[Mesa-dev] [PATCH] st/mesa: handle SNORM formats in generic CopyPixels path

[Dave Airlie]

On Mon, Jun 24, 2013 at 6:12 PM, Jose Fonseca <jfonseca at vmware.com> wrote:
>
>
> ----- Original Message -----
>> ---
>>  src/gallium/auxiliary/util/u_format.c     | 14 ++++++++++++++
>>  src/gallium/auxiliary/util/u_format.h     |  3 +++
>>  src/mesa/state_tracker/st_cb_drawpixels.c |  6 ++++++
>>  3 files changed, 23 insertions(+)
>>
>> diff --git a/src/gallium/auxiliary/util/u_format.c
>> b/src/gallium/auxiliary/util/u_format.c
>> index 9bdc2ea..b70c108 100644
>> --- a/src/gallium/auxiliary/util/u_format.c
>> +++ b/src/gallium/auxiliary/util/u_format.c
>> @@ -131,6 +131,20 @@ util_format_is_pure_uint(enum pipe_format format)
>>     return (desc->channel[i].type == UTIL_FORMAT_TYPE_UNSIGNED &&
>>     desc->channel[i].pure_integer) ? TRUE : FALSE;
>>  }
>>
>> +boolean
>> +util_format_is_snorm(enum pipe_format format)
>> +{
>> +   const struct util_format_description *desc =
>> util_format_description(format);
>> +   int i;
>> +
>> +   i = util_format_get_first_non_void_channel(format);
>> +   if (i == -1)
>> +      return FALSE;
>> +
>> +   return desc->channel[i].type == UTIL_FORMAT_TYPE_SIGNED &&
>> +          !desc->channel[i].pure_integer &&
>> +          desc->channel[i].normalized;
>> +}
>
> This will give wrong results for mixed formats -- containing a mixture of SIGNED and UNSIGNED normalized types. You can avoid that by adding this statement
>
>   if (desc->is_mixed) return FALSE at the start.
>
> I think a comment would be good too -- something like "Returns true if all non-void channels are normalized signed."
>
> This is not your fault, but it is disappointing to see the proliferation of redundant util_format_description() calls in these helpers. util_format_description is not cost free, and st_CopyPixels and friends keep calling it over and over again. I don't think it is hard to call util_format_description() once, and then pass the format_desc pointers around, but once we start on the other route is hard to back out. But as they say -- when you're in a hole, the first thing to do is stop digging --, so I think we should just stop adding new helper functions to util u_format that take enum format instead of util_format_description.

I hestiate to say this as no doubt I'll be wrong, but if they are all
inline helpers, the compiler should figure it out and collapse the
lookups. Of course I believe compilers should do lots of things...

Dave.