This VS system value will contain the value passed as <basevertex> for
indexed draw calls or the value passed as <first> for non-indexed draw
calls. It can be used to calculate the gl_VertexID as
SYSTEM_VALUE_VERTEX_ID_ZERO_BASE plus SYSTEM_VALUE_FIRST_VERTEX.
From the OpenGL 4.6 spec, 10.4 "Drawing Commands Using Vertex Arrays":
- Page 352:
"The index of any element transferred to the GL by DrawArraysOneInstance
is referred to as its vertex ID, and may be read by a vertex shader as
gl_VertexID. The vertex ID of the ith element transferred is first +
i."
- Page 355:
"The index of any element transferred to the GL by
DrawElementsOneInstance is referred to as its vertex ID, and may be read
by a vertex shader as gl_VertexID. The vertex ID of the ith element
transferred is the sum of basevertex and the value stored in the
currently bound element array buffer at offset indices + i."
Currently the gl_VertexID calculation uses SYSTEM_VALUE_BASE_VERTEX but
this will have to change when the value of gl_BaseVertex is
fixed. Currently its value is broken for non-indexed draw calls because
it must be zero but we are setting it to <first>.
v2: use SYSTEM_VALUE_FIRST_VERTEX as name for the value, instead of
SYSTEM_VALUE_BASE_VERTEX_ID (Kenneth).
v3 (idr): Rebase on Rob Clark converting nir_intrinsics.h to be
generated. Reformat commit message to 72 columns.
Reviewed-by: Neil Roberts <nroberts@igalia.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
I threatened to do this a long time ago.. I probably *should* have done
it a long time ago when there where many fewer intrinsics. But the
system of macro/#include magic for dealing with intrinsics is a bit
annoying, and python has the nice property of optional fxn params,
making it possible to define new intrinsics while ignoring parameters
that are not applicable (and naming optional params). And not having to
specify various array lengths explicitly is nice too.
I think the end result makes it easier to add new intrinsics.
v2: couple small fixes found with a test program to compare the old and
new tables
v3: misc comments, don't rely on capture=true for meson.build, get rid
of system_values table to avoid return value of intrinsic() and
*mostly* remove side-effects, add autotools build support
v4: scons build
Signed-off-by: Rob Clark <robdclark@gmail.com>
Acked-by: Dylan Baker <dylan@pnwbakers.com>
Acked-by: Jason Ekstrand <jason@jlekstrand.net>
