[Mesa-dev] [PATCH 3/8] glsl: use dual slot helper in the linker code.

[Dave Airlie]

On 9 December 2015 at 21:39, Timothy Arceri <t_arceri at yahoo.com.au> wrote:
> On Wed, 2015-12-09 at 16:06 +1000, Dave Airlie wrote:
>> From: Dave Airlie <airlied at redhat.com>
>>
>> Signed-off-by: Dave Airlie <airlied at redhat.com>
>
> Great timing :) I was going to have to look into fixing this stuff for
> enhanced layouts.
>
> Patches 1 & 2 are:
> Reviewed-by: Timothy Arceri <timothy.arceri at collabora.com>
>
> I have a question about this patch. If these doubles only take up a
> single attribute then why do we even bother with this test? The spec
> says its optional and your fixing the counting up in later patches so
> what does it do thats useful?

It's complicated.

ARB_gpu_shader_fp64 passes doubles between shaders, dual slots ones
take two locations. So a dvec3[2] will consume locations 17/18, 19/20.
The limits
are in number of locations.

ARB_vertex_attrib_64bit allows doubles as vertex inputs. Dual slot ones
take up a single location, however they consume two slots with respect
to the hw limits. So a dvec3[2] will consume 17, 18. However it will take
4 slots against the vertex attrib limits.

Dave.