Delphi pdf reading components. Adding a PDF viewer to the program using ActiveX

Everyone has figured out the first part of the PDF.

What is the second part called ?

The answer is very simple: this is a sequence of objects, the description of which, as well as the header, are presented in text form.

Each object is a text fragment with a serial number in the name, for example "4 0 obj"

• 4 this is the object's serial number
• 0 this is the number of (re)generation of the file, that is, when the file is updated (edited), this number increases
• obj this is a code word meaning that we encountered an object in the body of the document

All objects are divided into indirect and direct. All are indirect, and most of them are after the word obj have a delimeter in their body"<<", означающее начало данных объекта. И в конце данных закрывающий делиметер ">>" and code word endobj

Direct objects should not have opening and closing delimiters in their body"<<", ">>>"All indirect objects are accessible through cross-reference table. It represents references in the form of an offset from the beginning of the file to the beginning of the object (Data (lines) in the object are separated #13#10 or #13 )

The type of the “most important” object in the body of a PDF file has a proud name "/Catalog"

4 0 obj<< /Type /Catalog /Pages 2 0 R /OpenAction [ 5 0 R /XYZ null 364 1 ] /PageMode /UseNone >>endobj

In fact, there should be 3 “main” objects in the body of a minimal “Hello world” PDF file. Let me list them by type:

• "/Catalog" contains a link: to the page tree ( /Pages)
• "/Pages" contains a link to a group of document pages (For example 2 0 obj > endobj)
• "/Page" contains a link to objects related to a specific page. (For example 3 0 obj > /Rotate 0 >>)

Let's analyze the page object:

• /Rotate a field indicating how many degrees the page image should be rotated when displayed in the program
• /MediaBox And /CropBox fields describing page size
• /Parent reference to parent object "/Pages"
• /Resources this field describes which font should be used when displaying the page (a font is a separate object) and the ProcSet setting this setting indicates what content is in the data stream of this page (can also be defined as an object, not as a field)
• /Contents The most interesting field in the “page” object gives a link to the content object of this page, and: if this field is absent in the “page” object, then the page is empty

The simplest option is an unencoded and uncompressed data stream in the object stream. It is limited to operators BT And ET

BT Begins a Text Object - characterizes the beginning of the text ET Ends a Text Object. - characterizes the end of the text /F12 9 Tf

• /F12 this is the code name of the object that characterizes the font used on this page
• 9 this is the font size
• Tf this is an operator that characterizes that this line in the steam object is the setting of the font and size

I don't explain the coded stream here. It is based on the RC4, RC5, MD5 algorithms.

What is an object Font 12 0 obj >

• /Type /Font Naturally the type name
• /Subtype /Type1 subtype name
• /Name /F7 F7 this is the code name

PDF supports several types of fonts. They are listed below

• Type 1, including subsets and Multiple Master "snapshots"
• Type 3
• TrueType, including subsets
• Type 0

20 0 obj > endobj This is an object with code names for fonts of the first type. Using this code name you can easily get the object itself font. 6 0 obj >

ALL: that is, the minimum Consists of the following objects: "catalog" , "pages", "page", "Resources"(can optionally be present as a field in the page object), untyped object "stream", group of objects "font"

What's happened ? In fact, this is an ordinary text table, it begins with the word xref and its body has links to all indirect objects in the document. Here is an example xref 0 27 0000000021 65535 f 0000000016 00000 n 0000000105 00000 n 0000000169 00000 n 0000000356 00000 n 0000000713 00000 n 00892 00000 n 0000001006 00000 n 0000001125 00000 n 0000001247 00000 n 0000001373 00000 n 0000001486 00000 n 0000001604 00000 n 0001725 00000 n 0000001850 00000 n 0000001967 00000 n 0000002084 00000 n 0000002203 00000 n 0000002326 00000 n 0000002439 00000 n 0000002558 00000 n 0000000024 000 01 f 0000002751 00000 n 0000002831 00000 n 0000000000 00001 f 0000002915 00000 n 0000002955 00000 n 0 27 These numbers mean the following:

• 0 - first object number in the table
• 27 - number of table elements

The first table element always has the form " XXXXXXXXXX 65535 f" where X is a digit and 65535 is the default value for the first element in the table. The symbol "f" stands for " free", that is, the object is not used

Let's analyze the element of this table.

• The first 10 digits are the offset from the beginning of the file to the beginning of the object.
• 0000000016 means that 16 bytes from the beginning of the file you will encounter the first mention of the object, that is, for example, 4 0 obj

The second five digits are the file generation number. If the file has just been created, then they are always zero. If the file is modified, then this number increases by one. That is, 0000000024 00001 f

The canonical PDF file we just created has only one table. But, if the file is edited, then there can be a lot of such tables.

The relationship of tables is carried out using the last element and code word startxref

The canonical, newly created PDF file has only one table, after the table there is an element trailer And after the trailer comes the code word startxref, indicating the offset from the start of the file to the start of the table, here's an example. trailer > startxref 173 %%EOF This means that after 173 bytes from the beginning of the document, the code word will be present xref. But, if the file has been edited, then the last trailer in the file will look like: xref 0 3 0000000000 65535 f 0000003609 00000 n 0000003832 00000 n trailer<7a15ab3ed3999575ff2f3034104a82c1>] >> startxref 173 %%EOF But, if we refer to the table where the link points startxref 173, then we will find the following table, and behind it a trailer that will have a field /Prev 3896 3 16 0000000016 00000 n 0000000664 00000 n 0000000936 00000 n 0000001106 00000 n 0000001133 00000 n 0000001250 00000 n 000000139 5 00000 n 0000001811 00000 n 0000001992 00000 n 0000002180 00000 n 0000002360 00000 n 0000002760 00000 n 0000003438 00000 n 516 00000 n 0000000776 00000 n 0000000916 00000 n trailer<7a15ab3ed3999575ff2f3034104a82c1>] >> startxref 567 %%EOF

This field /Prev 3896 points us to the previous table, and the link startxref 567 points to the next table and so on almost ad infinitum, until in the next field startxref we won't see 0 . This means we have read all the tables.

This essay, of course, lacks source code. Here it is: two main modules are presented" PDFDocument"and auxiliary" PDFBaseFonts"

The following files are attached to the material:

• Source code of modules PDFDocument.pas and PDFBaseFonts.pas (16 K) update from 9/23/2005 7:02:00 AM

Discussion of the material [ 07/31/2006 06:33 ] 7 messages

In this article, we'll look at how to create your own pdf-documents, and in the next article we’ll look at how you can view pdf-documents in your projects, as well as print content, navigate through the document, and so on.

For this we need the components from the tab Rave. Let's install the components we need to work, and these are:

• TRvNDRWriter
• TRvRenderPdf
• TButton

Component TRvNDRWriter intended for recording in pdf-file information (text, graphic) via stream.

Component TRvRenderPdf designed for creating and drawing information (text, graphic, etc.). Well, when you press a button, we will enter something into our pdf-file.

We won’t write much about theory, but let’s move straight to programming, but we must first create a regular empty pdf-file and put it in the root of the program. Next to the event OnClick For our button we will write the following code:

procedure TForm1. Button1Click(Sender: TObject); var Streams: TMemoryStream; begin Streams: = TMemoryStream. create ; RvNDrWriter1. Stream := Streams; RvNDRWriter1. Execute ; RvRenderPdf1. PrintRender(Streams, "test.pdf"); ShellExecute(Handle, nil, "test.pdf" , "" , "" , SW_SHOW) ; FreeAndNil(Streams); end ;

We create a stream in which we will draw all the information, then we start rendering, specify the file into which the data will be drawn, and at the end we destroy the stream.

That's it now, we need an event that occurs when drawing data, in which we will display all our information. Selecting the component TRvNDRWriter and go through the list of events of this component, after which we find the event OnPrint and in this event we write the following code:

procedure TForm1. Print(Sender: TObject); begin bmp: = TBitmap. Create ; bmp. LoadFromFile("test.bmp"); with RvNDRWriter1 do begin SetFont("Arial" , 16) ; FontColor: = clGreen; Print("Test Text" ) ; PrintHeader("Begin PDF File" , pjCenter) ; PrintFooter("End PDF File" , pjCenter) ; LineTo(10, 10) ; PrintBitmap(1, 1, 1, 1, bmp) ; end ; FreeAndNil(bmp); end ;

Well, first, we upload the image. *.bmp, naturally variable bmp, we have a class object TBitmap. We download it in order to then draw it in our pdf-document.

And then, I think everything is clear, the procedure PrintHeader- displays the inscription in the title of the document (page), procedure PrintFooter- displays the inscription at the end of the document (page). Procedure PrintBitmap- outputs an image to a document, procedure SetFont- sets the document font, procedure FontColor- sets the document font color.

There are two main ways to organize viewing of PDF documents in the program.

• Using ActiveX technology;
• Use of special components.

Components for working with PDF are not available in all Delphi releases and most often they need to be searched for and installed additionally. At the same time, to use ActiveX you only need to have the appropriate software on the user's computer. In this case, Adobe Acrobat Reader (free) or Adobe Acrobat.

Working with ActiveX can be divided into two stages.

• Importing a type library or components;
• Actually, the use of imported tools in the application.

Importing componentsActiveX

To import components, use the “Component” – “Import Component” command in the Delphi main menu. The import process itself is implemented as a wizard.

On the first page of the wizard, select “Import ActiveX Control”.

After this, you need to decide what to do with the imported components. Since we plan to use them as Delphi components, select “Install to New Package”.

Now all that remains is to specify the name of the newly created package.

After clicking on the "Finish" button, the PDF viewer ActiveX components will be imported into Delphi.

ViewPDF in attachment

To create a PDF viewer in an application using ActiveX, you need the TAcroPDF component. The process of importing it is described in detail above.

As an example, let's create the following application. Let's place the TAcroPDF, TOpenDialog and TButton components on the form as shown in the screenshot below.

When you click the button, we call up a file open dialog to select a PDF file to view.

For this example, we will need the following components, which are located in the Rave tab. And so, let's start installing the components we need, namely:

• TRvNDRWriter
• TRvRenderPdf
• TButton

I propose to dwell a little on these components and understand what they serve. By the way, I got information about them from a couple of books that I purchased progbook.ru. Therefore, if you want to buy decent books on Delphi, then you are welcome to this store.

So, first we have the TRvNDRWriter component. We need this component to write information to a pdf file, no matter what, text or graphic, through a stream.

Procedure TForm1.Button1Click(Sender: TObject); var Streams:TMemoryStream; begin Streams:=TMemoryStream.create; RvNDrWriter1.Stream:=Streams; RvNDRWriter1.Execute; RvRenderPdf1.PrintRender(Streams, "test.pdf"); ShellExecute(Handle, nil, "test.pdf", "", "", SW_SHOW); FreeAndNil(Streams); end;

The next component is TRvRenderPdf. We need it to create, or rather to draw, information, be it text or graphic. Accordingly, after clicking the button, we will write the information we need into our pdf file.

But let’s not rant too much, but let’s move straight to the topic that interests us, namely programming :)

First, we need to create a regular empty pdf file and place it in the root folder of our program.

Actually, with this code we create a stream where we will draw the information we need, after which we start rendering, indicate our final pdf file into which the data will be drawn, and at the end we close the stream.

After executing this when, we need an event that occurs when drawing data; in this event we will display the information we need.

Let's look at the code. To begin with, I load a *.bmp image, create a bmp variable, and an object of the TBitmap class. I download it so that I can then draw in our pdf file.

I think it’s not worth describing everything further clearly, and so, the PrintHeader procedure adds an inscription to the document header, the PrintFooter procedure adds an inscription to the end of the document. The PrintBitmap procedure adds an image to the document, the SetFont procedure sets the required document font, the FontColor procedure sets the desired document font color.

All subsequent graphic functions and procedures are exactly the same as when displaying graphic information on Canvas of other components.

I use the NewPage function to create a new sheet in a document. Everything that will be added after it to display information will be displayed on a new sheet of the document.

Important so that all modules: RpRender, RpRenderPDF, RpDefine, RpBase, RpFiler, RpRave, RpCon are connected to the project!