[Mesa-dev] [PATCH 1/4] mesa/formats: only do type and component lookup for uncompressed formats

[Nanley Chery]

On Fri, Aug 14, 2015 at 4:00 PM, Chad Versace <chad.versace at intel.com>
wrote:

> On Tue 11 Aug 2015, Nanley Chery wrote:
> > From: Nanley Chery <nanley.g.chery at intel.com>
> >
> > Only uncompressed formats have a non-void type and actual components per
> pixel.
> > Rename _mesa_format_to_type_and_comps to
> > _mesa_uncompressed_format_to_type_and_comps and require callers to check
> if
> > the format is not compressed.
> >
> > Cc: Jason Ekstrand <jason.ekstrand at intel.com>
> > Signed-off-by: Nanley Chery <nanley.g.chery at intel.com>
> > ---
> >  src/mesa/main/format_utils.c |  2 +-
> >  src/mesa/main/formats.c      | 55
> ++++++++------------------------------------
> >  src/mesa/main/formats.h      |  2 +-
> >  src/mesa/main/mipmap.c       |  2 +-
> >  4 files changed, 12 insertions(+), 49 deletions(-)
>
> I like several patches in this series, but I don't like this one. It
> produces a lot of compiler warnings.
>
> The problem is that the switch in _mesa_format_to_type_and_comps() is
> intended to be an exhaustive switch. Removing the compressed format
> cases causes a waterfall of compiler warnings like this:
>
>   main/formats.c:1458:4: warning: enumeration value
> 'MESA_FORMAT_LA_LATC2_UNORM' not handled in switch [-Wswitch]
>   main/formats.c:1458:4: warning: enumeration value
> 'MESA_FORMAT_LA_LATC2_SNORM' not handled in switch [-Wswitch]
>   main/formats.c:1458:4: warning: enumeration value
> 'MESA_FORMAT_ETC1_RGB8' not handled in switch [-Wswitch]
>   main/formats.c:1458:4: warning: enumeration value
> 'MESA_FORMAT_ETC2_RGB8' not handled in switch [-Wswitch]
>   main/formats.c:1458:4: warning: enumeration value
> 'MESA_FORMAT_ETC2_SRGB8' not handled in switch [-Wswitch]
>   main/formats.c:1458:4: warning: enumeration value
> 'MESA_FORMAT_ETC2_RGBA8_EAC' not handled in switch [-Wswitch]
>   main/formats.c:1458:4: warning: enumeration value
> 'MESA_FORMAT_ETC2_SRGB8_ALPHA8_EAC' not handled in switch [-Wswitch]
>
> I think you can salvage the patch by following the hint in this deleted
> hunk...
>
> > -   case MESA_FORMAT_RGB_FXT1:
> > -   case MESA_FORMAT_RGBA_FXT1:
> > -   case MESA_FORMAT_RGB_DXT1:
> > -   case MESA_FORMAT_RGBA_DXT1:
> > -   case MESA_FORMAT_RGBA_DXT3:
> > -   case MESA_FORMAT_RGBA_DXT5:
> > -   case MESA_FORMAT_SRGB_DXT1:
> > -   case MESA_FORMAT_SRGBA_DXT1:
> > -   case MESA_FORMAT_SRGBA_DXT3:
> > -   case MESA_FORMAT_SRGBA_DXT5:
> > -   case MESA_FORMAT_R_RGTC1_UNORM:
> > -   case MESA_FORMAT_R_RGTC1_SNORM:
> > -   case MESA_FORMAT_RG_RGTC2_UNORM:
> > -   case MESA_FORMAT_RG_RGTC2_SNORM:
> > -   case MESA_FORMAT_L_LATC1_UNORM:
> > -   case MESA_FORMAT_L_LATC1_SNORM:
> > -   case MESA_FORMAT_LA_LATC2_UNORM:
> > -   case MESA_FORMAT_LA_LATC2_SNORM:
> > -   case MESA_FORMAT_ETC1_RGB8:
> > -   case MESA_FORMAT_ETC2_RGB8:
> > -   case MESA_FORMAT_ETC2_SRGB8:
> > -   case MESA_FORMAT_ETC2_RGBA8_EAC:
> > -   case MESA_FORMAT_ETC2_SRGB8_ALPHA8_EAC:
> > -   case MESA_FORMAT_ETC2_R11_EAC:
> > -   case MESA_FORMAT_ETC2_RG11_EAC:
> > -   case MESA_FORMAT_ETC2_SIGNED_R11_EAC:
> > -   case MESA_FORMAT_ETC2_SIGNED_RG11_EAC:
> > -   case MESA_FORMAT_ETC2_RGB8_PUNCHTHROUGH_ALPHA1:
> > -   case MESA_FORMAT_ETC2_SRGB8_PUNCHTHROUGH_ALPHA1:
> > -   case MESA_FORMAT_BPTC_RGBA_UNORM:
> > -   case MESA_FORMAT_BPTC_SRGB_ALPHA_UNORM:
> > -   case MESA_FORMAT_BPTC_RGB_SIGNED_FLOAT:
> > -   case MESA_FORMAT_BPTC_RGB_UNSIGNED_FLOAT:
> > -      /* XXX generate error instead? */
> > -      *datatype = GL_UNSIGNED_BYTE;
> > -      *comps = 0;
> > -      return;
> > -
>
> In other words, rename the function to
> _mesa_uncompressed_format_to_type_and_comps(); keep all the format
> cases; and add an assertion or _mesa_problem() for the compressed cases.
>

I was hoping to avoid having to add cases to the switch for compressed
textures because they are all invalid inputs. Nonetheless, your proposed
solution is a good one.

I do have some alternative ideas that I'd like to share. After a little
more investigation, it seems that we have redundant checking that new
formats have their datatype and components assigned. The first check is at
compile time; the compiler checks that every enum has a case. The second
check is at run-time for debug builds; in check_format_to_type_and_comps(),
we pass every format through _mesa_uncompressed_format_to_type_and_comps()
during context init (but don't do anything when an error is emitted). Both
checks serve to remind the developer to add a case to the switch whenever a
new format is added to the mesa_format enum.

We could remove this redundancy and only update the cases for the formats
that matter (uncompressed formats) by doing the following:
1. in _mesa_uncompressed_format_to_type_and_comps: unconditionally add the
default case with an assertion that what has fallen through was either a
compressed format or MESA_FORMAT_NONE.
2. in check_format_to_type_and_comps(): assert that the datatype value is
greater than 0 to ensure the test fails in an error state.
3. in src/mesa/main/tests/ : make _mesa_test_formats() a test we run during
make check.

We could also remove the redundant checking (but keep adding unnecessary
compressed cases by doing the following:
1. keep the compressed cases as suggested
2. delete check_format_to_type_and_comps() (since the compiler does this
for us).

Nanley
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