Home » Newsletter » November 2007

How To Set Transparency Levels For PDF Elements

Render text, shapes, and images in PDF with varying levels of transparency.

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 object
PdfWriter w = PdfWriter.fileWriter("TransparencyDemo.pdf");
PdfDocument d = new PdfDocument(w);

// Create a font object
PdfFont f = PdfFont.create(
                     "Helvetica",             // font name
                     PdfFont.STROKE_AND_FILL, // style 
                     30,                      // size  
                     PdfEncodings.WINANSI     // encoding
                          );

// Create an image object
PdfImage img = PdfImage.create("Logo.png");

// Create three pages
PdfPage p1 = new PdfPage();
PdfPage p2 = new PdfPage();
PdfPage p3 = new PdfPage();

String str = "This is transparent text";

int y = 0;
float transparency = 0.0f;
double imgPos = 0.0;

Color penColor = null;
Color brushColor = null;

// Set font size and color
f.setSize(30);
f.setColor(Color.magenta);

// Write transparent text on the three pages
p1.writeText(
     "Rendering Transparent Text", // text
     f,                            // font
     PdfTextFormatter.CENTER,      // alignment
     0,                            // x-coordinate
     50                            // y-coordinate 
           );
p2.writeText("Rendering Transparent Shapes", f,
            PdfTextFormatter.CENTER, 0, 50);
p3.writeText("Rendering Transparent Images", f,
            PdfTextFormatter.CENTER, 0, 50);

// Change font size and color
f.setColor(Color.green);
f.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 - transparency // alpha
                        );
 penColor = new Color(0.0f, 1.0f, 0.0f,
                      1.0f - transparency);

 // Set page 1's brush and pen colors
 p1.setBrushColor(brushColor);
 // p1.setPenColor(penColor); // You can uncomment this line

 // Write transparent text on page 1
 p1.writeText(str, f, PdfTextFormatter.CENTER, 
              0, 130 + y, true);

 // Set page 2's brush and pen colors
 p2.setBrushColor(brushColor);
 p2.setPenColor(penColor);

 // Draw transparent shapes on page 2
 p2.drawEllipse(150, 130 + y, 230, 160 + y, true, true);
 p2.drawSquare(300, 130 + y, 50, true, true);
 p2.drawCircle(450, 155 + y, 25, true, true);

 // Set page 3's brush color
 p3.setBrushColor(brushColor);
 // Pen settings not required when drawing images

 // Draw transparent images on page 3
 p3.drawImage(
      img,                               // image
      (p3.getWidth() - img.width())/2,   // x-coordinate
      130 + imgPos                       // y-coordinate
            );

 // Change positions for next iteration
 imgPos = imgPos + img.height() + 2;
 y += 60;

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

// Add pages to document
d.add(p1);
d.add(p2);
d.add(p3);

// Write file to disk and open it afterwards
d.setOpenAfterSave(true);
d.write();
w.dispose();

---oO0Oo---

Downloads:

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

This site is best viewed on a screen with minimum resolution of 1152 x 864 pixels. Windows users are advised to use Microsoft ClearType Tuning for optimal experience. Linux and other users can enable font smoothing, as supported by their OS. Also, please use the latest version of a standards-compliant browser such as Opera, FireFox, Chrome or Safari.