[Qgis-developer] Blend modes for printer/pdf outputs - advice?

[Nathan Woodrow]

I think option 2 is the best here but don't just warn the user let them
pick it from the message box.

So something like:

You have blend modes enabled but we can't print them as vectors.  What do
you want to do?

Enable Print as Raster | Print as Vector | Cancel

When someone pressing Enable Print as Raster it should tick the box and
print from there.

- Nathan



On Fri, May 3, 2013 at 9:57 AM, Nyall Dawson <nyall.dawson at gmail.com> wrote:

> Hi all,
>
> I'm after some advice on the best way to handle pdf or printer output
> of compositions when the composition or map contains blending.
>
> Since QPrinter doesn't support the QPainter composition modes, any
> blending options are currently ignored when exporting a composition to
> pdf/printer. There's two options I can see to handle this, and I'm
> wondering what everyone thinks is the best approach.
>
> Option 1 - Automatically export compositions with blending using rasters.
> This approach would check whether the composition contains any
> blending, and if so would use the "print as raster" option to
> effectively flatten the output before exporting. This is probably the
> most user-friendly approach, since the user doesn't need to do
> anything extra to get the printout looking correct.
>
> Option 2 - Warn the user that blending requires 'print as raster' checked
> This approach would display a warning dialog when attempting to
> print/pdf a composition containing blending (similar to how svg
> outputs currently show a warning). The warning would tell the user to
> check "print as raster" if they want the blending modes used in the
> export.
>
> The advantage with option 2 is that it leaves the possibility for
> vector-based exports even when blending has been used. This way, a
> user who wants to further edit a composition in a vector illustration
> program (inkscape/illustrator/etc) can still export to an editable pdf
> to tweak the map and re-apply the blending in the external program.
> Option 1 would make this impossible, since any blending would force
> the output into raster format and prevent any manual editing of the
> composition.
>
> For this reason my gut feeling is that option 2 is a better way to go,
> but I thought I'd raise it with the list for other opinions.
>
> Nyall
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