Created attachment 141687 [details]
probably the buggy shader

Ok, so we figured out the shader I mentionned in my last message was supposed
to render on top of a "white" engine which didn't appear on radeonsi.

So here is now the shader that draws (earlier) the "white" engine.

This one has alpha test enabled and stencil test enabled. There are two version
of the shader in the log that get compiled (I guess two alpha test set of
parameters), I don't know which is used, thus I put both.

It features on kill_if inside an if. Perhaps something to look at.