Details
New Feature
Major
Description
Steps to reproduce:
1) Open sample PDF doc in Viewer RI and show the utility pane
2) Select any of the graphical tools (Line, Rectangle, Circle, or Ink Annotation)
3) Create an annotation anywhere on the page, and select it
4) Change line/border/ink color for the selected annotation, specifying alpha value less than 255: http://i.imgur.com/WeKkx5k.png
Expected behavior:
Annotation line/border/ink becomes partially transparent: http://i.imgur.com/oL4EeiX.png (mocked up).
Actual behavior:
Annotation line/border/ink remains fully opaque: http://i.imgur.com/KP1cBjD.png
Additional info:
Expected behavior is possible to achieve programmatically by extending SquareAnnotationHandler and setting lineColor field to a Color object with partial alpha.
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Hmm. Digging deeper into this, I see that PDF spec does not permit RGBA values for Annotation color ("C" key). So the behavior in Annotation.setColor(...) is correct. I guess my only option to get transparent annotations is to define an AppearanceStream for my annotations. I'll have to take a look at how "fillColor" is handled (which does appear to support transparency/RGBA), and try to emulate it.
So – instead of a bug report, consider this a feature request: allow RGBA colors to be used for Annotation.setColor(...)
As you already researched the PDF colour mechanism doesn't support alpha. Alpha values are defined using an external graphics context. It would take a bit of work but it could be added as an enhancement for out annotation tools. I'll update this bug to reflect the enhancement request.
Marking as fixed.
Actually, it seems that the problem is in Annotation.setColor(...) rather than in the Viewer RI code. The first line of this method copies just the RGB components, and discards the alpha channel. So I was incorrect – it's not possible to work around this by extending AnnotationHandlers, since that would only fix the tool appearance, and not appearance of the actual annotation.