[Mesa-dev] [PATCH 3/3] r600g: implement fragment and vertex color clamp

[Alex Deucher]

On Mon, Jun 27, 2011 at 9:32 AM, Jerome Glisse <j.glisse at gmail.com> wrote:
> On Mon, Jun 27, 2011 at 8:38 AM, Roland Scheidegger <sroland at vmware.com> wrote:
>> Am 25.06.2011 00:22, schrieb Vadim Girlin:
>>> On 06/24/2011 11:38 PM, Jerome Glisse wrote:
>>>> On Fri, Jun 24, 2011 at 12:29 PM, Vadim Girlin<vadimgirlin at gmail.com>
>>>> wrote:
>>>>> Fixes https://bugs.freedesktop.org/show_bug.cgi?id=38440
>>>>>
>>>>> Signed-off-by: Vadim Girlin<vadimgirlin at gmail.com>
>>>>
>>>> As discussed previously, there is better to handle this. I think best
>>>> solution is to always add the instruction and to conditionally execute
>>>> them thanks to the boolean constant. If this reveal to have a too big
>>>> impact on shader, other solution i see is adding a cf block with those
>>>> instructions and to enable or disable that block (cf_nop) and reupload
>>>> shader that would avoid a rebuild.
>>>
>>> I know its not optimal to do a full rebuild, but rebuild is needed only
>>> when the application will use the same shader in different clamping
>>> states. It won't be a problem if the application doesn't change clamping
>>> state or if it changes the state but uses each shader in one state only.
>>> So assuming that typical app will not use one shader in both states, it
>>> shouldn't be a problem. Is this assumption wrong? I'm not really sure
>>> because I have no much experience in this. But if it's wrong then it's
>>> probably better for performance to build and cache both versions.
>> I tend to think you're right apps probably don't want to use the same
>> shader both with and without clamping.
>
> Well if boolean block (see COND field set to SQ_CF_COND_BOOL in
> SQ_CF_WORD1) are free from perf point of view then i think it's best
> to have one shader with the clamp instruction inside the boolean
> enabled block. Only benchmark can tell.

We could also cache recently used shaders rather than recompiling every time.

Alex