[cairo] composites circle

Alex Vazquez avazquez.dev at gmail.com
Sun Jan 17 14:48:36 PST 2016

> Code:
> http://pasted.co/634b16c6
In the code, if I comment the code (background) the effect work fine but
without background. I don't understand why if I paint a black background
and destroy the cairo_t (background) the background affect to the second
cairo_t (effect).
I try with cairo_save/cairo_restore:

    cr = cairo_create (surface);
    cairo_save (cr);
cairo_set_source_rgba (cr, 0, 0, 0, 1);
cairo_set_operator (cr, CAIRO_OPERATOR_SOURCE);
cairo_paint (cr);
cairo_restore (cr);
cairo_destroy (cr);

but don't work.
Is there any way to avoid this ?


2016-01-17 1:25 GMT+01:00 Lawrence D'Oliveiro <ldo at geek-central.gen.nz>:

> On Sat, 16 Jan 2016 23:55:52 +0100, Alex Vazquez wrote:
> > Code:
> > http://pasted.co/634b16c6
> This does not seem to be using alpha transparency anywhere.
> But going back to the original example
> <http://postimg.org/image/ieohdu29t/>, I think I previously
> misunderstood what was going on. Each disc is opaque outside the
> intersecting area. The intersecting part has a mix of the two colours.
> So really, draw each circle with an opaque colour clipped outside the
> other circle. Then fill the mixed colour, clipped to the intersection
> of the two circles.
> --
> cairo mailing list
> cairo at cairographics.org
> http://lists.cairographics.org/mailman/listinfo/cairo
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