workaround for multiple scene manager and pass hash pb

[madmarx]

Hello everyone,

I got the assert :retPair.second && "Error inserting new pass entry into PassGroupRenderableMap".
So it is the same problem as a few pointed out :
https://www.ogre3d.org/forums/viewtopic.php?f=1&t=40839
(there are other topics)

I have 2 scene managers, and I can't change some elements of a textureunit without getting the assert.

Unfortunatelly, the method described in the quoted topic did not succed to resolve the problem for me (even if I "iterates through every scene manager, gets its render queue and clears it using clear(true) and then call processPendingPassUpdates." i get the assert).

So I would appreciate even an 'unclean' method that at-least work ... Or documentation about what happens, in order to try a solution.
What I currently understand is only :
1/ there is a renderqueue per scenemanager.
2/ there is an iteration though the renderqueue, and things get drawn.
So there is a big gap in my knowledge... any explanation would be welcome. If I understand what is the problem, I can work to propose a solution.

Pierre