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//! 2× box-filter downsample for half-resolution blur.
//!
//! Averages each 2×2 block of pixels into one output pixel.
//! Category A composition - pure IR. No Tier 2.5 primitives.
use vyre::ir::{BufferAccess, BufferDecl, DataType, Expr, Node, Program};
const OP_ID: &str = "vyre-libs::visual::downsample";
/// Build a Program that 2× downsamples `input` into `output`.
///
/// - `input`: `[u32; width * height]` - source pixels (packed RGBA)
/// - `output`: `[u32; (width/2) * (height/2)]` - downsampled result
/// - Width and height must be even.
#[must_use]
pub fn downsample_2x(input: &str, output: &str, width: u32, height: u32) -> Program {
let out_w = width / 2;
let out_h = height / 2;
let input_count = width.saturating_mul(height);
let output_count = out_w.saturating_mul(out_h);
Program::wrapped(
vec![
BufferDecl::storage(input, 0, BufferAccess::ReadOnly, DataType::U32)
.with_count(input_count),
BufferDecl::storage(output, 1, BufferAccess::ReadWrite, DataType::U32)
.with_count(output_count),
],
super::PIXEL_WORKGROUP_SIZE,
vec![crate::region::wrap_anonymous(
OP_ID,
vec![
Node::let_bind("idx", Expr::gid_x()),
Node::if_then(
Expr::lt(Expr::var("idx"), Expr::u32(output_count)),
vec![
Node::let_bind("ox", Expr::rem(Expr::var("idx"), Expr::u32(out_w.max(1)))),
Node::let_bind("oy", Expr::div(Expr::var("idx"), Expr::u32(out_w.max(1)))),
// Source pixel coordinates.
Node::let_bind("sx", Expr::mul(Expr::var("ox"), Expr::u32(2))),
Node::let_bind("sy", Expr::mul(Expr::var("oy"), Expr::u32(2))),
// Load 4 source pixels.
Node::let_bind(
"p00",
Expr::load(
input,
Expr::add(
Expr::mul(Expr::var("sy"), Expr::u32(width)),
Expr::var("sx"),
),
),
),
Node::let_bind(
"p10",
Expr::load(
input,
Expr::add(
Expr::mul(Expr::var("sy"), Expr::u32(width)),
Expr::add(Expr::var("sx"), Expr::u32(1)),
),
),
),
Node::let_bind(
"p01",
Expr::load(
input,
Expr::add(
Expr::mul(
Expr::add(Expr::var("sy"), Expr::u32(1)),
Expr::u32(width),
),
Expr::var("sx"),
),
),
),
Node::let_bind(
"p11",
Expr::load(
input,
Expr::add(
Expr::mul(
Expr::add(Expr::var("sy"), Expr::u32(1)),
Expr::u32(width),
),
Expr::add(Expr::var("sx"), Expr::u32(1)),
),
),
),
// Average each channel: (c0+c1+c2+c3+2) >> 2
// R channel
Node::let_bind(
"r",
Expr::shr(
Expr::add(
Expr::add(
Expr::add(
Expr::bitand(Expr::var("p00"), Expr::u32(0xFF)),
Expr::bitand(Expr::var("p10"), Expr::u32(0xFF)),
),
Expr::add(
Expr::bitand(Expr::var("p01"), Expr::u32(0xFF)),
Expr::bitand(Expr::var("p11"), Expr::u32(0xFF)),
),
),
Expr::u32(2),
),
Expr::u32(2),
),
),
// G channel
Node::let_bind(
"g",
Expr::shr(
Expr::add(
Expr::add(
Expr::add(
Expr::bitand(
Expr::shr(Expr::var("p00"), Expr::u32(8)),
Expr::u32(0xFF),
),
Expr::bitand(
Expr::shr(Expr::var("p10"), Expr::u32(8)),
Expr::u32(0xFF),
),
),
Expr::add(
Expr::bitand(
Expr::shr(Expr::var("p01"), Expr::u32(8)),
Expr::u32(0xFF),
),
Expr::bitand(
Expr::shr(Expr::var("p11"), Expr::u32(8)),
Expr::u32(0xFF),
),
),
),
Expr::u32(2),
),
Expr::u32(2),
),
),
// B channel
Node::let_bind(
"b",
Expr::shr(
Expr::add(
Expr::add(
Expr::add(
Expr::bitand(
Expr::shr(Expr::var("p00"), Expr::u32(16)),
Expr::u32(0xFF),
),
Expr::bitand(
Expr::shr(Expr::var("p10"), Expr::u32(16)),
Expr::u32(0xFF),
),
),
Expr::add(
Expr::bitand(
Expr::shr(Expr::var("p01"), Expr::u32(16)),
Expr::u32(0xFF),
),
Expr::bitand(
Expr::shr(Expr::var("p11"), Expr::u32(16)),
Expr::u32(0xFF),
),
),
),
Expr::u32(2),
),
Expr::u32(2),
),
),
// A channel
Node::let_bind(
"a",
Expr::shr(
Expr::add(
Expr::add(
Expr::add(
Expr::shr(Expr::var("p00"), Expr::u32(24)),
Expr::shr(Expr::var("p10"), Expr::u32(24)),
),
Expr::add(
Expr::shr(Expr::var("p01"), Expr::u32(24)),
Expr::shr(Expr::var("p11"), Expr::u32(24)),
),
),
Expr::u32(2),
),
Expr::u32(2),
),
),
// Pack RGBA.
Node::let_bind(
"packed",
Expr::bitor(
Expr::bitor(
Expr::var("r"),
Expr::shl(Expr::var("g"), Expr::u32(8)),
),
Expr::bitor(
Expr::shl(Expr::var("b"), Expr::u32(16)),
Expr::shl(Expr::var("a"), Expr::u32(24)),
),
),
),
// Write output.
Node::let_bind(
"oidx",
Expr::add(
Expr::mul(Expr::var("oy"), Expr::u32(out_w)),
Expr::var("ox"),
),
),
Node::store(output, Expr::var("oidx"), Expr::var("packed")),
],
),
],
)],
)
}
inventory::submit! {
crate::harness::OpEntry {
id: OP_ID,
build: || downsample_2x("input", "output", 4, 4),
test_inputs: Some(|| {
// 4×4 all-white → 2×2 all-white
let input = vec![0xFFFF_FFFFu32; 16];
vec![vec![
crate::visual::byte_helpers::u32_words_to_le_bytes(&input),
vec![0u8; 16],
]]
}),
expected_output: Some(|| {
let expected = vec![0xFFFF_FFFFu32; 4];
vec![vec![crate::visual::byte_helpers::u32_words_to_le_bytes(&expected)]]
}),
category: Some("visual"),
}
}