如何在 PDF 中添加水印并使用"Scale Relative to target Page"

Question

我正在使用一个基于透明水印示例

的示例http://developers.itextpdf.com/examples/stamping-content-existing-pdfs/clone-watermark-examples

但我似乎找不到与 Adobe 设置中带有"相对于目标页面缩放"添加水印的方法或选项相关的方法或选项。

有人可以指出我吗？

Answer 1

尝试创建文本水印示例的变体，该变体缩放水印以覆盖总页面区域的百分比。从本质上讲，这是一个线性代数问题，需要找到正确的缩放转换并确保所有其他平移和旋转都是正确的

。

package Stackoverflow.ScalingWatermark;
import com.itextpdf.io.IOException;
import com.itextpdf.io.font.FontConstants;
import com.itextpdf.kernel.color.Color;
import com.itextpdf.kernel.color.DeviceCmyk;
import com.itextpdf.kernel.events.Event;
import com.itextpdf.kernel.events.IEventHandler;
import com.itextpdf.kernel.events.PdfDocumentEvent;
import com.itextpdf.kernel.font.PdfFont;
import com.itextpdf.kernel.font.PdfFontFactory;
import com.itextpdf.kernel.geom.AffineTransform;
import com.itextpdf.kernel.geom.Rectangle;
import com.itextpdf.kernel.pdf.PdfDocument;
import com.itextpdf.kernel.pdf.PdfPage;
import com.itextpdf.kernel.pdf.PdfWriter;
import com.itextpdf.kernel.pdf.canvas.PdfCanvas;
import com.itextpdf.kernel.pdf.xobject.PdfFormXObject;
import com.itextpdf.layout.Document;
import com.itextpdf.layout.border.SolidBorder;
import com.itextpdf.layout.element.AreaBreak;
import com.itextpdf.layout.element.Div;
import com.itextpdf.layout.element.Paragraph;
import com.itextpdf.layout.property.AreaBreakType;
import com.itextpdf.licensekey.LicenseKey;
import java.io.File;
public class ScalingWatermark {
public static String DEST = "target/output/Stackoverflow/ScalingWatermark/output.pdf";
public static String LICENSE = "src/test/resources/skeleton-itextkey.xml";
public static String[] CONTENT = {"I have seen the face of sorrow", "She looks away in the distance",
"Across all these bridges", "From whence I came",
"And those spans, trussed and arched", "Hold up our lives as we go back again",
"To how we thought then", "To how we thought we thought then",
"I have seen sorrow's face", "But she is ever turned away",
"And her words leave me blind", "Her eyes make me mute",
"I do not understand what she says to me", "I do not know if to obey",
"Or attempt a flood of tears", "I have seen her face",
"She does not speak", "She does not weep",
"She does not know me", "For I am but a stone fitted in place",
"On the bridge where she walks", "―Lay of the Bridgeburners",
"Toc the Younger"
};
public static void main(String[] args) throws IOException, java.io.IOException {
LicenseKey.loadLicenseFile(LICENSE);
File file = new File(DEST);
file.getParentFile().mkdirs();
new ScalingWatermark().createPdf(DEST);
}
public void createPdf(String dest) throws IOException, java.io.IOException {
PdfWriter writer = new PdfWriter(dest);
PdfDocument pdfDoc = new PdfDocument(writer);
Document doc = new Document(pdfDoc);
pdfDoc.addEventHandler(PdfDocumentEvent.END_PAGE,
new TextWatermark());
addContent(doc);
doc.add(new AreaBreak(AreaBreakType.NEXT_PAGE));
addContent(doc);
doc.close();
}
private void addContent(Document doc) {
Div div = new Div().setBorder(new SolidBorder(1));
for (String line : CONTENT) {
Paragraph p = new Paragraph(line).setMarginBottom(0).setMarginTop(0).setMarginLeft(5f);
div.add(p);
}
doc.add(div);
}

protected class TextWatermark implements IEventHandler {
Color lime, blue;
PdfFont helvetica;
protected TextWatermark() throws java.io.IOException {
helvetica = PdfFontFactory.createFont(FontConstants.HELVETICA);
lime = new DeviceCmyk(0.208f, 0, 0.584f, 0);
blue = new DeviceCmyk(0.445f, 0.0546f, 0, 0.0667f);
}
@Override
public void handleEvent(Event event) {
PdfDocumentEvent docEvent = (PdfDocumentEvent) event;
PdfDocument pdf = docEvent.getDocument();
PdfPage page = docEvent.getPage();
int pageNumber = pdf.getPageNumber(page);
Rectangle pageSize = page.getPageSize();
//Scale to a percentage of the page area
float scalingAreaReq = pageNumber % 2 == 0 ? 0.75f : 0.50f;
//Calculate scaling and x-y positioning
float scalingFactor = (float) Math.sqrt(scalingAreaReq);
AffineTransform scaleTf = new AffineTransform();
//Calculation based on centering the watermark
float xPos = ((1 - scalingFactor) * pageSize.getWidth()) / 2;
float yPos = ((1 - scalingFactor) * pageSize.getHeight()) / 2;
//Add translation to our transformation
scaleTf.translate(xPos,yPos);
//Add scaling to our transformation
scaleTf.scale(scalingFactor, scalingFactor);
//Use values from calculation
PdfCanvas pdfCanvas = new PdfCanvas(page.newContentStreamBefore(), page.getResources(), pdf);
PdfFormXObject watermarkAsXObject = createWatermarkXObject(pageNumber, pageSize, pdf);
pdfCanvas.saveState()
//Apply scaling
.concatMatrix(scaleTf)
//Insert watermark
.addXObject(watermarkAsXObject, 0, 0)
.restoreState();
pdfCanvas.release();
}

private PdfFormXObject createWatermarkXObject(int pageNumber, Rectangle bBox, PdfDocument pdfDoc) {
PdfFormXObject xObject = new PdfFormXObject(bBox);
PdfCanvas pdfCanvas = new PdfCanvas(xObject, pdfDoc);
int fontSize = 40;
float margin = 100;
//Paint the area that the watermark occupies
pdfCanvas.saveState()
.setFillColor(pageNumber % 2 == 1 ? lime : blue)
.rectangle(bBox.getLeft(), bBox.getBottom(),
bBox.getWidth(), bBox.getHeight())
.fill().restoreState();
//Translation and rotation to center the watermark text
AffineTransform rotationAndTranslation = AffineTransform.getTranslateInstance(bBox.getWidth()/2- margin,bBox.getHeight()/2);
AffineTransform rotation = AffineTransform.getRotateInstance(Math.PI/4);
rotationAndTranslation.concatenate(rotation);
//Create the actual text
pdfCanvas.saveState()
.beginText()
.setFontAndSize(helvetica, fontSize)
.setFillColor(pageNumber % 2 != 1 ? lime : blue)
.setTextMatrix(rotationAndTranslation)
.showText("Watermark")
.endText()
.restoreState();
pdfCanvas.release();
return xObject;
}
}
}