[Mesa-dev] [PATCH 1/4] mesa/teximage: use correct extension for accept stencil texture.

[Pohjolainen, Topi]

On Sun, Apr 05, 2015 at 08:22:13PM +0300, Pohjolainen, Topi wrote:
> On Sun, Apr 05, 2015 at 08:06:50PM +0300, Pohjolainen, Topi wrote:
> > On Sun, Apr 05, 2015 at 08:46:16AM -0400, Ilia Mirkin wrote:
> > > While this change is correct, the Intel guys will yell at you, because
> > > they're somehow misusing this in meta for Broadwell, s.t. this will
> > > cause crashes when blitting stencil. IMHO that's a problem that should
> > > be fixed in their driver and this can go on, but... it's also not my
> > > driver that's crashing -- they might feel differently :)
> > 
> > As far as I can tell we only do:
> > 
> >    _mesa_TexParameteri(target, GL_DEPTH_STENCIL_TEXTURE_MODE,
> >                        GL_STENCIL_INDEX);
> > 
> > which suppose to be the right thing to do - we select the stencil to be
> > sampled instead of depth. And this won't hit the path below. I made the
> > change locally and I'm now running piglit on broadwell.
> > 
> > I noticed that _mesa_base_tex_format() is in turn used in
> > 
> > src/mesa/drivers/common/meta_blit.c
> > 
> > but we shouldn't go there with intel driver ever. On hardware older than
> > broadwell we don't use meta and the one used on broadwell and newer
> > is found in:
> > 
> > src/mesa/drivers/dri/i965/brw_meta_stencil_blit.c
> > 
> > But lets see what piglit says.
> 
> Right you are. This is more subtle, we will hit it when we actually create
> a temporary texture out of the given read renderbuffer. It seems that this
> was hit first time when formats where adjusted and then Jason added the
> conditional using ARB_stencil_texturing (which is not right either).
> 
> Really sorry that this is hindering your work now. I'll try to take a look
> at this tomorrow.

So far I can't come up with other things than pure hacks. I'll explain
a little what happens in the "intel stencil meta blit". Like I said, the
driver creates a temporary texture out of the stencil attachment:

   const struct gl_renderbuffer_attachment *att =
      &ctx->ReadBuffer->Attachment[BUFFER_STENCIL];
   struct gl_renderbuffer *rb = att->Renderbuffer;
   struct gl_texture_object *tex_obj;

   ...
      if (!_mesa_meta_bind_rb_as_tex_image(ctx, rb, &blit->tempTex, &tex_obj,
                                          target)) {


This gets wound back to the driver, a call to
intel_bind_renderbuffer_tex_image() which in turn calls the core again.

   _mesa_init_teximage_fields(ctx, image,
                              rb->Width, rb->Height, 1,
                              0, rb->InternalFormat, rb->Format);

Here "rb->InternalFormat" is GL_STENCIL_INDEX that won't be accepted by
_mesa_base_tex_format() anymore without ARB_texture_stencil8. As most of
the texture image setting up logic takes place in the core, the boolean state
flag (brw_context::meta_in_progress) we have in intel driver is not much
help. It looks that we would need additional driver driven overriding.
But I don't like that at all.

I'll look into this some more, but any suggestions are welcome.