[cairo] Non-transparent composition of transparent objects

[Uli Schlachter]

Hi,

On 13.11.2013 09:09, LRN wrote:
> The [1] shows the output various composition operators, but the effect
> i'd like to achieve is not obvious from that documentation.
> 
> What i want to do is to draw two transparent objects in sequence, and
> second object should be painted only in places where first object
> isn't (at all).
> 
> Now, AFAICS, this can be achieved by just using CAIRO_OPERATOR_SOURCE
> and drawing object in reverse order: second object is drawn, then
> first object is drawn on top of it, resulting in a composition of
> both, where second object can be seen only in places where first isn't.
> 
> Doesn't seem to be working though, because i'm drawing with surface
> patterns.
[...]

Doesn't the operator source just remove your second object again?

I think that what you are looking for is cairo_mask_surface() instead. But I am
not really sure how to do the "not at all" part of your requirements.

Uli
-- 
"Why make things difficult, when it is possible to make them cryptic
and totally illogical, with just a little bit more effort?" -- A. P. J.