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.
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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