[Mesa3d-dev] HELP! with stencil... :)

[<io...@cr...>]

Hi everybody!

I'm doing this question in this list because nobody else could 
answer me in a way I can understand it.  Sorry if this is off-
topic, but my project REALLY needs an answer to this question.
Hope you, Brian, or any other GL expert, can finally tell me
about it.

What happens to a stencil index value in the stencil buffer 
when I specify GL_INCR or GL_DECR as the stencil operations 
to do with glStencilOp() for any of the stencil tests, if I
call glStencilMask() with a mask value different than all 1's?
Does the stencil index gets just incremented/decremented? Or
the value is gathered, incremented/decremented, and then masked
to be written again to the stencil buffer? 

An example:
A fragment at (xw = 50, yw = 50) is about to be renderized at 
the framebuffer. The 16-bit stencil buffer value at (50,50) is
0x003E. The GL is told to GL_INCR the stencil values when the
depth test fails. Additionally, glStencilMask(0xFFEA) was
called. The depth test fails for the fragment at (50,50). What
will be the new value of the stencil buffer at (50,50)
(assuming there are no more operations applied to the stencil
buffer)?

The OpenGL specification is not very clear, at least for me, on 
this subject, so I hope anyone of you can answer me that. 
Thanks in advance.

- Heriberto Delgado
(io...@cr...,
her...@su...)