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Home » Newsletter » February 2010

By L. Santhanam

If your application generates PDF documents in real time, then why not show snapshots of the document dynamically? In the ProPlus edition of PDFOne .NET, the PDFDocument component has certain methods that allow you to export images of PDF pages. They are RenderOnGraphics() and GetPageMetafile(). In the following code example, you will see how to use the RenderOnGraphics() method. This code snippet uses a bitmap, which will then be used to render the Graphics item. The bitmap is saved to a file only to demonstrate the results.

using System;
using System.Collections.Generic;
using System.Text;
using System.Drawing;
using System.Drawing.Imaging;
using System.Drawing.Drawing2D;
using Gnostice.PDFOne;

class RenderOnGraphicsDemo
{

    static void Main(string[] args)
    {
        // Determine current DPI
        Graphics Graphics1 = Graphics.FromHwndInternal(IntPtr.Zero);
        int DPI = (int) Graphics1.DpiX;
        Graphics1.Dispose();

        // Load a PDF document
        PDFDocument PDFDocument1 = new PDFDocument("your-license-key");
        PDFDocument1.Load("sample_doc.pdf");

        // Get page 3 from the document
        PDFPage PDFPage1 = PDFDocument1.GetPage(3);

        // Get dimensions of page 3 in pixels
        int PageWidth = DPI * ((int)PDFPage1.GetWidth(PDFMeasurementUnit.Points) / 72);
        int PageHeight = DPI * ((int)PDFPage1.GetHeight(PDFMeasurementUnit.Points) / 72);

        // Create a bitmap with the page's dimensions
        Bitmap Bitmap1 = new Bitmap(PageWidth, PageHeight);

        // Set the Graphics instance to an image
        Graphics1 = Graphics.FromImage(Bitmap1);

        // Make the Graphics instance suitable for rendering PDF content
        Graphics1.SmoothingMode = SmoothingMode.AntiAlias;
        Graphics1.PageUnit = GraphicsUnit.Point;
        Graphics1.PixelOffsetMode = PixelOffsetMode.HighQuality;
        Graphics1.TextRenderingHint = System.Drawing.Text.TextRenderingHint.AntiAlias;
        Graphics1.InterpolationMode = InterpolationMode.High;

        // Render page 3 on Graphics instance
        PDFDocument1.RenderOnGraphics(Graphics1, 3);
        PDFDocument1.Close();

        // Save rendered content to a bitmap image file
        Bitmap1.Save("sample_doc_page3.bmp", ImageFormat.Bmp);

        // Clean up
        Bitmap1.Dispose();
        Graphics1.Dispose();
        PDFDocument1.Dispose();

    }
}

RenderOnGraphics() used in the above code snippet will render content as is displayed on the screen by a viewer application. A PDF page may look different when it is printed on paper. If you wish to render on graphics to show a "Print Preview," then you need to use the other overload of the method that has a flag for rendering print output. Here is the method definition.

// In C#
public void RenderOnGraphics(
   Graphics g,
   int pageNum,
   bool printing
)

// In VB
Public Overloads Sub RenderOnGraphics( _
   ByVal g As Graphics, _
   ByVal pageNum As Integer, _
   ByVal printing As Boolean _
)

If you set the printing parameter to true and then call RenderOnGraphics(), then PDFDocument will not render form fields, annotations and other PDF page elements that are not meant to be printed.