[Mesa-dev] [PATCH] i965: allocate at least 1 BLEND_STATE element

[Kenneth Graunke]

On Monday, July 06, 2015 04:24:12 PM Emil Velikov wrote:
> Hello gents,
> 
> On 2 July 2015 at 08:45, Kenneth Graunke <kenneth at whitecape.org> wrote:
> > On Wednesday, July 01, 2015 10:16:28 AM Mike Stroyan wrote:
> >> When there are no color buffer render targets, gen6 and gen7 still
> >> use the first BLEND_STATE element to determine alpha test.
> >> gen6_upload_blend_state was allocating zero elements when
> >> ctx->Color.AlphaEnabled was false.
> >> That left _3DSTATE_CC_STATE_POINTERS or _3DSTATE_BLEND_STATE_POINTERS
> >> pointing to random data from some previous brw_state_batch().
> >> That sometimes suppressed depth rendering when those bits
> >> happened to mean COMPAREFUNC_NEVER.
> >> This produced flickering shadows for dota2 reborn.
> >> ---
> >>  src/mesa/drivers/dri/i965/gen6_cc.c | 2 +-
> >>  1 file changed, 1 insertion(+), 1 deletion(-)
> >>
> >> diff --git a/src/mesa/drivers/dri/i965/gen6_cc.c b/src/mesa/drivers/dri/i965/gen6_cc.c
> >> index 2bfa271..2b76e24 100644
> >> --- a/src/mesa/drivers/dri/i965/gen6_cc.c
> >> +++ b/src/mesa/drivers/dri/i965/gen6_cc.c
> >> @@ -51,7 +51,7 @@ gen6_upload_blend_state(struct brw_context *brw)
> >>      * with render target 0, which will reference BLEND_STATE[0] for
> >>      * alpha test enable.
> >>      */
> >> -   if (nr_draw_buffers == 0 && ctx->Color.AlphaEnabled)
> >> +   if (nr_draw_buffers == 0)
> >>        nr_draw_buffers = 1;
> >>
> >>     size = sizeof(*blend) * nr_draw_buffers;
> >>
> >
> > Great catch!
> >
> > Reviewed-by: Kenneth Graunke <kenneth at whitecape.org>
> >
> > And pushed:
> >    9d408a4..fe2b748  master -> master
> >
> > I think we ought to change gen8_blend_state.c as well, but I'm not quite
> > sure what change to make.  Either we should make the same change you did
> > here, or delete the whole "We need at least 1 BLEND_STATE written"
> > block.
> >
> > On Gen8+, it looks like the alpha test and other functions that might
> > discard pixels are all in the shared/common DWord, and the per-color
> > target DWord pairs look relatively harmless.  I suppose the null RT
> > would still refer to BLEND_STATE[0]...so it might still be worth
> > emitting one.  Any thoughts?
> Should we get this into 10.6 or there are some not so obvious
> dependencies that we're missing in the 10.6 branch ? Asking every user
> to rebuild mesa just to play Dota2 seems unreasonable imho.
> 
> Cheers,
> Emil

Yeah, it should definitely land in 10.6.    I think I just forgot to add
the Cc stable tag (sorry!).  It shouldn't have any dependencies.

--Ken
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