[Mesa-dev] Gallium: Removal of set_index_buffer (discussion)
maraeo at gmail.com
Mon Feb 20 19:56:59 UTC 2017
On Mon, Feb 20, 2017 at 8:29 PM, Axel Davy <axel.davy at ens.fr> wrote:
> On 20/02/2017 20:11, Ilia Mirkin wrote:
>> On Mon, Feb 20, 2017 at 2:01 PM, Marek Olšák <maraeo at gmail.com> wrote:
>>> I'd like to remove pipe_context::set_index_buffer. It's not useful to
>>> most drivers and the interface is inconvenient for Mesa/OpenGL,
>>> because it's a draw state that is set with a separate driver callback,
>>> which is an unnecessary driver roundtrip taking some CPU cycles. I'd
>>> prefer to pass the index buffer via pipe_draw_info.
>>> I'm aware that the interface was inherited from DX10, but I don't
>>> think that makes any difference here. DX10 state trackers can pass the
>>> index buffer via pipe_draw_info too.
>>> This is my proposal:
>>> iff --git a/src/gallium/include/pipe/p_state.h
>>> index ce19b92..cffbb33 100644
>>> --- a/src/gallium/include/pipe/p_state.h
>>> +++ b/src/gallium/include/pipe/p_state.h
>>> @@ -635,7 +635,7 @@ struct pipe_index_buffer
>>> struct pipe_draw_info
>>> - boolean indexed; /**< use index buffer */
>>> + ubyte index_size; /**< 0 = non-indexed */
> Isn't that enough to say non-index when index_buffer and user_indices are
> NULL ?
We still need index_size and it's only 8 bits as opposed to 64 bits.
>>> enum pipe_prim_type mode; /**< the mode of the primitive */
>>> boolean primitive_restart;
>>> ubyte vertices_per_patch; /**< the number of vertices per patch */
>>> @@ -666,12 +666,18 @@ struct pipe_draw_info
>>> unsigned indirect_params_offset; /**< must be 4 byte aligned */
>>> + /**
>>> + * Index buffer. Only one can be non-NULL.
>>> + */
>>> + struct pipe_resource *index_buffer; /* "start" is the offset */
>> Works for me. Is start the offset in bytes or is start * index_size
>> the offset in bytes?
> Same question here. My understanding is that start is in terms of start *
> index_size bytes.
offset = start * index_size;
> But we really want to have a byte offset.
The offset should be aligned to index_size, otherwise hardware won't work.
>>> + void *user_indices;
>>> /* Pointers must be at the end for an optimal structure layout on
>>> 64-bit. */
>>> Comments welcome,
>>> mesa-dev mailing list
>>> mesa-dev at lists.freedesktop.org
>> mesa-dev mailing list
>> mesa-dev at lists.freedesktop.org
> My understanding of the current interface is that setting the index buffer
> may be costly. Thus you want to set once, and use for several draw calls
> with different start or other changes.
Not true. It's there only because the interface is based on DX10.
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