[Mesa3d-dev] Minor Mesa demo bug.

[Bill W. <bil...@gr...>]

The function ShowDepthBuffer disables depth and stencil testing.  However,
it doesn't include GL_ENABLE_BIT in its bitmask for glPushAttrib.  This
means that the depth and stencil testing is inadvertently disabled by
ShowDepthBuffer.  You can't see it in reflect, since the depth test is
enabled there explicitly.  If you put a ShowDepthBuffer into gears, look
at the depth buffer, and then look at the color buffer, it displays
incorrectly.

I'm assuming that the stencil enabled state is not part of the state saved
by GL_DEPTH_BUFFER_BIT in glPushAttrib.  The spec is not clear about
this, at least to my reading.  The Stencil enabled state is saved and
restored by glPushAttrib/glPopAttrib, with the GL_STENCIL_BUFFER_BIT.
Several other state enabled/disabled bits are enabled both by GL_ENABLE_BIT
and GL_MUMBLE_BIT.

In any case, the fix is trivial.  Either include GL_ENABLE_BIT in 
ShowDepthBuffer,
or else restore the depth enabled state in _mesa_PopAttrib.  The depth enabled
state is stored with _mesa_PushAttrib, so restoring it is possible.