nir: Add new intrinsics for fragment shader input interpolation.

Backends can normally handle shader inputs solely by looking at
load_input intrinsics, and ignore the nir_variables in nir->inputs.

One exception is fragment shader inputs.  load_input doesn't capture
the necessary interpolation information - flat, smooth, noperspective
mode, and centroid, sample, or pixel for the location.  This means
that backends have to interpolate based on the nir_variables, then
associate those with the load_input intrinsics (say, by storing a
map of which variables are at which locations).

With GL_ARB_enhanced_layouts, we're going to have multiple varyings
packed into a single vec4 location.  The intrinsics make this easy:
simply load N components from location <loc, component>.  However,
working with variables and correlating the two is very awkward; we'd
much rather have intrinsics capture all the necessary information.

Fragment shader input interpolation typically works by producing a
set of barycentric coordinates, then using those to do a linear
interpolation between the values at the triangle's corners.

We represent this by introducing five new load_barycentric_* intrinsics:

- load_barycentric_pixel     (ordinary variable)
- load_barycentric_centroid  (centroid qualified variable)
- load_barycentric_sample    (sample qualified variable)
- load_barycentric_at_sample (ARB_gpu_shader5's interpolateAtSample())
- load_barycentric_at_offset (ARB_gpu_shader5's interpolateAtOffset())

Each of these take the interpolation mode (smooth or noperspective only)
as a const_index, and produce a vec2.  The last two also take a sample
or offset source.

We then introduce a new load_interpolated_input intrinsic, which
is like a normal load_input intrinsic, but with an additional
barycentric coordinate source.

The intention is that flat inputs will still use regular load_input
intrinsics.  This makes them distinguishable from normal inputs that
need fancy interpolation, while also providing all the necessary data.

This nicely unifies regular inputs and interpolateAt functions.
Qualifiers and variables become irrelevant; there are just
load_barycentric intrinsics that determine the interpolation.

v2: Document the interp_mode const_index value, define a new
    BARYCENTRIC() helper rather than using SYSTEM_VALUE() for
    some of them (requested by Jason Ekstrand).

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Chris Forbes <chrisforbes@google.com>
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>

diff --git a/src/compiler/nir/nir.h b/src/compiler/nir/nir.h
index c5d3b6b698d37bb4a941e63b3e9b2df6e4086755..ac119981ec9922f305a997b0cc0a4f22213d94fd 100644 (file)
--- a/src/compiler/nir/nir.h
+++ b/src/compiler/nir/nir.h
@@ -992,6 +992,11 @@ typedef enum {
     */
    NIR_INTRINSIC_COMPONENT = 8,
 
+   /**
+    * Interpolation mode (only meaningful for FS inputs).
+    */
+   NIR_INTRINSIC_INTERP_MODE = 9,
+
    NIR_INTRINSIC_NUM_INDEX_FLAGS,
 
 } nir_intrinsic_index_flag;
@@ -1059,6 +1064,7 @@ INTRINSIC_IDX_ACCESSORS(range, RANGE, unsigned)
 INTRINSIC_IDX_ACCESSORS(desc_set, DESC_SET, unsigned)
 INTRINSIC_IDX_ACCESSORS(binding, BINDING, unsigned)
 INTRINSIC_IDX_ACCESSORS(component, COMPONENT, unsigned)
+INTRINSIC_IDX_ACCESSORS(interp_mode, INTERP_MODE, unsigned)
 
 /**
  * \group texture information

diff --git a/src/compiler/nir/nir_builder.h b/src/compiler/nir/nir_builder.h
index 09cdf72bfffb08da0817875bea5ee75724cc70d1..435582aca3c2252410358326aef541c25854f8b4 100644 (file)
--- a/src/compiler/nir/nir_builder.h
+++ b/src/compiler/nir/nir_builder.h
@@ -458,6 +458,17 @@ nir_load_system_value(nir_builder *build, nir_intrinsic_op op, int index)
    return &load->dest.ssa;
 }
 
+static inline nir_ssa_def *
+nir_load_barycentric(nir_builder *build, nir_intrinsic_op op,
+                     unsigned interp_mode)
+{
+   nir_intrinsic_instr *bary = nir_intrinsic_instr_create(build->shader, op);
+   nir_ssa_dest_init(&bary->instr, &bary->dest, 2, 32, NULL);
+   nir_intrinsic_set_interp_mode(bary, interp_mode);
+   nir_builder_instr_insert(build, &bary->instr);
+   return &bary->dest.ssa;
+}
+
 static inline void
 nir_jump(nir_builder *build, nir_jump_type jump_type)
 {

diff --git a/src/compiler/nir/nir_intrinsics.h b/src/compiler/nir/nir_intrinsics.h
index 2f74555ee4878b0e7522f7851d6f13b40232ce3d..cf2ddc8ac72d2a87eedebc70972c1cb37ee3d276 100644 (file)
--- a/src/compiler/nir/nir_intrinsics.h
+++ b/src/compiler/nir/nir_intrinsics.h
@@ -306,6 +306,35 @@ SYSTEM_VALUE(num_work_groups, 3, 0, xx, xx, xx)
 SYSTEM_VALUE(helper_invocation, 1, 0, xx, xx, xx)
 SYSTEM_VALUE(channel_num, 1, 0, xx, xx, xx)
 
+/**
+ * Barycentric coordinate intrinsics.
+ *
+ * These set up the barycentric coordinates for a particular interpolation.
+ * The first three are for the simple cases: pixel, centroid, or per-sample
+ * (at gl_SampleID).  The next two handle interpolating at a specified
+ * sample location, or interpolating with a vec2 offset,
+ *
+ * The interp_mode index should be either the INTERP_MODE_SMOOTH or
+ * INTERP_MODE_NOPERSPECTIVE enum values.
+ *
+ * The vec2 value produced by these intrinsics is intended for use as the
+ * barycoord source of a load_interpolated_input intrinsic.
+ */
+
+#define BARYCENTRIC(name, sources, source_components) \
+   INTRINSIC(load_barycentric_##name, sources, ARR(source_components), \
+             true, 2, 0, 1, INTERP_MODE, xx, xx, \
+             NIR_INTRINSIC_CAN_ELIMINATE | NIR_INTRINSIC_CAN_REORDER)
+
+/* no sources.  const_index[] = { interp_mode } */
+BARYCENTRIC(pixel, 0, 0)
+BARYCENTRIC(centroid, 0, 0)
+BARYCENTRIC(sample, 0, 0)
+/* src[] = { sample_id }.  const_index[] = { interp_mode } */
+BARYCENTRIC(at_sample, 1, 1)
+/* src[] = { offset.xy }.  const_index[] = { interp_mode } */
+BARYCENTRIC(at_offset, 1, 2)
+
 /*
  * Load operations pull data from some piece of GPU memory.  All load
  * operations operate in terms of offsets into some piece of theoretical
@@ -339,6 +368,9 @@ LOAD(ubo, 2, 0, xx, xx, xx, NIR_INTRINSIC_CAN_ELIMINATE | NIR_INTRINSIC_CAN_REOR
 LOAD(input, 1, 2, BASE, COMPONENT, xx, NIR_INTRINSIC_CAN_ELIMINATE | NIR_INTRINSIC_CAN_REORDER)
 /* src[] = { vertex, offset }. const_index[] = { base, component } */
 LOAD(per_vertex_input, 2, 2, BASE, COMPONENT, xx, NIR_INTRINSIC_CAN_ELIMINATE | NIR_INTRINSIC_CAN_REORDER)
+/* src[] = { barycoord, offset }. const_index[] = { base, component } */
+LOAD(interpolated_input, 2, 2, BASE, COMPONENT, xx, NIR_INTRINSIC_CAN_ELIMINATE | NIR_INTRINSIC_CAN_REORDER)
+
 /* src[] = { buffer_index, offset }. No const_index */
 LOAD(ssbo, 2, 0, xx, xx, xx, NIR_INTRINSIC_CAN_ELIMINATE)
 /* src[] = { offset }. const_index[] = { base, component } */

diff --git a/src/compiler/nir/nir_lower_io.c b/src/compiler/nir/nir_lower_io.c
index 189370df3649c252cfe03cfe93b85556ce21cf38..9c1096179b165093789873dcfc58b78827a96735 100644 (file)
--- a/src/compiler/nir/nir_lower_io.c
+++ b/src/compiler/nir/nir_lower_io.c
@@ -436,6 +436,7 @@ nir_get_io_offset_src(nir_intrinsic_instr *instr)
    case nir_intrinsic_load_ssbo:
    case nir_intrinsic_load_per_vertex_input:
    case nir_intrinsic_load_per_vertex_output:
+   case nir_intrinsic_load_interpolated_input:
    case nir_intrinsic_store_output:
       return &instr->src[1];
    case nir_intrinsic_store_ssbo:

diff --git a/src/compiler/nir/nir_print.c b/src/compiler/nir/nir_print.c
index a3380e677d1c88862f2315010fbeb8ed1409180d..3beb70a75d31ee71b76af40a1af207805135dbf8 100644 (file)
--- a/src/compiler/nir/nir_print.c
+++ b/src/compiler/nir/nir_print.c
@@ -571,6 +571,7 @@ print_intrinsic_instr(nir_intrinsic_instr *instr, print_state *state)
       [NIR_INTRINSIC_DESC_SET] = "desc-set",
       [NIR_INTRINSIC_BINDING] = "binding",
       [NIR_INTRINSIC_COMPONENT] = "component",
+      [NIR_INTRINSIC_INTERP_MODE] = "interp_mode",
    };
    for (unsigned idx = 1; idx < NIR_INTRINSIC_NUM_INDEX_FLAGS; idx++) {
       if (!info->index_map[idx])