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Home » Newsletter » November 2007

By Lokesh Vardhan Yadav .G and Santhanam L.

In this article, you will learn how to specify transparency levels for PDF elements such as text, shapes, and images.*

To render the above-mentioned PDF elements, PDFOne Java uses a pen and a brush. The pen is used to stroke text and shapes. The brush is used to fill text and shapes.

You can set the color for the pen and brush of a PDF page (PdfPage) or a PDF document (PdfDocument) object.

After you set a color for the pen and brush, PDF elements that you render on a page or document will be stroked and filled using that color.

While specifying a color for the pen and brush, you can also include an alpha value that would affect the transparency level with which the coloring operations of the pen and brush are performed.

This is how semi-transparent text and shapes are rendered. When rendering semi-transparent images, however, the alpha value of the color of the brush alone is used. The pen setting plays no role here.

Finally, here is a code snippet that shows how to render text, shapes and images with varying levels of transparency.

// Create a PDF document
PdfDocument doc = new PdfDocument();

try {
  // Create a Helvetica font instance
  PdfFont fontHelvetica;
  fontHelvetica = 
    PdfFont.create("Helvetica",             // font name
                   PdfFont.STROKE_AND_FILL, // pen and brush style
                   30,                      // size
                   PdfEncodings.WINANSI);   // encoding
  // Set font size and color
  fontHelvetica.setSize(30);
  fontHelvetica.setColor(Color.magenta);

  // Create an image instance
  PdfImage logoImage = PdfImage.create("logo.png");

  // Create three pages
  PdfPage page1 = new PdfPage();
  PdfPage page2 = new PdfPage();
  PdfPage page3 = new PdfPage();

  String transparentText = "This text is transparent.";

  int verticalOffset = 0;
  float transparencyChange = 0.0f;
  double imageVerticalOffset = 0.0;

  Color penColor = null;
  Color brushColor = null;

  // Write transparent text on the three pages
  page1.writeText("Rendering Transparent Text", // text
                  fontHelvetica,                // font
                  PdfTextFormatter.CENTER,      // alignment
                  0,                            // x-coordinate
                  50);                          // y-coordinate
  page2.writeText("Rendering Transparent Shapes", 
                  fontHelvetica,
                  PdfTextFormatter.CENTER, 
                  0, 50);
  page3.writeText("Rendering Transparent Images", 
                  fontHelvetica,
                  PdfTextFormatter.CENTER, 
                  0, 50);

  // Change font size and color
  fontHelvetica.setColor(Color.green);
  fontHelvetica.setSize(30);

  for (int i = 0; i < 5; i++) {
    // Create new brush and pen color
    brushColor = new Color(1.0f,                  // red
                           1.0f,                  // green
                           0.0f,                  // blue
                           1.0f - transparencyChange);  // alpha
    penColor = new Color(0.0f, 1.0f, 0.0f, 1.0f - transparencyChange);
   
    // Set brush and pen colors of page 1
    page1.setBrushColor(brushColor);
    page1.setPenColor(penColor); 
   
    // Write transparent text on page 1
    page1.writeText(
      transparentText, 
      fontHelvetica, 
      PdfTextFormatter.CENTER, 
      0, 
      130 + verticalOffset, 
      true);
   
    // Set brush and pen colors of page 2
    page2.setBrushColor(brushColor);
    page2.setPenColor(penColor);
     
    // Draw transparent shapes on page 2
    page2.drawEllipse(150, 130 + verticalOffset, 230, 160 + verticalOffset, true, true);
    page2.drawSquare(300, 130 + verticalOffset, 50, true, true);
    page2.drawCircle(450, 155 + verticalOffset, 25, true, true);
     
    // Set brush color of page 3
    page3.setBrushColor(brushColor);
    // Pen settings not required when drawing filled images
     
    // Draw transparent images on page 3
    page3.drawImage(
      logoImage,                  // image
      (page3.getWidth() -         // x-coordinate
        logoImage.width())/2, 
      130 + imageVerticalOffset); // y-coordinate

    // Change offsets for next iteration
    imageVerticalOffset = imageVerticalOffset + logoImage.height() + 2;
    verticalOffset += 60;

    // Change transparency level for next iteration
    transparencyChange += 0.2f;
  }

  // Add the pages to the document
  doc.add(page1);
  doc.add(page2);
  doc.add(page3);

  // Save the document to file
  doc.save("TransparencyDemo.pdf");
  doc.close();
} catch (IOException | PdfException e) {
  // TODO Auto-generated catch block
  e.printStackTrace();
}

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Downloads:

• PDF document with transparent text, shapes, and images.
• Java source code

* - This article is a PDFOne Java version of an earlier article written in March 2007 for our PDFOne .NET users.