[Mesa-dev] [PATCH] i965: Momentarily pretend to support ARB_texture_stencil8 for blits.

[Martin Peres]

On 10/06/2015 01:18, Kenneth Graunke wrote:
> Broadwell's stencil blitting code attempts to bind a renderbuffer as a
> texture, using dd->BindRenderbufferTexImage().
>
> This calls _mesa_init_teximage_fields(), which then attempts to set
> img->_BaseFormat = _mesa_base_tex_format(ctx, internalFormat), which
> assert fails if internalFormat is GL_STENCIL_INDEX8 but
> ARB_texture_stencil8 is unsupported.
>
> To work around this, just pretend to support the extension momentarily,
> during the blit.  Meta has already munged a variety of other things in
> the context (including the API!), so it's not that much worse than what
> we're already doing.
>
> Fixes regressions since commit f7aad9da20b13c98f77d6a690b327716f39c0a47
> (mesa/teximage: use correct extension for accept stencil texture.).
>
> Signed-off-by: Kenneth Graunke <kenneth at whitecape.org>
> Cc: airlied at gmail.com
> Cc: imirkin at alum.mit.edu
> ---
>   src/mesa/drivers/dri/i965/brw_meta_stencil_blit.c | 2 ++
>   1 file changed, 2 insertions(+)
>
> Here's a brown paper bag fix.  I had apparently run all of Piglit with Dave's
> patch in place, but I'd accidentally built Mesa with "--enable-debuga", so
> no assertions.
>
> I think this is the best thing to do for now.  Alternatives would be:
> 1. Delete the assertion in _mesa_init_teximage_fields() [very lame]
> 2. Make intel_bind_renderbuffer_tex_image lie about the formats and
>     then fix them up.  [seems like more work]
> 3. Just enable the extension
>     [I don't want to do this without consulting Topi, and he's on vacation]
>     [would also need a lot of testing...]
>
> *shrug*.  This works.  It's easy.
>
> diff --git a/src/mesa/drivers/dri/i965/brw_meta_stencil_blit.c b/src/mesa/drivers/dri/i965/brw_meta_stencil_blit.c
> index fc7018d..4a33de9 100644
> --- a/src/mesa/drivers/dri/i965/brw_meta_stencil_blit.c
> +++ b/src/mesa/drivers/dri/i965/brw_meta_stencil_blit.c
> @@ -414,6 +414,7 @@ brw_meta_stencil_blit(struct brw_context *brw,
>      GLenum target;
>   
>      _mesa_meta_fb_tex_blit_begin(ctx, &blit);
> +   ctx->Extensions.ARB_texture_stencil8 = true;
>   
>      _mesa_GenFramebuffers(1, &fbo);
>      /* Force the surface to be configured for level zero. */
> @@ -451,6 +452,7 @@ brw_meta_stencil_blit(struct brw_context *brw,
>      _mesa_DrawArrays(GL_TRIANGLE_FAN, 0, 4);
>   
>   error:
> +   ctx->Extensions.ARB_texture_stencil8 = false;
>      _mesa_meta_fb_tex_blit_end(ctx, target, &blit);
>      _mesa_meta_end(ctx);
>   
Please add FIXMEs around your additions to explain the hack!