[jira] [Created] (PDFBOX-2126) Optimize clipping

["Petr Slaby (JIRA)" <ji...@apache.org>]

Petr Slaby created PDFBOX-2126:
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             Summary: 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


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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