[Mesa-dev] [PATCH] mesa: Match MESA_FORMAT_B5G6R5 for a shallow pixel format of GL_RGB

[Ian Romanick]

On 09/03/2015 09:05 AM, Chris Wilson wrote:
> If the user supplies a pixel format of GL_RGB + GL_UNSIGNED_SHORT_5_6_5
> and specifies a generic unsized GL_RGB internal format, match that to a
> texture format of MESA_FORMAT_B5G6R5 if supported by the hardware.
> 
> Noticed while playing with mesa-demos/teximage:
> 
>   TexImage(RGB/565 256 x 256): 79.8 images/sec, 10.0 MB/sec
>   TexSubImage(RGB/565 256 x 256): 3804.9 images/sec, 475.6 MB/sec
>   GetTexImage(RGB/565 256 x 256): 99.5 images/sec, 12.4 MB/sec
> 
> becomes
> 
>   TexImage(RGB/565 256 x 256): 3439.1 images/sec, 429.9 MB/sec
>   TexSubImage(RGB/565 256 x 256): 3744.1 images/sec, 468.0 MB/sec
>   GetTexImage(RGB/565 256 x 256): 4713.5 images/sec, 589.2 MB/sec
> 
> on a puny Baytrail which is still far from what it is capable of. The
> reason for the disparity is that the teximage demo uses a busy texture
> which is performs an accelerated pixel conversion from the user's B5G6R5
> into the native X8B8G8R8. After the patch, no conversion is required
> allowing use of the blitter and memcpy fast paths.
> 
> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> ---
>  src/mesa/main/texformat.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/src/mesa/main/texformat.c b/src/mesa/main/texformat.c
> index fd9f335..866c7b3 100644
> --- a/src/mesa/main/texformat.c
> +++ b/src/mesa/main/texformat.c
> @@ -114,6 +114,8 @@ _mesa_choose_tex_format(struct gl_context *ctx, GLenum target,
>     case GL_RGB:
>        if (type == GL_UNSIGNED_INT_2_10_10_10_REV) {
>           RETURN_IF_SUPPORTED(MESA_FORMAT_B10G10R10A2_UNORM);
> +      } else if (type == GL_UNSIGNED_SHORT_5_6_5) {
> +         RETURN_IF_SUPPORTED(MESA_FORMAT_B5G6R5_UNORM);

Oh man... I hate this function.  It's such a big pile of hacks.  I think
this change is good for now, but I think you're other idea is in the
right direction.  This function really should check, "If internalFormat
is a generic base format that matches <format,type>, is there supported
format that matches <format,type> exactly?"

Reviewed-by: Ian Romanick <ian.d.romanick at intel.com>

>        }
>        /* fallthrough */
>     case GL_RGB8:
>