[Mesa-dev] [PATCH] st/mesa: allow glDrawElements to work with GL_SELECT feedback

[Ilia Mirkin]

On Wed, Dec 19, 2018 at 8:38 AM Brian Paul <brianp at vmware.com> wrote:
>
> On 12/18/2018 08:50 PM, Ilia Mirkin wrote:
> > Not sure if this ever worked, but the current logic for setting the
> > min/max index is definitely wrong for indexed draws. While we're at it,
> > bring in all the usual logic from the non-indirect drawing path.
> >
> > Bugzilla: https://na01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fbugs.freedesktop.org%2Fshow_bug.cgi%3Fid%3D109086&data=02%7C01%7Cbrianp%40vmware.com%7C6caf58471242445a386a08d665652d9a%7Cb39138ca3cee4b4aa4d6cd83d9dd62f0%7C0%7C0%7C636807882586735220&sdata=ekxW8vXjInP6H7vsVCdLJ4GD9y%2BN8MYpzWYRY87utEA%3D&reserved=0
> > Signed-off-by: Ilia Mirkin <imirkin at alum.mit.edu>
> > ---
> >
> > This makes it more or less mirror st_draw_vbo. As the comment in the
> > code says, would be nice to refactor, but ... meh.
> >
> > Note that I haven't tested any of the interactions with additional
> > features, like primitive restart or instancing or any of that. However I
> > don't think that this would make things *worse*.
> >
> >   src/mesa/state_tracker/st_draw_feedback.c | 61 +++++++++++++++--------
> >   1 file changed, 39 insertions(+), 22 deletions(-)
> >
> > diff --git a/src/mesa/state_tracker/st_draw_feedback.c b/src/mesa/state_tracker/st_draw_feedback.c
> > index 6ec6d5c16f4..49fdecf7e38 100644
> > --- a/src/mesa/state_tracker/st_draw_feedback.c
> > +++ b/src/mesa/state_tracker/st_draw_feedback.c
> > @@ -84,27 +84,6 @@ set_feedback_vertex_format(struct gl_context *ctx)
> >   }
> >
> >
> > -/**
> > - * Helper for drawing current vertex arrays.
> > - */
> > -static void
> > -draw_arrays(struct draw_context *draw, unsigned mode,
> > -            unsigned start, unsigned count)
> > -{
> > -   struct pipe_draw_info info;
> > -
> > -   util_draw_init_info(&info);
> > -
> > -   info.mode = mode;
> > -   info.start = start;
> > -   info.count = count;
> > -   info.min_index = start;
> > -   info.max_index = start + count - 1;
> > -
> > -   draw_vbo(draw, &info);
> > -}
> > -
> > -
> >   /**
> >    * Called by VBO to draw arrays when in selection or feedback mode and
> >    * to implement glRasterPos.
> > @@ -136,10 +115,18 @@ st_feedback_draw_vbo(struct gl_context *ctx,
> >      struct pipe_transfer *ib_transfer = NULL;
> >      GLuint i;
> >      const void *mapped_indices = NULL;
> > +   struct pipe_draw_info info;
> >
> >      if (!draw)
> >         return;
> >
> > +   /* Initialize pipe_draw_info. */
> > +   info.primitive_restart = false;
> > +   info.vertices_per_patch = ctx->TessCtrlProgram.patch_vertices;
> > +   info.indirect = NULL;
> > +   info.count_from_stream_output = NULL;
> > +   info.restart_index = 0;
>
> Shouldn't we use util_draw_init_info() to make this future-proof?
>
> Looks good otherwise.  Thanks for fixing this!
>
> Reviewed-by: Brian Paul <brianp at vmware.com>

I'm just copying what st_draw_vbo does. I think keeping them looking
similar is important so that any updates to one are easily ported. Why
doesn't that use the util_draw_init_info? Not sure.

At this point, the only differences are in ib setup -- this function
will forcefully map the ib (which I think is fine) -- and lack of
support for count_from_stream_output. The latter would take a bit of
work, since we can't just pass it in directly -- it's a pipe_query
from a (potentially) different driver. When someone complains about
glDrawTransformFeedback not working with GL_SELECT, we can reconsider.

  -ilia