Re: Alpha blending details?

[sfeam <sf...@us...>]

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.

	Ethan