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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