[Mesa-dev] TGSI and Tessellation Control Shader outputs

[Ilia Mirkin]

On Tue, Sep 16, 2014 at 12:29 PM, Marek Olšák <maraeo at gmail.com> wrote:
> On Tue, Sep 16, 2014 at 5:42 PM, Ilia Mirkin <imirkin at alum.mit.edu> wrote:
>> OK, so just to summarize:
>>
>> The approach suggested by Roland is to have the outputs be
>> one-dimensional and only representing the current invocation's
>> per-vertex outputs. Each invocation would also get access to other
>> invocations' per-vertex outputs via a 2d input array.
>>
>> So a shader might look something like
>>
>> TESSC
>> DECL IN[][0], POSITION (input patch's per-vertex position)
>> DECL IN[][1], GENERIC (input patch's per-vertex generic attribute)
>> DECL IN[][2], TCS_POSITION (output patch's per-vertex position)
>> DECL IN[][3], TCS_OUTPUT (output patch's per-vertex generic attribute)
>> DECL OUT[0], POSITION
>> DECL OUT[1], GENERIC
>> DECL OUT[2], PATCH
>>
>> And then anything written to OUT[0] would be aliased via IN[][2].
>> Roland, does that sound right? This seems kinda nasty that there are
>> going to be 2 types of position/pointsize/clipdistance inputs -- do
>> you have a better suggestion for handling that?
>
> The output-as-input arrays can be declared as system values (SV), then
> you don't need to duplicate semantic names.

OK, that sounds reasonable. And what do you guys think about reading
directly from per-patch outputs? Or should they also be mirrored as
SV's? We definitely need something since it's shared between
invocations and synchronizable using barrier.

  -ilia