iText：仅当位置为空时才在PDF上显示图像 [英] iText : image on PDF only if the position is blank

问题描述

需要在特定位置的每个页面上绘制图像。限制是我们应该只在特定位置为空（不包含任何文本/图像/表等）时粘贴图像。有没有办法做到这一点？

Have an image that need to be painted on each page at a specific location. The constraint is we should paste the image only if the specific location is blank (not containing any text/images/tables, etc). Is there a way to do this?

推荐答案

是的，有。

1. 使用 IEventListener 来解析pdf中的特定页面。
   您将收到有关解析器在页面上处理的每个事件的通知。有3种。 PathRenderInfo ， TextRenderInfo ， ImageRenderInfo 。

1. Use IEventListener to parse a specific page in the pdf. You'll get notified about every event that the parser handles on the page. There are 3 kinds. PathRenderInfo, TextRenderInfo, ImageRenderInfo.

可以查询所有这些事件的内容坐标，以及在渲染之前应用的变换矩阵。

All of these events can be queried for the coordinates of their content, as well as the transformation matrix that is applied before rendering them.

这允许您计算在某个页面上呈现的内容占用的 Rectangle 。

This allows you to calculate the Rectangle that is occupied by the content that was rendered on a certain page.

现在您已拥有此矩形集合，您可以轻松检查给定矩形是否与这些矩形中的任何一个相交。 java.awt.Rectangle 有一个名为的方法相交

Now that you have this collection of Rectangles, you can easily check whether a given rectangle intersects with any of these rectangles. java.awt.Rectangle has a method for this called intersects

然后使用一些示例代码将图像定位在绝对位置。

Then use some of the example code to position an image at an absolute position.

这是星期五，对每个人来说都是美好的一天。所以这是代码;

It's Friday, which is a wonderful day for everyone. So here's the code;

class FreeSpaceFinder implements IEventListener
{

    private Collection<Rectangle> areas = new HashSet<>();

    public FreeSpaceFinder(PdfPage page)
    {
        areas.clear();
        PdfCanvasProcessor processor = new PdfCanvasProcessor(this);
        processor.processPageContent(page);
    }

    public Collection<Rectangle> getOccupiedAreas()
    {
        return areas;
    }

    @Override
    public void eventOccurred(IEventData iEventData, EventType eventType) {
        if(eventType == EventType.RENDER_TEXT)
            processText((TextRenderInfo) iEventData);
        else if(eventType == EventType.RENDER_PATH)
            processPath((PathRenderInfo) iEventData);
        else if(eventType == EventType.RENDER_IMAGE)
            processImage((ImageRenderInfo) iEventData);
    }

    private void processText(TextRenderInfo info)
    {
        for(TextRenderInfo characterRenderInfo : info.getCharacterRenderInfos())
        {
            com.itextpdf.kernel.geom.Rectangle charBoundingBox = new CharacterRenderInfo(characterRenderInfo).getBoundingBox();
            areas.add(new Rectangle(    (int) charBoundingBox.getX(),
                                        (int) charBoundingBox.getY(),
                                        (int) charBoundingBox.getWidth(),
                                        (int) charBoundingBox.getHeight()));
        }
    }

    private void processPath(PathRenderInfo info)
    {
        for(Subpath subpath : info.getPath().getSubpaths())
        {
            for(IShape segment : subpath.getSegments())
            {
                if(segment instanceof Line)
                {
                    processLine(info, (Line) segment);
                }
            }
        }
    }

    private float[] applyMtx(Matrix m, float[] point)
    {
        Matrix m2 = m.multiply(new Matrix(point[0], point[1]));
        return new float[]{m2.get(Matrix.I31), m2.get(Matrix.I32)};
    }

    private void processLine(PathRenderInfo info, Line shape)
    {

        float[] p0 = applyMtx(info.getCtm(), new float[]{(float) shape.getBasePoints().get(0).getX(), (float) shape.getBasePoints().get(0).getY()});
        int x0 = (int) p0[0];
        int y0 = (int) p0[1];

        float[] p1 = applyMtx(info.getCtm(), new float[]{(float) shape.getBasePoints().get(1).getX(), (float) shape.getBasePoints().get(1).getY()});
        int x1 = (int) p1[0];
        int y1 = (int) p1[1];

        int w = java.lang.Math.abs(x0 - x1);
        int h = java.lang.Math.abs(y0 - y1);

        areas.add(new Rectangle(java.lang.Math.min(x0,x1), java.lang.Math.min(y0,y1), java.lang.Math.max(w, 1), java.lang.Math.max(h, 1)));
    }

    private void processImage(ImageRenderInfo info)
    {
        // #TODO
    }

    @Override
    public Set<EventType> getSupportedEvents() {
        return null;
    }
}

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