[Mesa-dev] [PATCH] i965/blorp: Improve fast color clear comment.

[Kenneth Graunke]

On 12/05/2013 04:47 AM, Paul Berry wrote:
> Clarify the fact that we only optimize full buffer clears using fast
> color clear, and why.
> ---
>  src/mesa/drivers/dri/i965/brw_blorp_clear.cpp | 13 ++++++++++++-
>  1 file changed, 12 insertions(+), 1 deletion(-)
> 
> diff --git a/src/mesa/drivers/dri/i965/brw_blorp_clear.cpp b/src/mesa/drivers/dri/i965/brw_blorp_clear.cpp
> index 1904bde..3af22b6 100644
> --- a/src/mesa/drivers/dri/i965/brw_blorp_clear.cpp
> +++ b/src/mesa/drivers/dri/i965/brw_blorp_clear.cpp
> @@ -238,7 +238,18 @@ brw_blorp_clear_params::brw_blorp_clear_params(struct brw_context *brw,
>        }
>     }
>  
> -   /* If we can do this as a fast color clear, do so. */
> +   /* If we can do this as a fast color clear, do so.
> +    *
> +    * Note that the condition "!partial_clear" means we only try to do full
> +    * buffer clears using fast color clear logic.  This is necessary because
> +    * the fast color clear alignment requirements mean that we typically have
> +    * to clear a larger rectangle than (x0, y0) to (x1, y1).  Restricting fast
> +    * color clears to the full-buffer condition guarantees that the extra
> +    * memory locations that get written to are outside the image boundary (and
> +    * hence irrelevant).  Note that the rectangle alignment requirements are
> +    * never larger than the size of a tile, so there is no danger of
> +    * overflowing beyond the memory belonging to the region.
> +    */
>     if (irb->mt->mcs_state != INTEL_MCS_STATE_NONE && !partial_clear &&
>         wm_prog_key.use_simd16_replicated_data &&
>         is_color_fast_clear_compatible(brw, format, &ctx->Color.ClearColor)) {
> 

Excellent, thanks.

Reviewed-by: Kenneth Graunke <kenneth at whitecape.org>