[Qgis-user] Blending layers question

[Andreas Neumann]

Hi Matt,

QGIS uses blend modes baked into qtpainter. So the qt library is 
providing these blend modes. You would have to dig into the qt source 
code to find out details. See 
http://doc.qt.io/qt-4.8/qpainter.html#CompositionMode-enum for a starter.

But I would assume that blend modes are well covered in computer 
graphics literature and you could google some papers. They have been 
around for many years now.

Andreas

On 10.09.2015 04:02, Matt Boyd wrote:
> Thanks Nicolas,
> yes, I'm aware of those properties. What I'm trying to work out is how 
> QGIS does this so I can use it outside of QGIS in another program. 
> Some pointers to the sort of questions I should be asking google on 
> transparency would be handy.
>
> Thanks
>
> On Thu, Sep 10, 2015 at 10:33 AM, Nicolas Cadieux 
> <nicolas.cadieux at archeotec.ca <mailto:nicolas.cadieux at archeotec.ca>> 
> wrote:
>
>     Hi,
>
>     In your raster properties, you can render layers using various
>     methods like add, multiply...  It works very well.  Same options
>     are available for vector layer and objects.
>
>     Nicolas Cadieux M.Sc.
>     Les Entreprises Archéotec inc.
>     8548, rue Saint-Denis Montréal H2P 2H2
>     Téléphone: 514.381.5112 <tel:514.381.5112>  Fax: 514.381.4995
>     <tel:514.381.4995>
>     www.archeotec.ca <http://www.archeotec.ca>
>
>     On Sep 9, 2015 7:51 PM, "Matt Boyd [via OSGeo.org]" <[hidden
>     email] <http:///user/SendEmail.jtp?type=node&node=5223435&i=0>> wrote:
>
>         Hi Group,
>         this is possibly one of those questions about a question. I'd
>         like to create some blended layers that look the same as
>         layers in QGIS with transparency applied.
>         I've another application that my data lives in and they supply
>         a calculator that's able to do some fairly reasonable maths on
>         different grids and other types of data.
>
>         How does QGIS do transparency, and can I use those equations /
>         method elsewhere.
>
>         Thanks
>         Matt
>
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