I think that you have to restore after stroke, not before: cr->set_source_rgb(1.0, 1.0, 1.0); cr->fill_preserve(); cr->stroke(); cr->restore(); /// restore after stroke operation, not before <div class="gmail_quote">2012/8/23 Lockert Fredrick <<a href="mailto:lockert.fredrick@gmail.com" target="_blank">lockert.fredrick@gmail.com</a>> <blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"> Greetings, I'm having a bit of a problem with my gtkmm/cairo ellipse shape creation tool. It works as expected, until the mouse pointer is moved in a negative direction of the initial start location (x, y), which results in an invalid matrix exception. After studying the gimp ellipse creation code, I couldn't find anything "obvious", thus I was hoping that someone might be able to point me in the right direction. Full source: <a href="http://fureloka.com/files/dev/gtkmm/drawingprog/" target="_blank">http://fureloka.com/files/dev/gtkmm/drawingprog/</a> ==Ellipse shape creation code== double x = mPt0.x; // Initial mouse click x cord. double y = mPt0.y; // Initial mouse click y cord. double w = mPt1.x; // Real-time mouse pointer x cord. double h = mPt1.y; // Real-time mouse pointer y cord. x = floor(x); y = floor(y); w = ceil(w); h = ceil(h); double center_x = (x + w) / 2.0; double center_y = (y + h) / 2.0; double radius_x = (w - x) / 2.0; double radius_y = (h - y) / 2.0; cr->save(); cr->translate(center_x, center_y); cr->scale(radius_x, radius_y); cr->arc(0.0, 0.0, 1.0, 0.0, 2 * M_PI); cr->set_source_rgb(1.0, 1.0, 1.0); cr->fill_preserve(); cr->restore(); cr->stroke(); As always, any help is highly appreciated! Cheers, Fredrick -- cairo mailing list <a href="mailto:cairo@cairographics.org">cairo@cairographics.org</a> <a href="http://lists.cairographics.org/mailman/listinfo/cairo" target="_blank">http://lists.cairographics.org/mailman/listinfo/cairo</a> </blockquote></div> -- Carlos <a href="http://synfig.org" target="_blank">http://synfig.org</a>