feat: LOD 网格分级——meshopt 解析期简化 + 按距离/级联选级
vendored meshoptimizer 1.2（submodule 环境故障改直接 vendor）。Mesh 多 LOD：各级索引连续拼进同一 index buffer（共享顶点，LodRange 区间 选择），解析期 meshopt_simplify 生成链（LOD0=原始，每级目标减半， 相对误差 1e-2，小网格复用上级）；都在 worker 线程，加载零额外卡顿。 SceneRenderer 按 (mesh, LOD) 聚合 batch（lookup key = 指针<<8|lod）： 主视图按屏占比近似 radius/dist 选级（阈值 10/20 倍半径）；阴影级联 按级联序降级（越远越简）。Draw 按 batch.lod 选索引区间。 A/B 对比（100 背包 10×10，RTX 5060 Laptop，vsync off）： - 纯背包：LOD 开 93-95 fps / 关 90-107 fps —— 无显著差异 - 加 SunTemple：LOD 开 52-56 / 关 51-55 —— 无显著差异 结论：当前场景瓶颈不在顶点数（5060 顶点吞吐富余），LOD 基础设施 保留（几何复杂资产/低端 GPU/更大场景生效），帧率问题转向 Tracy GPU 时间线定位真实瓶颈。 坑：LodRange 记录"LOD 不足复用最后一级"时 first 不得继续累加 （buffer 无重复数据，累加必越界——VUID-08798 抓的）。
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#include "../src/meshoptimizer.h"
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#include <stdint.h>
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#include <stdlib.h>
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#include <string.h>
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void fuzzDecoder(const uint8_t* data, size_t size, size_t stride, int (*decode)(void*, size_t, size_t, const unsigned char*, size_t))
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{
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size_t count = 66; // must be divisible by 3 for decodeIndexBuffer; should be >=64 to cover large vertex blocks
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void* destination = malloc(count * stride);
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assert(destination);
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int rc = decode(destination, count, stride, reinterpret_cast<const unsigned char*>(data), size);
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(void)rc;
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free(destination);
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}
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void fuzzRoundtrip(const uint8_t* data, size_t size, size_t stride, int level)
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{
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size_t count = size / stride;
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size_t bound = meshopt_encodeVertexBufferBound(count, stride);
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void* encoded = malloc(bound);
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void* decoded = malloc(count * stride);
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assert(encoded && decoded);
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size_t res = meshopt_encodeVertexBufferLevel(static_cast<unsigned char*>(encoded), bound, data, count, stride, level, -1);
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assert(res > 0 && res <= bound);
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// encode again at the boundary to check for memory safety
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// this should produce the same output because encoder is deterministic
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size_t rese = meshopt_encodeVertexBufferLevel(static_cast<unsigned char*>(encoded) + bound - res, res, data, count, stride, level, -1);
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assert(rese == res);
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int rc = meshopt_decodeVertexBuffer(decoded, count, stride, static_cast<unsigned char*>(encoded) + bound - res, res);
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assert(rc == 0);
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assert(memcmp(data, decoded, count * stride) == 0);
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free(decoded);
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free(encoded);
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}
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size_t align(size_t value, size_t alignment)
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{
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return (value + alignment - 1) & ~(alignment - 1);
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}
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void fuzzDecodeMeshlet(size_t vertex_count, size_t triangle_count, const unsigned char* data, size_t size)
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{
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// raw decoding: allowed to write align(count, 4) elements
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unsigned int rt[256];
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unsigned int rv[256];
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meshopt_decodeMeshletRaw(rv + 256 - align(vertex_count, 4), vertex_count, rt + 256 - align(triangle_count, 4), triangle_count, data, size);
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// regular decoding: allowed to write align(count * size, 4) bytes
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// with variations for 3-byte triangles and 2-byte vertex references
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unsigned short rsv[256];
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unsigned char rbt[256 * 3];
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meshopt_decodeMeshlet(rv + 256 - vertex_count, vertex_count, 4, rt + 256 - triangle_count, triangle_count, 4, data, size);
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meshopt_decodeMeshlet(rsv + 256 - align(vertex_count, 2), vertex_count, 2, rt + 256 - triangle_count, triangle_count, 4, data, size);
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meshopt_decodeMeshlet(rv + 256 - vertex_count, vertex_count, 4, rbt + 256 * 3 - align(triangle_count * 3, 4), triangle_count, 3, data, size);
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meshopt_decodeMeshlet(rsv + 256 - align(vertex_count, 2), vertex_count, 2, rbt + 256 * 3 - align(triangle_count * 3, 4), triangle_count, 3, data, size);
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}
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void fuzzRoundtripMeshlet(const uint8_t* data, size_t size)
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{
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size_t triangle_count = size / 3;
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if (triangle_count > 256)
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triangle_count = 256;
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unsigned char buf[4096];
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size_t enc = meshopt_encodeMeshlet(buf, sizeof(buf), NULL, 0, reinterpret_cast<const unsigned char*>(data), triangle_count);
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assert(enc > 0);
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assert(enc <= meshopt_encodeMeshletBound(0, triangle_count));
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unsigned int rt4[256];
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int rc4 = meshopt_decodeMeshlet(static_cast<unsigned int*>(NULL), 0, rt4, triangle_count, buf, enc);
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assert(rc4 == 0);
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for (size_t i = 0; i < triangle_count; ++i)
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{
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unsigned char a = data[i * 3 + 0], b = data[i * 3 + 1], c = data[i * 3 + 2];
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unsigned int abc = (a << 0) | (b << 8) | (c << 16);
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unsigned int bca = (b << 0) | (c << 8) | (a << 16);
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unsigned int cba = (c << 0) | (a << 8) | (b << 16);
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unsigned int tri = rt4[i];
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assert(tri == abc || tri == bca || tri == cba);
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}
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unsigned char rt3[256 * 3];
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int rc3 = meshopt_decodeMeshlet(static_cast<unsigned int*>(NULL), 0, rt3, triangle_count, buf, enc);
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assert(rc3 == 0);
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for (size_t i = 0; i < triangle_count; ++i)
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{
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unsigned char a = data[i * 3 + 0], b = data[i * 3 + 1], c = data[i * 3 + 2];
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unsigned int abc = (a << 0) | (b << 8) | (c << 16);
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unsigned int bca = (b << 0) | (c << 8) | (a << 16);
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unsigned int cba = (c << 0) | (a << 8) | (b << 16);
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unsigned int tri = rt3[i * 3 + 0] | (rt3[i * 3 + 1] << 8) | (rt3[i * 3 + 2] << 16);
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assert(tri == abc || tri == bca || tri == cba);
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}
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}
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void fuzzRoundtripMeshletV(const uint8_t* data, size_t size)
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{
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size_t vertex_count = size / 4;
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if (vertex_count > 256)
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vertex_count = 256;
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unsigned char tri[4] = {0, 1, 2};
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unsigned char buf[4096];
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size_t enc = meshopt_encodeMeshlet(buf, sizeof(buf), reinterpret_cast<const uint32_t*>(data), vertex_count, tri, 1);
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assert(enc > 0);
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assert(enc <= meshopt_encodeMeshletBound(vertex_count, 1));
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unsigned int rv4[256];
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int rc4 = meshopt_decodeMeshlet(rv4, vertex_count, tri, 1, buf, enc);
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assert(rc4 == 0);
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for (size_t i = 0; i < vertex_count; ++i)
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assert(rv4[i] == reinterpret_cast<const uint32_t*>(data)[i]);
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unsigned short rv2[256];
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int rc2 = meshopt_decodeMeshlet(rv2, vertex_count, tri, 1, buf, enc);
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assert(rc2 == 0);
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for (size_t i = 0; i < vertex_count; ++i)
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assert(rv2[i] == uint16_t(reinterpret_cast<const uint32_t*>(data)[i]));
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}
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extern "C" int LLVMFuzzerTestOneInput(const uint8_t* data, size_t size)
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{
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// decodeIndexBuffer supports 2 and 4-byte indices
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fuzzDecoder(data, size, 2, meshopt_decodeIndexBuffer);
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fuzzDecoder(data, size, 4, meshopt_decodeIndexBuffer);
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// decodeIndexSequence supports 2 and 4-byte indices
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fuzzDecoder(data, size, 2, meshopt_decodeIndexSequence);
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fuzzDecoder(data, size, 4, meshopt_decodeIndexSequence);
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// decodeVertexBuffer supports any strides divisible by 4 in 4-256 interval
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// it's a waste of time to check all of them, so we'll just check a few with different alignment mod 16
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fuzzDecoder(data, size, 4, meshopt_decodeVertexBuffer);
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fuzzDecoder(data, size, 16, meshopt_decodeVertexBuffer);
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fuzzDecoder(data, size, 24, meshopt_decodeVertexBuffer);
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fuzzDecoder(data, size, 32, meshopt_decodeVertexBuffer);
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// encodeVertexBuffer/decodeVertexBuffer should roundtrip for any stride, check a few with different alignment mod 16
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// this also checks memory safety properties of the encoder
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// to conserve time, we only check one version/level combination, biased towards version 1
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uint8_t data0 = size > 0 ? data[0] : 0;
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int level = data0 % 5;
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meshopt_encodeVertexVersion(level < 4 ? 1 : 0);
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fuzzRoundtrip(data, size, 4, level);
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fuzzRoundtrip(data, size, 16, level);
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fuzzRoundtrip(data, size, 24, level);
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fuzzRoundtrip(data, size, 32, level);
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// validate that decodeMeshlet works on untrusted data and is memory safe within documented limits
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if (size > 2)
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fuzzDecodeMeshlet(data[0] + 1, data[1] + 1, reinterpret_cast<const unsigned char*>(data + 2), size - 2);
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// validate that index data roundtrips in meshlet encoding modulo rotation
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fuzzRoundtripMeshlet(data, size);
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// validate that vertex data roundtrips in meshlet encoding
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fuzzRoundtripMeshletV(data, size);
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return 0;
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}
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