I’ve found this reply, and it works flawlessly in “multitexture” mode (Blender Internal):
But I’ve tried to use it with GLSL viewport shading and in that case the faces don’t get hidden.
Now, the workaround is to separate part of the model (make separate objects) and hide these, but this is not practical, especially with models that are in one piece and with lots of cavities… am I missing something?
Is there a way in GLSL too?
not very practical (as it needs to keep adding and removing vertices to a vertexgroup), but you can use the mask modifier.
In solid view mode
Select faces to hide
Press H to hide them
Go to texture paint with the face select masking on
Press A to select all faces
Paint
Alt+H to unhide
Secrop: Yes, that is a very good workaround! Thanks for sharing 
By the way, I see in the modifier that you can select the group, so maybe rather than adding and removing it is possible to “prepare” the desired groups and switch the whole group instead of adding and removing verts. Example… one group for the coat/hood, one for the hat/glasses/hair… anything that "gets in the way while painting. The only drawback in this is that if you already have tons of small groups for rigging, it can get quite confusing! But if you don’t is is probably even better than what I was looking for,
Richard Marklew:
Yep, that works, thanks!
(I wonder why it doesn’t just work “out of the box”… like in multitexture)
(I wonder why it doesn’t just work “out of the box”… like in multitexture)
?? The only non ‘out of the box’ changes from the factory settings are changing to GLSL shading and enabling face masking
In “multitexture” shading mode you just activate ‘mask’ and press H, directly from paint mode. No need to go in edit, activate solid, go back to paint and activate mask. This is what I mean. Maybe “out of the box” is not the right term. I wasn’t referring to the factory settings. Out of the box in the sense of “directly from paint” like it does in multitexture shading.
