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

[Erik Faye-Lund]

On Wed, Sep 9, 2015 at 11:25 AM, Chris Wilson <chris at chris-wilson.co.uk> wrote:
> On Wed, Sep 09, 2015 at 11:11:59AM +0200, Erik Faye-Lund wrote:
>> On Thu, Sep 3, 2015 at 6:05 PM, Chris Wilson <chris at chris-wilson.co.uk> 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);
>>
>> Shouldn't this be MESA_FORMAT_R5G6B5_UNORM? AFAICT, the reason for
>> using BGR above, is the _REV suffix on the type...
>
> No, it's the first line that's "wrong" since the B10G10R10A2 matches
> GL_BGRA + GL_UNSIGNED_INT_2_10_10_10_REV, GL_RGB implies that the
> incoming data only has 3 channels (no alpha at all).

Good point about the alpha channel. It sounds like it should be
changed to MESA_FORMAT_B10G10R10X2_UNORM instead.

But according to src/mesa/main/format_pack.c's
pack_ubyte_b10g10r10a2_unorm(), mesa's B10G10R10A2 corresponds to
OpenGL's UNSIGNED_INT_2_10_10_10_REV. So I think it matches GL_RGBA,
not GL_BGRA. The latter would mean another swizzle, AFAICT.

> i965 know how to do B5G6R5 and not R5G6B5, but for completeness we could
> also add RETURN_IF_SUPPORTED(MESA_FORMAT_R5G6B5_UNORM);

I think intel-specific hacks (like preferring B5G6R5 over R5G6B5)
shouldn't leak into _mesa_choose_tex_format(), so I think it'd be a
good move to add "RETURN_IF_SUPPORTED(MESA_FORMAT_R5G6B5_UNORM);"
before the latter return.