided in a "page tree" which the viewer consults to determine where in the document file the root of a randomly-accessed page is positioned. The page tree is a data structure in which every node must be visited in order to determine all the children objects in the tree. Thus, many page nodes may need to be visited to determine where a page root object is located in the document file. The page tree can thus be quite large, and downloading it from the document slows the downloading process. In addition, the page tree is often so large or disjointed that multiple connections to (or transactions with) the host are required to download it.

Therefore, there is a need for a method and apparatus for providing optimized page-based documents and downloading desired pages from such documents without causing an excessive delay before displaying a page, or portions of a page, to the user.

SUMMARY OF THE INVENTION

The present invention provides a method and apparatus for optimizing a page-based electronic document and downloading and displaying desired pages, or portions of a page, from the optimized document without excessive time delays.

A method of the present invention provides an optimized document file from a non-optimized electronic document having one or more pages. Page content information that describes individual pages of the document is written in the optimized document file. The page content information may be written contiguously. Page offset information used to locate individual pages of the document may also be provided in the optimized document file. Objects shared by multiple pages are also provided for in the optimized document file, contiguously located after all of the page content information, and the page offset information includes offsets (locations) to these shared objects. The page content information includes text and graphics, and the shared objects can include font objects and image objects. To provide the page contents and shared objects contiguously in the file, an internal list of non-shared objects and shared objects in the document file is created. A list of pages that share objects is also created that includes the shared objects used by each sharing page and, for each such shared object, a portion of the page contents in which the shared object is referenced. In addition, in one aspect, first page offset information may be provided in a range table for a first page of the optimized document file. Such first page offset information describes the locations of all portions of the first page in the document file. The offsets to page content for this page may be interleaved in the range table with offsets to shared objects referenced by the page content for the first page.

Another method of the present invention efficiently downloads a page-based optimized document created as described above. The page offset information is read early during the downloading process. Beginning and ending offsets of each page of the document can be derived from the page offset information. Using the page offset information, a specific page requested by the user is downloaded, and any page desired by the user can readily be downloaded without the necessity of downloading other pages in the document. In one aspect of the method, the page offset information may be read before the downloading of more than one page of the document has been completed. In one aspect, the document file has a pointer that points to the location of the page offset information, which pointer is read ahead of, or during, the reading of the first page of the document.

In another aspect, when a user requests a specific page of an optimized document, the specific page is downloaded to a client computer system in only one connection with a host that stores the optimized document file. In another aspect, the specific page is downloaded in only one transaction with the host. The requested page, while being downloaded, may be displayed to the user on an output display device, such as a display screen, monitor, or printer. The downloading can be accomplished by a viewer program on the client computer system. When connecting and downloading, the viewer may download a first portion of the requested page, while all remaining portions of the requested page are located and requested by a finder process on the client computer using the page offset table. These additional portions are downloaded during the client computer's one connection with the host, thus saving time and overhead by avoiding multiple transactions or connections. The additional portions of the specific page may include shared objects referenced by page contents of the specific page. Shared objects are downloaded in an interleaved order between portions of the page contents that reference the shared objects. In another aspect, the requested page is downloaded to a client computer system in only one transaction with a host that stores the optimized document file, the transaction being constructed by a process using a page offset hint table and any other hint tables available in the document.

If shared objects are downloaded in an interleaved order, the interleaving process includes downloading a first portion of page content from the requested page, where the first portion of page content includes a reference to a shared object. The first portion may include all contiguous page content of the document until the (approximate) point of reference to the shared object. Then, the shared object referenced by the first portion of the page is downloaded. The shared object is, for example, a font or similar referenced object that is needed to display the first portion of page content. A second portion of page content from the requested page is then downloaded, where the second portion is contiguous with the first portion of page content. The locations of the first and second portions of page content and the shared objects in the page-based document are derived using the page offset table. Alternatively, a surrogate, such as a substitute font, is used to display the first portion of page content, thereby allowing the process to defer the downloading of the referenced object and thereby to download and to display more quickly the second portion of page content.

Another method of the present invention provides for the displaying on a display device of a computer an electronic document, such as a portable electronic document, having text to be displayed on top of a large object, such as a bitmap image. In general, in one aspect, the method includes displaying the display of the large object in favor of displaying the overlying text, displaying the overlying text on the display device, and at least as to that portion of the large object that appears underneath the overlying text, drawing the underneath portion into an off-screen buffer, drawing the overlying text over the object in the off-screen buffer and copying the off-screen buffer to be displayed on the display device. In another aspect, the acts of displaying an object and of displaying text include rendering a bitmap of at least one bit per pixel into a display buffer of random access memory. In another aspect, the display buffer and the off-screen buffer have the same pixel depths and color definitions. In another aspect, the invention provides for creating a blocking mask corresponding to the displayed appearance of the text and then displaying the portion of the object that is specified to appear as if drawn underneath the text under control of the blocking mask so that displaying the object does not overwrite the displayed text.

Another method of the present invention is implemented in a viewing program to display to a user an electronic document, such as a portable electronic document, that contains an interactive element responsive to user input. In one aspect, the method includes changing the appearance of the cursor of the viewing program's graphical user interface to indicate when it is located in a position where the interactive element will be displayed, and making the interactive element responsive to input from the user without waiting for the interactive element to be displayed. In another aspect, the interactive element is a hypertext link. In another aspect, the interactive element is an annotation in a PDF format electronic document.

Another method of the present invention provides for displaying on a computer display device an electronic document, such as a portable electronic document, that has text in a desired font, without waiting for the desired font to be available. In one aspect, the method includes initially drawing on the display device at least a part of the text in a substitute font different from the desired font, obtaining the desired font for use on the computer with the display device, and redrawing with the desired font the area of display in which the substitute font had been used initially. In another aspect, the method includes reading font description metrics for the desired font and using them to create a substitute font. In another aspect, the method also includes adopting a font from available font resources as the substitute font. In another aspect, the desired font is a font included as an embedded font in the document. In another aspect, the desired font is obtained from a font server.

An apparatus of the present invention provides for efficiently downloading a page-based document stored on a host, as described above. The apparatus includes a digital processor, a memory device, and a display screen. Furthermore, a mechanism for displaying the page-based document on the display screen is included which connects with the host to download the page offset information and/or to download a specific page of the document requested by the user without downloading other pages in the document. A downloaded page can be displayed on the display screen. A finder uses the page offset information to provide a location of the specific page in the document to the displaying mechanism so that the specific page can be downloade