[Mesa-dev] [PATCH v2 1/8] mesa: Track changes to transform feedback state.

[Paul Berry]

On 14 December 2011 13:54, Marek Olšák <maraeo at gmail.com> wrote:

> On Wed, Dec 7, 2011 at 8:09 PM, Paul Berry <stereotype441 at gmail.com>
> wrote:
> > This patch adds a new bit to the ctx->NewState bitfield,
> > _NEW_TRANSFORM_FEEDBACK, to track state changes that affect
> > ctx->TransformFeedback.  This bit can be used by driver back-ends to
> > avoid expensive recomputations when transform feedback state has not
> > been modified.
> >
> > Reviewed-by: Kenneth Graunke <kenneth at whitecape.org>
> > ---
> >  src/mesa/main/mtypes.h            |    1 +
> >  src/mesa/main/transformfeedback.c |    9 ++++++++-
> >  2 files changed, 9 insertions(+), 1 deletions(-)
> >
> > diff --git a/src/mesa/main/mtypes.h b/src/mesa/main/mtypes.h
> > index 33b00c6..fc494f7 100644
> > --- a/src/mesa/main/mtypes.h
> > +++ b/src/mesa/main/mtypes.h
> > @@ -3051,6 +3051,7 @@ struct gl_matrix_stack
> >  #define _NEW_PROGRAM_CONSTANTS (1 << 27)
> >  #define _NEW_BUFFER_OBJECT     (1 << 28)
> >  #define _NEW_FRAG_CLAMP        (1 << 29)
> > +#define _NEW_TRANSFORM_FEEDBACK (1 << 30) /**<
> gl_context::TransformFeedback */
> >  #define _NEW_ALL ~0
> >  /*@}*/
> >
> > diff --git a/src/mesa/main/transformfeedback.c
> b/src/mesa/main/transformfeedback.c
> > index 11abd03..799245d 100644
> > --- a/src/mesa/main/transformfeedback.c
> > +++ b/src/mesa/main/transformfeedback.c
> > @@ -376,6 +376,7 @@ _mesa_BeginTransformFeedback(GLenum mode)
> >       return;
> >    }
> >
> > +   FLUSH_VERTICES(ctx, _NEW_TRANSFORM_FEEDBACK);
> >    obj->Active = GL_TRUE;
> >    ctx->TransformFeedback.Mode = mode;
> >
> > @@ -398,6 +399,7 @@ _mesa_EndTransformFeedback(void)
> >       return;
> >    }
> >
> > +   FLUSH_VERTICES(ctx, _NEW_TRANSFORM_FEEDBACK);
> >    ctx->TransformFeedback.CurrentObject->Active = GL_FALSE;
> >
> >    assert(ctx->Driver.EndTransformFeedback);
> > @@ -415,6 +417,7 @@ bind_buffer_range(struct gl_context *ctx, GLuint
> index,
> >  {
> >    struct gl_transform_feedback_object *obj =
> >       ctx->TransformFeedback.CurrentObject;
> > +   FLUSH_VERTICES(ctx, _NEW_TRANSFORM_FEEDBACK);
> >
> >    /* The general binding point */
> >    _mesa_reference_buffer_object(ctx,
>
> Sorry for the late reply.
>
> There's no need to set _NEW_TRANSFORM_FEEDBACK in bind_buffer_range,
> because it's not allowed to change buffer bindings for an active TFB
> object. Buffer bindings can only be changed for inactive TFB objects.
> And because they're inactive, the drivers don't need to know about it.
> The TFB buffers are effectively bound through BeginTransformFeedback
> and unbound through EndTransformFeedback (likewise for Resume and
> Pause).
>
> Marek
>

Ah, you're right.  I missed this subtlety.  I've already landed this patch,
so I'll submit a follow-up patch that replaces the unnecessary calls to
FLUSH_VERTICES() with comments explaining why a flush is unnecessary.
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