lampshade 0.13.0

Fast, composable GPU primitives for Rust applications using wgpu and WGSL.
Documentation 
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struct Params {
    num_items: u32,
    groups_x: u32,
    scan_items_per_block: u32,
    _padding_1: u32,
}

struct KeyValue {
    key: u32,
    value: u32,
}

@group(0) @binding(0) var<storage, read> input: array<{{ITEM_TYPE}}>;
@group(0) @binding(1) var<storage, read> mask: array<u32>;
@group(0) @binding(2) var<storage, read> offsets: array<u32>;
@group(0) @binding(3) var<storage, read_write> output: array<{{ITEM_TYPE}}>;
@group(0) @binding(4) var<storage, read_write> output_count: array<u32>;
@group(0) @binding(5) var<storage, read> block_prefixes: array<u32>;
@group(0) @binding(6) var<uniform> params: Params;

const BLOCK_SIZE: u32 = 256u;

@compute @workgroup_size(BLOCK_SIZE)
fn main(
    @builtin(workgroup_id) group_id: vec3<u32>,
    @builtin(local_invocation_id) local_id: vec3<u32>,
) {
    let flat_group_id = group_id.y * params.groups_x + group_id.x;
    let index = flat_group_id * BLOCK_SIZE + local_id.x;
    if (index >= params.num_items) {
        return;
    }

    let keep = mask[index];
    let scan_block = index / params.scan_items_per_block;
    var destination = offsets[index];
    if (scan_block > 0u) {
        destination += block_prefixes[scan_block - 1u];
    }
    if (keep == 1u) {
        output[destination] = input[index];
    }

    if (index + 1u == params.num_items) {
        output_count[0] = destination + keep;
    }
}