[Mesa-dev] [PATCH] [v2] i965: Make sure we blit a full compressed block

[Jason Ekstrand]

On Sat, Feb 6, 2016 at 6:11 PM, Ben Widawsky <benjamin.widawsky at intel.com>
wrote:

> This fixes an assertion failure in [at least] one of the Unreal Engine
> Linux
> demo/games that uses DXT1 compression. Specifically, the "Vehicle Game".
>
> At some point, the game ends up trying to blit mip level whose size is 2x2,
> which is smaller than a DXT1 block. As a result, the assertion in the blit
> path
> is triggered. It should be safe to simply make sure we align the width and
> height, which is sadly an example of compression being less efficient.
>
> NOTE: The demo seems to work fine without the assert, and therefore release
> builds of mesa wouldn't stumble over this. Perhaps there is some
> unnoticeable
> corruption, but I had trouble spotting it.
>
> Thanks to Jason for looking at my backtrace and figuring out what was
> going on.
>
> v2: Use NPOT alignment to make sure ASTC is handled properly (Ilia)
> Remove comment about how this doesn't fix other bugs, because it does.
>
> Cc: Jason Ekstrand <jason.ekstrand at intel.com>
> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=93358
> Signed-off-by: Ben Widawsky <benjamin.widawsky at intel.com>
> ---
>  src/mesa/drivers/dri/i965/intel_copy_image.c | 13 +++++++++++++
>  1 file changed, 13 insertions(+)
>
> diff --git a/src/mesa/drivers/dri/i965/intel_copy_image.c
> b/src/mesa/drivers/dri/i965/intel_copy_image.c
> index 0a3337e..42bd7ff 100644
> --- a/src/mesa/drivers/dri/i965/intel_copy_image.c
> +++ b/src/mesa/drivers/dri/i965/intel_copy_image.c
> @@ -212,6 +212,7 @@ intel_copy_image_sub_data(struct gl_context *ctx,
>     struct brw_context *brw = brw_context(ctx);
>     struct intel_mipmap_tree *src_mt, *dst_mt;
>     unsigned src_level, dst_level;
> +   GLuint bw, bh;
>
>     if (_mesa_meta_CopyImageSubData_uncompressed(ctx,
>                                                  src_image,
> src_renderbuffer,
> @@ -275,6 +276,18 @@ intel_copy_image_sub_data(struct gl_context *ctx,
>     intel_miptree_all_slices_resolve_depth(brw, dst_mt);
>     intel_miptree_resolve_color(brw, dst_mt);
>
> +   _mesa_get_format_block_size(src_mt->format, &bw, &bh);
> +   /* It's legal to have a WxH that's smaller than a compressed block.
> This
> +    * happens for example when you are using a higher level LOD. For this
> case,
> +    * we still want to copy the entire block, or else the decompression
> will be
> +    * incorrect.
> +    */
> +   if (src_width < bw)
> +      src_width = ALIGN_NPOT(src_width, bw);
> +
> +   if (src_height < bh)
> +      src_height = ALIGN_NPOT(src_height, bh);
>

I've been going back-and-forth as to whether or not this is the right place
to do this or if we wanted it further up or down the stack.  At the end of
the day, I concluded that it's as good a place as any.

Reviewed-by: Jason Ekstrand <jason.ekstrand at intel.com>
Cc "11.0 11.1" <mesa-stable at lists.freedesktop.org>

--Jason


> +
>     if (copy_image_with_blitter(brw, src_mt, src_level,
>                                 src_x, src_y, src_z,
>                                 dst_mt, dst_level,
> --
> 2.7.0
>
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