[poppler] Supporting PDF 1.6 UserUnit

[Kristian Høgsberg]

Leonard Rosenthol wrote:
> At 12:10 PM 7/11/2005, Kristian Høgsberg wrote:
> 
>> Did you try the PDFs in the bugs I mentioned?
> 
> 
>         No, I didn't.
> 
>         Where is the Poppler bug database kept?

It's on bugs.freedesktop.org, specifically:

   https://bugs.freedesktop.org/show_bug.cgi?id=3020
   https://bugs.freedesktop.org/show_bug.cgi?id=3098

and xpdf doesn't support those features either.  The image + image mask 
is difficult to support in the splash backend, because it scaleds and 
rotates the bitmap as it loads it.  Loading, scaling and rotating 
another bitmaps (the mask) in parallel with loading the image would be 
even more tricky than the current code, and performance would probably 
be horrible (you'd have to seek back and forth in the file for each pixel)

The alpha masks is also difficult to implement with the current splash 
backend, since it doesn't support alpha channels and compositing.

Kristian