在中心 Apache PDFBox 上以 45 度角旋转水印文本 [英] Rotate watermark text at 45 degree angle across the center Apache PDFBox

问题描述

我想使用 PDFBox API 将文本添加到 PDF 并将其旋转 45 度并将其放置在页面的中心，文本是动态的，应该始终放置在中心，我可以完成其他所有工作除了居中件，我将不胜感激任何帮助.我有这个代码:

I want to add a text to the PDF using PDFBox API and rotate it by 45 Degree and place it at the center of the page, The text is dynamic and should be placed in the center always, I got everything else to work except centering piece, I'll appreciate any help. I have this code:

Point2D.Float pageCenter = getCenter(page);

float stringWidth = getStringWidth(watermarkText, font, fontSize);
float textX = pageCenter.x - stringWidth / 2F + center.x;
System.out.println(textX);
float textY = pageCenter.y + center.y;
//System.out.println("Inside cross"+textX+", "+textY);
fontSize = 110.0f;  
cs.transform(Matrix.getRotateInstance(Math.toRadians(45), textX, textY));
cs.moveTo(0, 0);
cs.lineTo(125, 0);
r0.setNonStrokingAlphaConstant(0.20f);

这是我想要的结果:输出PDF

推荐答案

我做的是首先根据计算出的角度进行旋转.在这个旋转的世界"中我做了一个水平偏移，使文本位于中间，并将文本垂直移动一点，使其位于垂直"位置.想象的对角线的中间(旋转世界"中的水平线).

What I do is to first rotate based on the calculated angle. In this "rotated world" I do a horizontal offset so that the text is in the middle, and also move the text vertically a bit lower, so that it is in the "vertical" middle of an imagined diagonal line (horizontal in the "rotated world").

try (PDDocument doc = new PDDocument())
{
    PDPage page = new PDPage();
    doc.addPage(page);

    PDFont font = PDType1Font.HELVETICA_BOLD;
    try (PDPageContentStream cs =
            new PDPageContentStream(doc, page, PDPageContentStream.AppendMode.APPEND, true, true))
        // use this long constructor when working on existing PDFs
    {
        float fontHeight = 110;
        String text = "Watermark";

        float width = page.getMediaBox().getWidth();
        float height = page.getMediaBox().getHeight();
        int rotation = page.getRotation();
        switch (rotation)
        {
            case 90:
                width = page.getMediaBox().getHeight();
                height = page.getMediaBox().getWidth();
                cs.transform(Matrix.getRotateInstance(Math.toRadians(90), height, 0));
                break;
            case 180:
                cs.transform(Matrix.getRotateInstance(Math.toRadians(180), width, height));
                break;
            case 270:
                width = page.getMediaBox().getHeight();
                height = page.getMediaBox().getWidth();
                cs.transform(Matrix.getRotateInstance(Math.toRadians(270), 0, width));
                break;
            default:
                break;
        }
        float stringWidth = font.getStringWidth(text) / 1000 * fontHeight;
        float diagonalLength = (float) Math.sqrt(width * width + height * height);
        float angle = (float) Math.atan2(height, width);
        float x = (diagonalLength - stringWidth) / 2; // "horizontal" position in rotated world
        float y = -fontHeight / 4; // 4 is a trial-and-error thing, this lowers the text a bit
        cs.transform(Matrix.getRotateInstance(angle, 0, 0));
        cs.setFont(font, fontHeight);
        //cs.setRenderingMode(RenderingMode.STROKE); // for "hollow" effect
        
        PDExtendedGraphicsState gs = new PDExtendedGraphicsState();
        gs.setNonStrokingAlphaConstant(0.2f);
        gs.setStrokingAlphaConstant(0.2f);
        gs.setBlendMode(BlendMode.MULTIPLY);
        cs.setGraphicsStateParameters(gs);
        
        // some API weirdness here. When int, range is 0..255.
        // when float, this would be 0..1f
        cs.setNonStrokingColor(255, 0, 0);
        cs.setStrokingColor(255, 0, 0);

        cs.beginText();
        cs.newLineAtOffset(x, y);
        cs.showText(text);
        cs.endText();
    }
    doc.save("watermarked.pdf");
}

请注意，我设置了描边和非描边(= 填充).这对于想要尝试(残疾人)空心"的人很有用.外观，那只用抚摸.默认模式是填充，即非描边.

Note that I've set both stroking and non stroking (= fill). This is useful for people who want to try the (disabled) "hollow" appearance, that one uses stroking only. The default mode is fill, i.e. non-stroking.

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