Crafter.Asset/interfaces/Crafter.Asset-Compression.cppm

//SPDX-License-Identifier: LGPL-3.0-only
//SPDX-FileCopyrightText: Copyright (C) 2026 Catcrafts®

export module Crafter.Asset:Compression;
import std;

export namespace Crafter::Compression {
    // Hard-aborts the process after printing `msg`. Used in place of
    // `throw std::runtime_error(...)` so the module is buildable under
    // `-fno-exceptions` (wasm targets ship without the C++ unwinding
    // runtime). Asset-loading errors are unrecoverable in practice — a
    // bad magic, version mismatch, or stream-size mismatch always means
    // the build's data is inconsistent with the binary.
    [[noreturn]] inline void Fatal(std::string_view msg) {
        std::println(std::cerr, "Crafter.Asset fatal: {}", msg);
        std::abort();
    }

    // One independently-decompressable GDeflate stream inside CompressedBlob::bytes.
    // Layout matches what VK_EXT_memory_decompression's VkDecompressMemoryRegionEXT
    // expects, minus the device addresses (which the consumer fills in).
    struct RegionMeta {
        std::uint64_t srcOffset;
        std::uint64_t compressedSize;
        std::uint64_t decompressedSize;
    };

    struct CompressedBlob {
        std::vector<std::byte> bytes;
        std::vector<RegionMeta> regions;

        std::uint64_t TotalDecompressedSize() const noexcept {
            std::uint64_t sum = 0;
            for (const RegionMeta& r : regions) sum += r.decompressedSize;
            return sum;
        }
    };

    // Compresses each input span as its own GDeflate tile-stream; concatenates
    // them into one byte buffer with a parallel region table. Streams are
    // independent and can be addressed individually by VkDecompressMemoryRegionEXT
    // entries on the GPU path.
    CompressedBlob CompressStreams(std::span<const std::span<const std::byte>> streams);

    // CPU fallback decoder. outputs.size() must equal blob.regions.size();
    // outputs[i].size() must equal blob.regions[i].decompressedSize.
    void DecompressCPU(const CompressedBlob& blob, std::span<const std::span<std::byte>> outputs);

    // Length-prefixed serialization of a CompressedBlob. Used by per-asset
    // SaveCompressed/LoadCompressed implementations after they've written
    // their own type-specific header.
    void WriteBlob(std::ostream& file, const CompressedBlob& blob);
    CompressedBlob ReadBlob(std::istream& file);
}