Boolean Operations on Cairo Paths?

Question

Is there any way to build paths in Cairo by combining two paths together through Boolean operations such as Union, Difference, and Intersection? I'm working on a vector graphics application that uses Cairo to do its rendering and would like to give my users the ability to combine paths together in this manner, but I can't find a way to do it in Cairo.

Lawrenson

Answer 1

I haven't found a way to do this with the cairo libraries. But it's a feature I've been looking for too. Would definitely be helpful when (for example) stroking the combination of two paths - compositing operators mentioned by ntd don't seem to be able to do this.

In the meantime, I'm trying to write scripts for inkscape, and letting inkscape do the unioning/differencing. Acceptable for the problem I'm working on but definitely not for yours. Have you had any luck, either with cairo or any other svg library? After a couple days of googling, it doesn't seem to be trivial :/

Mm

ps - path intersect/combine/overlay is listed on the cairo site as a possible summer-of-code project cairographics.org/summerofcode/ideas – Mm

Answer 2

Combining paths with operators does not make any sense to me. What do you get from "line AND curve OR arc"?

Instead, you can apply compositing operators by using cairo_set_operator(): it will set how the current drawing operation (being it cairo_fill(), cairo_stroke() or whatever) should be mixed with the old content of the surface.

Pandarus

An example of what I mean is the way Inkscape combines paths through boolean operations: usinginkscape.com/node/34. I suppose most of those effects could be achieved through a series of compositing operators, except that places where the two figures' paths intersect wouldn't necessarily have proper line joins. – Lawrenson

I still don't understand the question: inkscape itself uses cairo since version 0.46: wiki.inkscape.org/wiki/index.php/Release_notes/… – Pandarus