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

[Brian Paul]

On 12/19/2018 06:47 AM, Ilia Mirkin wrote:
> 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%7C9b8ab75c977c458b597708d665b899b4%7Cb39138ca3cee4b4aa4d6cd83d9dd62f0%7C0%7C0%7C636808240937735266&sdata=pHzFcdG8H%2F89D3rdD2gs7CZ%2BE12BRgGT0uzsuxWDC68%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.

I think Marek did that to squeeze out a few drops of performance.  I 
don't think we have to do that in the feedback code.  But your call.


> 
> 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.

Sure.

-Brian