v3d/compiler: support swapping R/B channels in vertex attributes.
We will need this in Vulkan to support vertex format
VK_FORMAT_B8G8R8A8_UNORM. The hardware doesn't allow to swizzle
vertex attribute components, so we need to do it in the shader.
v2:
- Use nir_intrinsic_io_semantics() to retrieve the location instead
of looping through the shader input variables (Eric).
- Assert that we only have one component (Eric).
Reviewed-by: Alejandro PiƱeiro <apinheiro@igalia.com> (v1)
Reviewed-by: Eric Anholt <eric@anholt.net>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6766>
diff --git a/src/broadcom/compiler/v3d_compiler.h b/src/broadcom/compiler/v3d_compiler.h
index e17aa4c..5f0e83c 100644
--- a/src/broadcom/compiler/v3d_compiler.h
+++ b/src/broadcom/compiler/v3d_compiler.h
@@ -412,6 +412,12 @@
struct v3d_varying_slot used_outputs[V3D_MAX_ANY_STAGE_INPUTS];
uint8_t num_used_outputs;
+ /* A bit-mask indicating if we need to swap the R/B channels for
+ * vertex attributes. Since the hardware doesn't provide any
+ * means to swizzle vertex attributes we need to do it in the shader.
+ */
+ uint16_t va_swap_rb_mask;
+
bool is_coord;
bool per_vertex_point_size;
bool clamp_color;
diff --git a/src/broadcom/compiler/v3d_nir_lower_io.c b/src/broadcom/compiler/v3d_nir_lower_io.c
index 9242460..baf745c 100644
--- a/src/broadcom/compiler/v3d_nir_lower_io.c
+++ b/src/broadcom/compiler/v3d_nir_lower_io.c
@@ -333,6 +333,34 @@
nir_instr_remove(&instr->instr);
}
+/* Some vertex attribute formats may require to apply a swizzle but the hardware
+ * doesn't provide means to do that, so we need to apply the swizzle in the
+ * vertex shader.
+ *
+ * This is required at least in Vulkan to support madatory vertex attribute
+ * format VK_FORMAT_B8G8R8A8_UNORM.
+ */
+static void
+v3d_nir_lower_vertex_input(struct v3d_compile *c, nir_builder *b,
+ nir_intrinsic_instr *instr)
+{
+ assert(c->s->info.stage == MESA_SHADER_VERTEX);
+
+ if (!c->vs_key->va_swap_rb_mask)
+ return;
+
+ const uint32_t location =
+ nir_intrinsic_io_semantics(instr).location - VERT_ATTRIB_GENERIC0;
+ assert(location < V3D_MAX_VS_INPUTS / 4);
+ if (!(c->vs_key->va_swap_rb_mask & (1 << location)))
+ return;
+
+ assert(instr->num_components == 1);
+ const uint32_t comp = nir_intrinsic_component(instr);
+ if (comp == 0 || comp == 2)
+ nir_intrinsic_set_component(instr, (comp + 2) % 4);
+}
+
static void
v3d_nir_lower_io_instr(struct v3d_compile *c, nir_builder *b,
struct nir_instr *instr,
@@ -343,6 +371,11 @@
nir_intrinsic_instr *intr = nir_instr_as_intrinsic(instr);
switch (intr->intrinsic) {
+ case nir_intrinsic_load_input:
+ if (c->s->info.stage == MESA_SHADER_VERTEX)
+ v3d_nir_lower_vertex_input(c, b, intr);
+ break;
+
case nir_intrinsic_load_uniform:
v3d_nir_lower_uniform(c, b, intr);
break;