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

[Nanley Chery]

Cc'ing Brian.

I'm planning to make a patch to implement the first (3-step) solution.

On Mon, Aug 17, 2015 at 3:45 PM, Nanley Chery <nanleychery at gmail.com> wrote:

>
> 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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