java - 文本位置边界框 PDFBox

Question

我正在尝试从 TextPosition 绘制相应的字形边界框，如 PDF 32000 文档中所示。

这是我的函数，它执行从字形空间到用户空间的计算

@Override 
protected void processTextPosition(TextPosition text) {
    PDFont font = pos.getFont();
    
    BoundingBox bbox = font.getBoundingBox();
    
    Rectangle2D.Float rect = new Rectangle2D.Float(bbox.getLowerLeftX(), bbox.getUpperRightY(), 
            bbox.getWidth(), bbox.getHeight());
    
    AffineTransform at = pos.getTextMatrix().createAffineTransform();
    
    if (font instanceof PDType3Font) {
        at.concatenate(font.getFontMatrix().createAffineTransform());
    } else {
        at.scale(1 / 1000f, 1 / 1000f);
    }
    Shape shape = at.createTransformedShape(rect);
    rectangles.add(fillBBox(text));
    
            
    super.processTextPosition(text);
}

这是绘制提取的矩形的函数:

private void drawBoundingBoxes() throws IOException {
    
    String fileNameOut = path.substring(0, path.lastIndexOf(".")) + "_OUT.pdf";
    log.info("Drawing Bounding Boxes for TextPositions");
    
    PDPageContentStream contentStream = new PDPageContentStream(document, 
            document.getPage(document.getNumberOfPages()-1),
            PDPageContentStream.AppendMode.APPEND, false , true );
    contentStream.setLineWidth(1f);
    contentStream.setStrokingColor(Color.RED);
    
    try{
        for (Shape p : rectangles) {
            p = all.get(0);
        double[] coords = new double[6];
        GeneralPath g = new GeneralPath(p.getBounds2D());
        for (PathIterator pi = g.getPathIterator(null);
             !pi.isDone();
             pi.next()) {
            System.out.println(Arrays.toString(coords));
            switch (pi.currentSegment(coords)) {
            case PathIterator.SEG_MOVETO:
                System.out.println("move to");
                contentStream.moveTo ((float)coords[0], (float) coords[1]);
                break;
                
            case PathIterator.SEG_LINETO:
                System.out.println("line to");
                contentStream.lineTo ((float)coords[0], (float) coords[1]);
                break;
                
            case PathIterator.SEG_CUBICTO:
                System.out.println("cubc to");
                contentStream.curveTo((float)coords[0], (float) coords[1],
                        (float)coords[2], (float) coords[3], 
                        (float)coords[4],(float) coords[5]);
                break;
                
            case PathIterator.SEG_CLOSE:
                System.out.println("close");
                contentStream.closeAndStroke();
                break;
            default:
                System.out.println("no shatt");
                break;
            }
            
        }
    
    } catch (Exception e) {
        e.printStackTrace();
    } finally {
        contentStream.close();
        document.save(new File(fileNameOut));
    }
}

然后，当我尝试在 pdf 上绘图时，我得到第一个字母(大写 V)的以下结果

我不知道我做错了什么。有什么想法吗？

Answer 1

先生。 D、

我测试了你的代码，让它工作所需的唯一改变就是反转 Y 轴。需要这样做的原因是 PDF 用户空间 中的原点位于左下角，而 Java 2D 用户空间 的原点位于左上角^[1]。

8.3.2.3 User Space

The user space coordinate system shall be initialized to a default state for each page of a document. The CropBox entry in the page dictionary shall specify the rectangle of user space corresponding to the visible area of the intended output medium (display window or printed page). The positive x axis extends horizontally to the right and the positive y axis vertically upward, as in standard mathematical practice (subject to alteration by the Rotate entry in the page dictionary). The length of a unit along both the x and y axes is set by the UserUnit entry (PDF 1.6) in the page dictionary (see Table 30). If that entry is not present or supported, the default value of 1⁄72 inch is used. This coordinate system is called default user space.^[2]

源代码

@Override 
protected void processTextPosition(TextPosition text) {
    try {
        PDFont font = pos.getFont();

        BoundingBox bbox = font.getBoundingBox();

        Rectangle2D.Float rect = new Rectangle2D.Float(bbox.getLowerLeftX(), bbox.getUpperRightY(),
                    bbox.getWidth(), bbox.getHeight());

        AffineTransform at = pos.getTextMatrix().createAffineTransform();

        if (font instanceof PDType3Font) {
            at.concatenate(font.getFontMatrix().createAffineTransform());
        } else {
            at.scale(1 / 1000f, 1 / 1000f);
        }

        Shape shape = at.createTransformedShape(rect);

        // Invert Y axis
        Rectangle2D bounds = shape.getBounds2D();
        bounds.setRect(bounds.getX(), bounds.getY() - bounds.getHeight(), bounds.getWidth(), bounds.getHeight());

        rectangles.add(bounds);

        super.processTextPosition(text);

    } catch (IOException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }
}

引用文献

1. Java 2D API Concepts: Coordinates

2. 文档管理 - 可移植文档格式 - 第 1 部分:PDF 1.7，PDF 32000-1:2008 ，第 8.3 节:坐标系，第 115 页