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https://issues.apache.org/jira/browse/PDFBOX-2126?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14049061#comment-14049061
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Tilman Hausherr commented on PDFBOX-2126:
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Look at the difference between the two PNG files. It is sometimes hard to see
especially if your monitor is very "white". One different shape is at the
bottom left, at the right of the small rectangle.
> 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, PDFBOX-1772.pdf,
> PDFBOX-1772.pdf-1-bad.png, example_010.pdf, pdfbox-1772.pdf-1-good.png
>
>
> 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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