This is a UV layout:

http://www.sintel.org/wp-content/uploads/2010/01/face_uv_export.png

it is used in 3D as a 2D representation of a 3D model.
As you can see on the left and right ,the edges would fit together and form a single line.

The issue with texture painting in a 2D paint program is that it is difficult to paint seamlessly so that these seperate edges seem to go on without interuption.


but maybe an other idea is easier to implement:

make it possible to import and "vectorize" uv layouts.
this would result in a "grid mask" (the grid being the actual UV layout) on which you could select the outer edges/points to mark which groups of vertices should connect each other virtually.

so this would mean on the UV layout example:
there are 15 points on the left edge,and 15 points on the right edge of that face layout.
You select the left 15 points,mark as edge/in. Then you select the right 15 points,mark as edge/out.
when drawing over the border of the right edge the stroke should continue in the left edge,wrapping itself in the UV layout.  (for the sake of clarity I will call these "in/out " marks "portals" )


The UV layout should be a guide layer,to be toggled on or off. Only when active should the guide have an effect on the canvas.


It is the same idea as the texture portal curve which I proposed here : https://bugs.kde.org/show_bug.cgi?id=321547
But maybe the gridlike static nature of this idea might make it easier to implement then the curve implementation. 



Note: there are many possible UV layouts. It is certainly possible that there could be multiple UV layout grids. So in effect there could be portals that connect to different grid-layouts. Like connecting a face layout to a neck/body layout.


Note 2: It might be beneficial to think about this from the start: 
a way to STORE,and have ACTIVE several "portals" at once. as not having to remake the same portal selections every time. This way there could be multiple "portals" to toggle between.



if you have more ideas or suggestions or remarks,please discuss