Am 07.09.2016 um 16:00 schrieb Markus Barbey:
Hello there,
I'm using PDFBox version 2.0.2 and I'm just struggling with the
PDFRenderer#renderPageToGraphics (int, Graphics2D)
implementation, which triggers the
PageDrawer#drawImage (PDImage) throws IOException
for image drawing. The PDImage instance is holding an image soft reference, once the image has been resolved.
When calling
PDFRenderer#renderPageToGraphics (int, Graphics2D)
multiple times for the same renderer instance, the
PageDrawer#drawImage (PDImage) throws IOException
gets always called with a freshly generated PDImage instance (which has not yet a cached image to use). Therefore the image gets extracted from the PDF stream anew, although it has already been cached in the previously used PDImage instance.
The PDImageXObject should be cached thanks to the document wide cache
referenced in PDResources.
I haven't tested your observation yet; the only explanation for now
would be that your PDF was just created, i.e. not read from a file or a
stream. (Thus no COSObject references)
Tilman
As a workaround I created my own PDFRender implementation, that uses a dedicated and reused PageDrawer for a visible PDF page. Then I created my own implementation for PageDrawer, that is holding PDImage references, that can be reused. Instead of drawing the freshly generated PDImage, I lookup the first generated one.
private class CacheablePageDrawer
extends PageDrawer {
public CacheablePageDrawer (PageDrawerParameters pParameters)
throws IOException {
super (pParameters);
}
/** the image cache */
Map <COSStream, PDImage> fPDImageCache = new HashMap <COSStream,
PDImage> ();
@Override
public void drawImage (PDImage pPdImage) throws IOException
{
PDImage vPDImageToDraw = pPdImage;
if (pPdImage instanceof PDImageXObject) {
PDImageXObject vPDImageXObject = (PDImageXObject) pPdImage;
COSStream vCOSStream = vPDImageXObject.getCOSObject ();
if (!fPDImageCache.containsKey (vCOSStream)) {
fPDImageCache.put (vCOSStream,
pPdImage);
}
vPDImageToDraw = fPDImageCache.get (vCOSStream);
}
super.drawImage (vPDImageToDraw);
}
}
Although it works, it does not seem to be meant to be use that way. So I'm wondering, if there is a better solution to get the image caching to work on multiple renderPageToGraphics(...) calls?
Thanks,
Markus
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