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ifcviewer: quantize VBO to 16 B/vertex (sidecar v6)

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Position now u16x3 normalized against each mesh's local AABB; normal
oct-encoded to i16x2; RGBA8 colour unchanged. Per-mesh dequant basis
lives in a new MeshGpu SSBO at binding 2; both main and pick shaders
mix() against it before applying the instance transform.

Drops VBO and sidecar size by ~43 % (28 -> 16 B/vert), which matters
mostly for warm-load downloads of precomputed sidecars and steady-state
VRAM. LodBuilder dequantizes positions into a scratch buffer before
calling meshopt, since meshoptimizer needs float positions.

Also fixes a streaming-time crash in cullAndUploadVisible: bvh_items
was only populated at finalize, but the linear fallback indexes it
during streaming. Mirror BvhItem appends in uploadInstanceChunk so the
hot path stays valid before the BVH is built.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
This commit is contained in:
Dion Moult
2026-04-14 21:54:15 +10:00
parent 09ffdd2028
commit 574bcfa6c5
9 changed files with 299 additions and 72 deletions
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src/ifcviewer/LodBuilder.cpp
+28 -8
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@@ -33,9 +33,8 @@ void buildLods(SidecarData& sd,
float target_error) {
if (sd.meshes.empty() || sd.vertices.empty() || sd.indices.empty()) return;
const size_t vtx_stride_bytes = INSTANCED_VERTEX_STRIDE_BYTES;
const size_t vtx_stride_floats = INSTANCED_VERTEX_STRIDE_FLOATS;
const size_t total_vertex_count = sd.vertices.size() / vtx_stride_floats;
const size_t vtx_stride_bytes = INSTANCED_VERTEX_STRIDE_BYTES;
const size_t total_vertex_count = sd.vertices.size() / vtx_stride_bytes;
// Env var knobs so we can tune without rebuilding.
// IFC_LOD_LOCK_BORDER=1 re-enable LockBorder (off by default: BIM
@@ -73,8 +72,10 @@ void buildLods(SidecarData& sd,
// Scratch buffers reused across meshes so we only allocate once.
std::vector<uint32_t> simplified;
std::vector<uint32_t> shadow;
std::vector<float> dequant_pos; // 3 floats/vertex, dequantized
simplified.reserve(1024);
shadow.reserve(1024);
dequant_pos.reserve(1024 * 3);
int dbg_printed = 0;
int dbg_rejected_savings = 0;
@@ -101,8 +102,27 @@ void buildLods(SidecarData& sd,
const uint32_t first_index = mesh.ebo_byte_offset / sizeof(uint32_t);
if (first_index + mesh.index_count > sd.indices.size()) continue;
const float* positions =
sd.vertices.data() + base_vertex * vtx_stride_floats;
// Dequantize positions for this mesh into a temp float array.
// meshopt needs contiguous float3 positions with a known stride;
// quantized bytes aren't directly usable.
const uint8_t* quant_base =
sd.vertices.data() + base_vertex * vtx_stride_bytes;
dequant_pos.resize(static_cast<size_t>(mesh.vertex_count) * 3);
const float extent[3] = {
mesh.local_aabb_max[0] - mesh.local_aabb_min[0],
mesh.local_aabb_max[1] - mesh.local_aabb_min[1],
mesh.local_aabb_max[2] - mesh.local_aabb_min[2],
};
for (uint32_t v = 0; v < mesh.vertex_count; ++v) {
const uint16_t* p = reinterpret_cast<const uint16_t*>(
quant_base + v * vtx_stride_bytes);
for (int a = 0; a < 3; ++a) {
float t = p[a] / 65535.0f;
dequant_pos[v * 3 + a] = mesh.local_aabb_min[a] + t * extent[a];
}
}
const float* positions = dequant_pos.data();
const size_t local_pos_stride = sizeof(float) * 3;
const uint32_t* indices = sd.indices.data() + first_index;
const size_t target_index_count = std::max<size_t>(
@@ -121,7 +141,7 @@ void buildLods(SidecarData& sd,
indices, mesh.index_count,
positions, mesh.vertex_count,
sizeof(float) * 3, // compare only xyz
vtx_stride_bytes);
local_pos_stride);
simplified.resize(mesh.index_count);
float result_error = 0.0f;
@@ -135,7 +155,7 @@ void buildLods(SidecarData& sd,
new_index_count = meshopt_simplifySloppy(
simplified.data(),
indices, mesh.index_count,
positions, mesh.vertex_count, vtx_stride_bytes,
positions, mesh.vertex_count, local_pos_stride,
target_index_count, target_error,
&result_error);
} else {
@@ -144,7 +164,7 @@ void buildLods(SidecarData& sd,
new_index_count = meshopt_simplify(
simplified.data(),
shadow.data(), mesh.index_count,
positions, mesh.vertex_count, vtx_stride_bytes,
positions, mesh.vertex_count, local_pos_stride,
target_index_count, target_error,
options, &result_error);
}