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 <nrobe...@igalia.com>
Reviewed-by: Kenneth Graunke <kenn...@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
*
--
2.14.1
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