IfcOpenShell/src/ifcviewer/SidecarCache.h

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// NOTE: Sidecar format v3 is being rewritten to v4 (instanced geometry layout).
// During the instancing rewrite (Commit A) the cache is a no-op: reads always
// miss and writes always succeed without producing a file. Commit B will
// re-introduce the on-disk format with MeshInfo + InstanceGpu sections.

#ifndef SIDECARCACHE_H
#define SIDECARCACHE_H

#include "InstancedGeometry.h"

#include <cstdint>
#include <optional>
#include <string>
#include <vector>
#include <memory>

static constexpr uint32_t SIDECAR_MAGIC   = 0x49465657;  // "IFVW"
// v5 = MeshInfo extended with lod1_ebo_byte_offset + lod1_index_count (56 B).
//      sd.indices may contain an appended LOD1 index slice for each mesh
//      where meshoptimizer decimation produced useful output.
// v6 = VBO vertices quantized to 16 B/vertex (pos u16x3 + normal oct i16x2 +
//      color u8x4).  Dequant basis is per-mesh MeshInfo.local_aabb_min/max.
// v7 = VBO vertices shrunk to 12 B/vertex (normal oct i8x2 replaces i16x2,
//      eliminating 2-byte pad + saving 2 bytes on normal).
// v8 = source_file_size field dropped from header.  Sidecar is keyed purely
//      on path stem (foo.ifc and foo.ifcdb/ both map to foo.ifcview) so the
//      same cache serves either source format.  Staleness is user-managed
//      (delete the sidecar to force a rebuild).
// v9 = unused `reserved` field dropped from header (16 B -> 12 B).
// v10 = InstanceCpu gains placement_transformation[16] alongside transform[16]
//       — record grew from 104 B to 168 B.  placement_transformation is the
//       raw streamer output; transform is the composed FederatedFalseOrigin ·
//       ModelTransformation · CoordinateOperation · placement_transformation
//       result.  Sidecar serialises both; on load the transform is recomputed
//       from placement_transformation + the ViewportWindow's current stage
//       matrices, so v10 sidecars are reusable across .ifcfeds.
// v11 = SidecarData gains a per-model CoordinateOperation cache:
//       coordinate_operation_meters[16] (column-major), unit scales, and a
//       has_coordinate_operation flag.  Lets sidecar-loaded models apply
//       georef without re-parsing the IFC source.  Edits to the IFC's
//       IfcMapConversion do NOT invalidate the sidecar — delete the
//       .ifcview manually if you change the source's georef parameters.
// v12 = InstanceCpu::placement_transformation is double[16], and
//       InstanceChunk carries the streamer placement as double[16].  This keeps
//       large IFC placements exact until CoordinateOperation / FederatedFalseOrigin
//       composition has reduced them to viewport-local float-sized values.
// v13 = Map unit scale in cached ModelGeoref is derived from
//       IfcMapConversion.Scale, not IfcProjectedCRS.MapUnit.
// v14 = Geometry is laid out in streaming-chunk order (SidecarLayout) and a
//       chunk table-of-contents (`chunks`) is appended.  The loader builds its
//       chunks from the TOC instead of re-deriving the Morton/greedy plan, so
//       each chunk is one CONTIGUOUS byte range — fixing network read
//       amplification.  The plan can't be re-derived at load because the float
//       Morton quantisation isn't bit-identical across toolchains (x86 baker vs
//       wasm loader), so it must be baked in.  No back-compat: v13 sidecars are
//       rejected (regenerate them).
// v15 = The post-index metadata is split into a render-CRITICAL block (meshes,
//       instances, georef, chunk TOC) followed by a DEFERRED block (elements +
//       string_table — the IFC element tree, used for UI/picking, never for
//       rendering), with the critical block's byte length written just after
//       the index section.  The web loader reads only the critical block before
//       painting, so first geometry no longer waits on the property data; the
//       deferred block is fetched lazily (or skipped where unused).  Desktop
//       reads both.  No back-compat: regenerate sidecars.
// v16 = Geometry + metadata are zstd-COMPRESSED.  Each chunk's vertex bytes and
//       index bytes are stored as two independent zstd frames (so per-chunk
//       Range streaming still works — you fetch + decompress just one chunk),
//       and the critical + deferred metadata blocks are single zstd frames.
//       The chunk TOC records each chunk's compressed blob offsets/sizes plus
//       the raw (decompressed) sizes.  ~3-5x fewer bytes over the wire while
//       keeping HTTP Range intact (unlike server Content-Encoding).  No
//       back-compat: regenerate sidecars.
static constexpr uint32_t SIDECAR_VERSION = 16;
static constexpr uint32_t SIDECAR_ENDIAN  = 0x01020304;

// Chunk table-of-contents entry (v16).  A chunk is a CONTIGUOUS range of meshes
// [first_mesh, first_mesh + mesh_count).  Its vertex + index bytes are stored as
// two zstd frames in the geometry section; the loader fetches [v_comp_off,
// +v_comp_size) / [i_comp_off, +i_comp_size) (offsets relative to the geometry
// section start) and decompresses them to v_raw_size / i_raw_size bytes — the
// chunk-local (vbytes, idx) applyStreamedChunk consumes.
struct SidecarChunk {
    uint32_t first_mesh;
    uint32_t mesh_count;
    uint64_t v_comp_off;
    uint64_t v_comp_size;
    uint64_t v_raw_size;
    uint64_t i_comp_off;
    uint64_t i_comp_size;
    uint64_t i_raw_size;
};

// Fixed-size element record.  Strings are stored as (offset, length) pairs
// into a separate string table.
struct PackedElementInfo {
    uint32_t object_id;
    uint32_t model_id;
    int32_t  ifc_id;
    int32_t  parent_id;
    uint32_t guid_offset;
    uint32_t guid_length;
    uint32_t name_offset;
    uint32_t name_length;
    uint32_t type_offset;
    uint32_t type_length;
};

// Everything needed to display an already-tessellated model without
// re-running the iterator.  v6 schema: instanced + quantized geometry.
struct SidecarData {
    // Per-model GPU geometry (local coords).  Raw VBO bytes at the
    // INSTANCED_VERTEX_STRIDE_BYTES layout (12 B/vertex as of v7).
    std::vector<uint8_t>      vertices;
    std::vector<uint32_t>     indices;

    // Mesh dictionary and per-instance data.
    std::vector<MeshInfo>     meshes;        // indexed by local_mesh_id
    std::vector<InstanceCpu>  instances;     // sorted by mesh_id

    // CoordinateOperation cache (v11+).  Mirrors ModelGeoref so a sidecar
    // load can apply georef without re-parsing the IFC source.
    // has_coordinate_operation == 0 means the model has no
    // IfcMapConversion; the matrix is then the identity placeholder.
    double   coordinate_operation_meters[16] = {
                 1, 0, 0, 0,
                 0, 1, 0, 0,
                 0, 0, 1, 0,
                 0, 0, 0, 1 };
    double   project_length_to_meters = 1.0;
    double   map_unit_to_meters       = 1.0;
    uint32_t has_coordinate_operation = 0;

    // Element tree metadata.
    std::vector<PackedElementInfo> elements;
    std::string               string_table;

    // Streaming chunk TOC.  Always written on disk (v14); geometry is laid out
    // in this chunk order (see SidecarLayout) so each chunk is one contiguous
    // range and the loader builds chunks directly from it. Stays empty only for
    // in-memory direct loads (finalizeModel), which don't stream and fall back
    // to deriving the plan.
    std::vector<SidecarChunk> chunks;
};

// Sidecar is keyed on the path stem: foo.ifc and foo.ifcdb/ both resolve to
// foo.ifcview alongside the source.  No staleness check — callers delete the
// file to invalidate.
bool writeSidecar(const std::string& ifc_path, const SidecarData& data);

std::optional<SidecarData> readSidecar(const std::string& ifc_path);

#endif // SIDECARCACHE_H