Hi Roland,
It depends on the hardware. On Radeon, the tessellation evaluation
shader can read vertex shader outputs directly. That means the
tessellation control shader is not necessary if the tessellation
levels are fixed. set_tess_state sets the fixed tessellation levels
for exactly this case.
Other hardware may need to generate a pass-through tessellation
control shader and upload these parameters as constants for the shader
to use them.
Marek
On Mon, May 4, 2015 at 1:29 PM, Roland Scheidegger <srol...@vmware.com> wrote:
> Seems a bit awkward that you have to set such state separately. I don't
> know much about how this is supposed to work though, some quick grep
> says these parameters are used when there's no tessellation control
> shader, so I guess that's why it is separate state.
> How does that actually work in hw, can you just switch tesselation
> control shaders off or do you have to provide some kind of a default
> tesselation ctrl shader?
>
> Roland
>
> Am 02.05.2015 um 22:16 schrieb Ilia Mirkin:
>> Signed-off-by: Ilia Mirkin <imir...@alum.mit.edu>
>> ---
>> src/gallium/docs/source/context.rst | 5 +++++
>> src/gallium/include/pipe/p_context.h | 4 ++++
>> 2 files changed, 9 insertions(+)
>>
>> diff --git a/src/gallium/docs/source/context.rst
>> b/src/gallium/docs/source/context.rst
>> index 5861f46..0908ee7 100644
>> --- a/src/gallium/docs/source/context.rst
>> +++ b/src/gallium/docs/source/context.rst
>> @@ -79,6 +79,11 @@ objects. They all follow simple, one-method binding
>> calls, e.g.
>> should be the same as the number of set viewports and can be up to
>> PIPE_MAX_VIEWPORTS.
>> * ``set_viewport_states``
>> +* ``set_tess_state`` configures the default tessellation parameters:
>> + * ``default_outer_level`` is the default value for the outer tessellation
>> + levels. This corresponds to GL's ``PATCH_DEFAULT_OUTER_LEVEL``.
>> + * ``default_inner_level`` is the default value for the inner tessellation
>> + levels. This corresponds to GL's ``PATCH_DEFAULT_INNER_LEVEL``.
>>
>>
>> Sampler Views
>> diff --git a/src/gallium/include/pipe/p_context.h
>> b/src/gallium/include/pipe/p_context.h
>> index 74c2f2f..afc5d7b 100644
>> --- a/src/gallium/include/pipe/p_context.h
>> +++ b/src/gallium/include/pipe/p_context.h
>> @@ -231,6 +231,10 @@ struct pipe_context {
>> unsigned start_slot, unsigned num_views,
>> struct pipe_sampler_view **);
>>
>> + void (*set_tess_state)(struct pipe_context *,
>> + float default_outer_level[4],
>> + float default_inner_level[2]);
>> +
>> /**
>> * Bind an array of shader resources that will be used by the
>> * graphics pipeline. Any resources that were previously bound to
>>
>
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