FWIW nvidia also does not require a special TCS in this case and can program the tessellation levels directly from the cmd stream. [Actually it might need a TCS with only an "exit" instruction, I should double-check.] However AFAIK Intel hardware requires a more involved passthrough TCS which handles setting the levels and potentially copying the per-vertex values over, not sure about the latter bit. Here is the nvc0 impl:
https://github.com/imirkin/mesa/commit/3b7b3887f2dc106305efc3b49b295551e24d2790#diff-21f2776e5f66dfdae77438adc195ba2aR539 On Mon, May 4, 2015 at 9:33 AM, Marek Olšák <mar...@gmail.com> wrote: > 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 >>> >> >> _______________________________________________ >> mesa-dev mailing list >> mesa-dev@lists.freedesktop.org >> http://lists.freedesktop.org/mailman/listinfo/mesa-dev _______________________________________________ mesa-dev mailing list mesa-dev@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/mesa-dev
