Re: Alpha blending details?

[Philipp K. J. <ja...@ie...>]

On Sat, 06 Dec 2014 22:22:38 -0800
sfeam <sf...@us...> wrote:

> On Saturday, 06 December 2014 08:40:19 AM Philipp K. Janert wrote:
> > 
> > What blending mode or operator does gnuplot
> > use for alpha blending?
> > 
> > According to this page, there are many possible
> > choices:
> > 	http://cairographics.org/operators/
> > 
> > Based on some tests, possible options seem to be 
> > OPERATOR_OVER, OPERATOR_ADD, and OPERATOR_SATURATE.
> > 
> > Does anyone know?
> 
> Polygons are drawn with
> cairo_set_operator(context,CAIRO_OPERATOR_SATURATE);
> 
> I don't see any separate set operation for RGBA lines.  They are
> drawn with cairo_set_source_rgba() but I do not know if that means
> they end up using the default operator (OVER) or whether the SATURATE
> operator carries over from some previous fill_polygon() operation, if
> any.

Thanks!

	Ph.