Hi Diaco,
one question regarding your Codepen example, as it seems to face the same issue as we are experiencing for our usecase.
At the 'touch-area' of two shapes (or in your example the area where the two masked svg-shapes touch), browsers do render a thin line when the shapes are positioned in certain orientations in 3d-space.
I modified you Codepen example so that the ring is being filled with white color: http://codepen.io/anon/pen/xOGRjJ
Now you should be able to see a thin line being rendered where the two shapes touch. We could observe this behavior for Chrome and FF on Windows as well for Chrome and FF on Mac. I attached a screenshot where the rendering-error is visible, too:
Any ideas how to fix this issue?
Best,
Clemens
