#version 460
#extension GL_GOOGLE_include_directive : enable
#include "ui-shared.glsl"

// One workgroup per 8×8 screen tile. The workgroup cooperatively streams the
// ImageItem list in chunks of 64 (see ui-shared.glsl), culling each chunk
// against the tile and compacting survivors — in buffer order — into shared
// memory; every thread then accumulates over only those survivors.
layout(push_constant) uniform PC {
    UIDispatchHeader hdr;
} pc;

layout(local_size_x = 8, local_size_y = 8, local_size_z = 1) in;

shared vec4  s_rect[UI_CHUNK];
shared vec4  s_uv[UI_CHUNK];
shared vec4  s_tint[UI_CHUNK];
shared uvec4 s_slots[UI_CHUNK];
shared uint  s_keep[UI_CHUNK];
shared uint  s_order[UI_CHUNK];
shared uint  s_count;

void main() {
    ivec2 screenPx;
    bool  valid = uiResolveScreenPixel(pc.hdr, screenPx);

    vec4 dst = vec4(0.0);
    vec2 sp  = vec2(0.0);
    if (valid) {
        dst = imageLoad(uiImages[pc.hdr.outImage], screenPx);
        sp  = vec2(screenPx) + 0.5;
    }

    vec2 tileMin, tileMax;
    uiTileBounds(tileMin, tileMax);

    uint lid = gl_LocalInvocationIndex;
    for (uint base = 0u; base < pc.hdr.itemCount; base += UI_CHUNK) {
        uint idx  = base + lid;
        bool keep = false;
        if (idx < pc.hdr.itemCount) {
            s_rect[lid]  = uiImageHeap[pc.hdr.itemBuffer].items[idx].rect;
            s_uv[lid]    = uiImageHeap[pc.hdr.itemBuffer].items[idx].uv;
            s_tint[lid]  = uiImageHeap[pc.hdr.itemBuffer].items[idx].tint;
            s_slots[lid] = uiImageHeap[pc.hdr.itemBuffer].items[idx].slots;
            keep = uiAabbOverlapsTile(s_rect[lid].xy, s_rect[lid].xy + s_rect[lid].zw,
                                      tileMin, tileMax);
        }
        s_keep[lid] = keep ? 1u : 0u;
        barrier();

        if (lid == 0u) {
            uint n   = 0u;
            uint lim = min(UI_CHUNK, pc.hdr.itemCount - base);
            for (uint k = 0u; k < lim; ++k)
                if (s_keep[k] != 0u) s_order[n++] = k;
            s_count = n;
        }
        barrier();

        if (valid) {
            for (uint j = 0u; j < s_count; ++j) {
                uint c = s_order[j];

                vec2 lo = s_rect[c].xy;
                vec2 hi = s_rect[c].xy + s_rect[c].zw;
                if (sp.x < lo.x || sp.y < lo.y) continue;
                if (sp.x >= hi.x || sp.y >= hi.y) continue;

                vec2 t  = (sp - s_rect[c].xy) / s_rect[c].zw;
                vec2 uv = mix(s_uv[c].xy, s_uv[c].zw, t);

                uint texSlot  = s_slots[c].x;
                uint sampSlot = s_slots[c].y;

                vec4 sampled = texture(
                    sampler2D(uiTextures[nonuniformEXT(texSlot)],
                              uiSamplers[nonuniformEXT(sampSlot)]),
                    uv
                );
                vec4 src = sampled * s_tint[c];
                if (src.a <= 0.0) continue;
                dst = uiBlendOver(dst, src);
            }
        }
        barrier();
    }

    if (valid) imageStore(uiImages[pc.hdr.outImage], screenPx, dst);
}
