[Mesa-dev] [PATCH] [swr] fix index buffers with non-zero indices

[Ilia Mirkin]

What's the problem being fixed exactly? We're passing what is
effectively the zero index to the core, and the core shouldn't ever
access data outside of [min, max] + bias.

That said, what you have is probably a cleaner implementation. However
I'm a bit concerned about how it will function with VBO's rather than
client-side arrays. I don't think min_index is guaranteed to be zero
in that case, e.g. it could be set via
glDrawRangeElements[BaseVertex].

So you're effectively mixing a zero-based pointer for VBO and a
min-based pointer for client-side arrays. I don't think this can
work... perhaps you need to add a minVertex in addition to the
maxVertex?

Cheers,

  -ilia

On Tue, Jan 31, 2017 at 11:38 AM, George Kyriazis
<george.kyriazis at intel.com> wrote:
> Fix issue with index buffers that do not contain 0 index.  Use core
> BaseVertex functionality to offset index buffer indices, instead of
> offsetting vertex buffer to point before the buffer origin.
> ---
>  src/gallium/drivers/swr/swr_draw.cpp  | 2 +-
>  src/gallium/drivers/swr/swr_state.cpp | 2 +-
>  2 files changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/src/gallium/drivers/swr/swr_draw.cpp b/src/gallium/drivers/swr/swr_draw.cpp
> index c4d5e5c..88000e5 100644
> --- a/src/gallium/drivers/swr/swr_draw.cpp
> +++ b/src/gallium/drivers/swr/swr_draw.cpp
> @@ -200,7 +200,7 @@ swr_draw_vbo(struct pipe_context *pipe, const struct pipe_draw_info *info)
>                                info->count,
>                                info->instance_count,
>                                info->start,
> -                              info->index_bias,
> +                              info->index_bias - info->min_index,
>                                info->start_instance);
>     else
>        SwrDrawInstanced(ctx->swrContext,
> diff --git a/src/gallium/drivers/swr/swr_state.cpp b/src/gallium/drivers/swr/swr_state.cpp
> index f1f4963..f03f814 100644
> --- a/src/gallium/drivers/swr/swr_state.cpp
> +++ b/src/gallium/drivers/swr/swr_state.cpp
> @@ -1133,7 +1133,7 @@ swr_update_derived(struct pipe_context *pipe,
>              memcpy(scratch, ptr, size);
>              ptr = scratch;
>              scratch += size;
> -            p_data = (const uint8_t *)ptr - base;
> +            p_data = (const uint8_t *)ptr;
>           }
>
>           swrVertexBuffers[i] = {0};
> --
> 2.7.4
>
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