[Mesa-dev] [PATCH v3 2/8] compiler: Add SYSTEM_VALUE_FIRST_VERTEX and instrinsics

[Antia Puentes]

This series is still waiting for review.


On 25/01/18 19:15, Antia Puentes wrote:
> 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).
>
> Reviewed-by: Neil Roberts <nroberts at igalia.com>
> Reviewed-by: Kenneth Graunke <kenneth at whitecape.org>
> ---
>   src/compiler/nir/nir.c             |  4 ++++
>   src/compiler/nir/nir_gather_info.c |  1 +
>   src/compiler/nir/nir_intrinsics.h  |  1 +
>   src/compiler/shader_enums.c        |  1 +
>   src/compiler/shader_enums.h        | 14 ++++++++++++++
>   5 files changed, 21 insertions(+)
>
> diff --git a/src/compiler/nir/nir.c b/src/compiler/nir/nir.c
> index bdd8960403c..e69c2accbbf 100644
> --- a/src/compiler/nir/nir.c
> +++ b/src/compiler/nir/nir.c
> @@ -1919,6 +1919,8 @@ nir_intrinsic_from_system_value(gl_system_value val)
>         return nir_intrinsic_load_base_instance;
>      case SYSTEM_VALUE_VERTEX_ID_ZERO_BASE:
>         return nir_intrinsic_load_vertex_id_zero_base;
> +   case SYSTEM_VALUE_FIRST_VERTEX:
> +      return nir_intrinsic_load_first_vertex;
>      case SYSTEM_VALUE_BASE_VERTEX:
>         return nir_intrinsic_load_base_vertex;
>      case SYSTEM_VALUE_INVOCATION_ID:
> @@ -1990,6 +1992,8 @@ nir_system_value_from_intrinsic(nir_intrinsic_op intrin)
>         return SYSTEM_VALUE_BASE_INSTANCE;
>      case nir_intrinsic_load_vertex_id_zero_base:
>         return SYSTEM_VALUE_VERTEX_ID_ZERO_BASE;
> +   case nir_intrinsic_load_first_vertex:
> +      return SYSTEM_VALUE_FIRST_VERTEX;
>      case nir_intrinsic_load_base_vertex:
>         return SYSTEM_VALUE_BASE_VERTEX;
>      case nir_intrinsic_load_invocation_id:
> diff --git a/src/compiler/nir/nir_gather_info.c b/src/compiler/nir/nir_gather_info.c
> index 946939657ec..555ae77b1d3 100644
> --- a/src/compiler/nir/nir_gather_info.c
> +++ b/src/compiler/nir/nir_gather_info.c
> @@ -247,6 +247,7 @@ gather_intrinsic_info(nir_intrinsic_instr *instr, nir_shader *shader)
>      case nir_intrinsic_load_vertex_id:
>      case nir_intrinsic_load_vertex_id_zero_base:
>      case nir_intrinsic_load_base_vertex:
> +   case nir_intrinsic_load_first_vertex:
>      case nir_intrinsic_load_base_instance:
>      case nir_intrinsic_load_instance_id:
>      case nir_intrinsic_load_sample_id:
> diff --git a/src/compiler/nir/nir_intrinsics.h b/src/compiler/nir/nir_intrinsics.h
> index ede29277876..7d3421f0e30 100644
> --- a/src/compiler/nir/nir_intrinsics.h
> +++ b/src/compiler/nir/nir_intrinsics.h
> @@ -333,6 +333,7 @@ SYSTEM_VALUE(frag_coord, 4, 0, xx, xx, xx)
>   SYSTEM_VALUE(front_face, 1, 0, xx, xx, xx)
>   SYSTEM_VALUE(vertex_id, 1, 0, xx, xx, xx)
>   SYSTEM_VALUE(vertex_id_zero_base, 1, 0, xx, xx, xx)
> +SYSTEM_VALUE(first_vertex, 1, 0, xx, xx, xx)
>   SYSTEM_VALUE(base_vertex, 1, 0, xx, xx, xx)
>   SYSTEM_VALUE(instance_id, 1, 0, xx, xx, xx)
>   SYSTEM_VALUE(base_instance, 1, 0, xx, xx, xx)
> diff --git a/src/compiler/shader_enums.c b/src/compiler/shader_enums.c
> index 2179c475abd..5e123f29f37 100644
> --- a/src/compiler/shader_enums.c
> +++ b/src/compiler/shader_enums.c
> @@ -214,6 +214,7 @@ gl_system_value_name(gl_system_value sysval)
>        ENUM(SYSTEM_VALUE_INSTANCE_ID),
>        ENUM(SYSTEM_VALUE_INSTANCE_INDEX),
>        ENUM(SYSTEM_VALUE_VERTEX_ID_ZERO_BASE),
> +     ENUM(SYSTEM_VALUE_FIRST_VERTEX),
>        ENUM(SYSTEM_VALUE_BASE_VERTEX),
>        ENUM(SYSTEM_VALUE_BASE_INSTANCE),
>        ENUM(SYSTEM_VALUE_DRAW_ID),
> diff --git a/src/compiler/shader_enums.h b/src/compiler/shader_enums.h
> index ffe551ab20f..9f71194c146 100644
> --- a/src/compiler/shader_enums.h
> +++ b/src/compiler/shader_enums.h
> @@ -472,6 +472,20 @@ typedef enum
>       */
>      SYSTEM_VALUE_BASE_VERTEX,
>   
> +   /**
> +    * Depending on the type of the draw call (indexed or non-indexed),
> +    * is the value of \c basevertex passed to \c glDrawElementsBaseVertex and
> +    * similar, or is the value of \c first passed to \c glDrawArrays and
> +    * similar.
> +    *
> +    * \note
> +    * It can be used to calculate the \c SYSTEM_VALUE_VERTEX_ID as
> +    * \c SYSTEM_VALUE_VERTEX_ID_ZERO_BASE plus \c SYSTEM_VALUE_FIRST_VERTEX.
> +    *
> +    * \sa SYSTEM_VALUE_VERTEX_ID_ZERO_BASE, SYSTEM_VALUE_VERTEX_ID
> +    */
> +   SYSTEM_VALUE_FIRST_VERTEX,
> +
>      /**
>       * Value of \c baseinstance passed to instanced draw entry points
>       *