[XaraXtreme-dev] Export preview & ImageMagick

[Alex Bligh <alex@xxxxxxxxxxx>]

When using ImageMagick to export, there will be no way of doing an
accurate preview without exporting the entire file and reimporting
it (i.e. writing the thing to disk). This could potentially be
time consuming, and may not be possible (for instance some ImageMagick
filters are write-only, and some we are only implementing in a
write-only manner).

We thus have three options
a) Do not show export preview at all
   - Advantage: easy
   - Disadvantage: no preview
b) Show the intermediate PNG as the export preview
   - Advantage: you get to see the resolution, plus things like
                transparency, correctly
                should be easy to code (the same as the PNG
                filter)
   - Disadvantage: it may be misleading, for instance if the
     filter converts the PNG to black and white, ignores the
     transparency, etc.
c) Attempt "best effort" to display an accurate preview, by
   saving the file out, and if the same filter also does
   reads, reading it in again; if not either use the PNG
   as a preview or disable preview totally.
   - Advantage: most accurate preview
   - Disadvantage: hardest & most time-consuming to code
                   highest potential of going wrong (especially
                   at an "interactive" stage)
                   may be slow in practice

Views?

I'm not planning on working on this till Luke's finished his
stuff (i.e. post 0.7).

Alex