How do I get background data from pptx slides using apache poi

Question

I am trying to build a rather crude tool that converts a ppt/pptx file to a HTML format.
I have found out that, unfortunately, apache poi does not provide a unified programming model for working with power point files and code has to be written for parsing each format.
I feel that the pptx file support is much more limited than the ppt support. One problem I'm facing is getting information regarding the background (color, pattern, background image) of a pptx slide.

I find the XSLFBackground (pptx api) class to be much more limited than its corresponding Background class (ppt api).
Has anyone managed to get get information regarding the background of a pptx slide using apache poi ?

Also can someone please point me to some good resources on this subject. I find the apache poi javadoc almost unusable and the examples on the poi website only cover basic functionality.

Best regards, Sergiu

Answer 1

The content of the background element is described in the Office Open Schema - check the zip-link at the bottom and the pml-slide.xsd inside.

With the schema in the hand you will understand the XML beans below the usermodel interface.

For a starter, here is an example of reading a background image and also of exporting the slides to pngs (maybe useful for your html export?):

import java.awt.*;
import java.awt.geom.*;
import java.awt.image.BufferedImage;
import java.io.*;
import java.net.URL;
import org.apache.poi.xslf.usermodel.*;
import org.openxmlformats.schemas.presentationml.x2006.main.CTBackground;

public class PptxBackground {
    public static void main(String[] args) throws Exception {
        // sorry for the content, but it was one of the first non-commercial google matches ... 
        URL url = new URL("http://newkilpatrickblog.typepad.com/files/sunday_june_03_2012_trinity_and_majesty_communion.pptx");
        InputStream is = url.openStream();
        XMLSlideShow ss = new XMLSlideShow(is);
        is.close();

        XSLFSlide sld = ss.getSlides()[0];
        XSLFBackground bg = sld.getBackground();
        CTBackground xmlBg = (CTBackground)bg.getXmlObject();
        String relId = xmlBg.getBgPr().getBlipFill().getBlip().getEmbed();

        XSLFPictureData pic = (XSLFPictureData)sld.getRelationById(relId);
        String filename = pic.getFileName();
        byte fileBytes[] = pic.getData();


        /***** or convert the slides to images ****/

        double zoom = 2; // magnify it by 2
        AffineTransform at = new AffineTransform();
        at.setToScale(zoom, zoom);

        Dimension pgsize = ss.getPageSize();
        XSLFSlide slides[] = ss.getSlides();
        for (int i = 0; i < slides.length; i++) {
            BufferedImage img = new BufferedImage((int)Math.ceil(pgsize.width*zoom), (int)Math.ceil(pgsize.height*zoom), BufferedImage.TYPE_INT_RGB);
            Graphics2D graphics = img.createGraphics();
            graphics.setTransform(at);          

            graphics.setPaint(Color.white);
            graphics.fill(new Rectangle2D.Float(0, 0, pgsize.width, pgsize.height));
            slides[i].draw(graphics);
            FileOutputStream out = new FileOutputStream("slide-"  + (i+1) + ".png");
            javax.imageio.ImageIO.write(img, "png", out);
            out.close();        
        }
    }
}