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

Question

我使用的示例基于

中的 TransparentWatermark 示例

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

但我似乎找不到与 Adob​​e 设置中的方法或选项相关的方法或选项，其中包含为 "Scale Relative to target page" 添加水印。

有人可以指点我吗？

Answer 1

尝试创建一个 Textwatermark 示例的变体，它可以缩放水印以覆盖整个页面区域的一定百分比。本质上，这是找到正确的缩放变换并确保所有其他平移和旋转正确的线性代数问题

package Whosebug.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/Whosebug/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;

        }
    }
}