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https://issues.apache.org/jira/browse/PDFBOX-2126?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14045190#comment-14045190
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Petr Slaby commented on PDFBOX-2126:
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Attached updated patch against latest trunk.
I have moved the intersection of current clipping path with new clipping into
PDGraphicsState#setCurrentClippingPath() to avoid duplicate code on places
where this method is called (a second call has been added in PDFBOX-1875 now).
There is a performance optimization in the computation of intersection trying
to avoid creation of Area wherever possible. I do not insist on that, but it
brought a big performance and memory consumption improvement on a corner case
PDF where a very complex clipping path is used. It brought also some one pixel
differences on a few of my test files, but I am not able to decide whether the
"before" or "after" is correct.
I am still hesitant to make the clip path immutable and private to the
PDGraphicsState as that would mean to make a clone of input in setClipPath()
and either a clone of output in getClipPath() or an introduction of methods
like applyClipping(Graphics2D) and fillClipPath(Graphics2D) in PDGraphicsState.
> Optimize clipping
> -----------------
>
> Key: PDFBOX-2126
> URL: https://issues.apache.org/jira/browse/PDFBOX-2126
> Project: PDFBox
> Issue Type: Improvement
> Components: Rendering
> Affects Versions: 2.0.0
> Reporter: Petr Slaby
> Attachments: ClipPath.1.patch, ClipPath.patch, example_010.pdf
>
>
> As already stated in a TODO comment in PageDrawer, the call of
> Graphics2D#setClip() is time and memory consuming. The attached patch
> optimizes clipping by calling Graphics2D#setClip() only if the clipping path
> has changed. The effect depends on the document, e.g. the attached one
> renders in 10.5s without the optimization and in 5.5 seconds in the optimized
> version.
> The clipping has to be re-applied whenever the transform in Graphics2D
> changes. This is not explicitly checked for, the implementation rather
> depends on the cached value being reset manually. Currently this is only
> needed at one place when processing annotations (AcroForms). Also, the
> implementation relies upon the clipping path object stored in PDGraphicsState
> to never change so that a comparison using == can be used. This works fine,
> but needs a bit of awareness in future changes. To make the design more
> clean, the clipping path could be made private to PDGraphcisState and thus
> really "immutable" from outside.
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