vello/piet-gpu/shader/draw_leaf.comp

// SPDX-License-Identifier: Apache-2.0 OR MIT OR Unlicense

// The leaf scan pass for draw tag scan implemented as a tree reduction.
// This stage can be fused with its consumer but is separate now.


#version 450
#extension GL_GOOGLE_include_directive : enable

#include "mem.h"
#include "setup.h"

#define N_ROWS 8
#define LG_WG_SIZE 9
#define WG_SIZE (1 << LG_WG_SIZE)
#define PARTITION_SIZE (WG_SIZE * N_ROWS)

layout(local_size_x = WG_SIZE, local_size_y = 1) in;

layout(binding = 1) readonly buffer ConfigBuf {
    Config conf;
};

layout(binding = 2) readonly buffer SceneBuf {
    uint[] scene;
};

#include "scene.h"
#include "tile.h"
#include "drawtag.h"

#define Monoid DrawMonoid

layout(set = 0, binding = 3) readonly buffer ParentBuf {
    Monoid[] parent;
};

shared Monoid sh_scratch[WG_SIZE];

void main() {
    Monoid local[N_ROWS];

    uint ix = gl_GlobalInvocationID.x * N_ROWS;
    ElementRef ref = ElementRef(ix * Element_size);
    uint tag_word = Element_tag(ref).tag;

    Monoid agg = map_tag(tag_word);
    local[0] = agg;
    for (uint i = 1; i < N_ROWS; i++) {
        tag_word = Element_tag(Element_index(ref, i)).tag;
        agg = combine_tag_monoid(agg, map_tag(tag_word));
        local[i] = agg;
    }
    sh_scratch[gl_LocalInvocationID.x] = agg;
    for (uint i = 0; i < LG_WG_SIZE; i++) {
        barrier();
        if (gl_LocalInvocationID.x >= (1u << i)) {
            Monoid other = sh_scratch[gl_LocalInvocationID.x - (1u << i)];
            agg = combine_tag_monoid(other, agg);
        }
        barrier();
        sh_scratch[gl_LocalInvocationID.x] = agg;
    }
    
    barrier();
    Monoid row = tag_monoid_identity();
    if (gl_WorkGroupID.x > 0) {
        row = parent[gl_WorkGroupID.x - 1];
    }
    if (gl_LocalInvocationID.x > 0) {
        row = combine_tag_monoid(row, sh_scratch[gl_LocalInvocationID.x - 1]);
    }
    uint out_base = (conf.drawmonoid_alloc.offset >> 2) + gl_GlobalInvocationID.x * 2 * N_ROWS;
    for (uint i = 0; i < N_ROWS; i++) {
        Monoid m = combine_tag_monoid(row, local[i]);
        memory[out_base + i * 2] = m.path_ix;
        memory[out_base + i * 2 + 1] = m.clip_ix;
    }
}