# Ambient traffic LOD detail-slot mapping · r460 ## What the executable proves The installed `SPEED2.EXE` part builder at `0x00634800` fills the traffic renderer's 63 records at owner `+0x17a8`. For each category and name bank it requests a base key with suffix `_B` (`0x00634943..0x00634980`), then adds `'A' + detailIndex` for detail indices 0 through 3 (`0x006349fd..0x00634a40`). Thus the four requested detail resources are suffixes `_A`, `_B`, `_C`, and `_D`, in that table order. The resolved handle is stored at `+0x17a8 + category*0x20 + bank*0x10 + detailIndex*4` (`0x00634a5a..0x00634a84`). When a higher detail resource is absent, the builder copies the prior detail handle; if detail A is absent, the slot stays null (`0x00634a8a..0x00634abd`). The draw pass at `0x006162e0` reads one of these four slots for each group. The traffic geometry export preserves the named `BODY_A`, `BODY_B`, and `BODY_C` meshes for each model. The installed geometry inventory has all three for 13 of 15 traffic definitions; BUS and FIRETRUCK have A/B. In all 15 definitions, the A mesh has the highest triangle count, B is next, and C is lowest where present. For example, TAXI has 496/323/222 triangles and COUPE has 526/344/229. This agrees with A/B/C being a descending detail series, but the names and triangle counts alone do not prove which body key the render-owner descriptor uses for each part category. ## What remained unresolved at r460 The renderer's size thresholds (40/20/10) are recovered, but the submitted level before threshold adjustment, the exact comparison direction, and the body-category key produced from the traffic descriptor are not yet joined to the installed `BODY_A/B/C` names. The model loader's two four-handle banks can also select different resources. Therefore the WebGL viewer remains on its upright BODY_A preview rather than switching suffixes at guessed distances. The per-variant signed axes are exported, so a future confirmed mapping can switch models without reusing the wrong body frame. ## Reproduction evidence The disassembly was read from the checked-in installed executable `reverse-engineering/source/pc-install/SPEED2.EXE` with the PE image base shown by `objdump -h` (`.text` at `0x00401000`). Relevant ranges: ```text 0x00634943..0x00634980 form the `_B` bank key 0x006349fd..0x00634a40 form `_A` through `_D` detail keys 0x00634a5a..0x00634a84 store the resolved detail handle 0x00634a8a..0x00634abd copy previous detail when a later slot is missing 0x006162e0 draw one selected handle from each four-level group ``` Model counts come from `traffic-ambient-models.json`, derived from each installed type-2 `GEOMETRY.BIN`. No viewer variant or distance behavior was changed in this audit. ## Follow-up: selector direction and installed bundle confirmation · r461 The comparison direction is now resolved from the instructions at `0x00616707..0x00616756`. Starting from the caller's level, the renderer increments the level while the computed metric is **below** the current threshold; it stops when the metric reaches that threshold and clamps the result to 0–3. The threshold table at `0x007a66ec` is `[40, 20, 10, 0]`. Thus near objects retain the incoming level and more distant objects advance to later detail slots. The caller at `0x006318b2..0x006318e5` passes globals `0x008a1c10` and `0x008a1c14` as the starting levels for the two banks. The setup code can set these to 0 or 1 based on a display configuration value, so the initial level is not a universal constant. The exact installed XP traffic bundles were recovered offline from `/home/jhylands/vms/winxp/winxp.qcow2`. I exposed the image read-only through `qemu-img convert` and `ntfs-3g` tools; the VM itself was not booted. All 15 type-2 `GEOMETRY.BIN` files are temporarily extracted under `/tmp/nfsu2-traffic/CARS/`. Their authored body names directly carry the suffixes `BODY_A`, `BODY_B`, and `BODY_C` (BUS and FIRETRUCK have A/B only); their exported triangle counts descend in that same order. The loader's missing `_D` fallback therefore has an available lower-detail source mesh to reuse for every type-2 traffic model. This confirms the selector's direction and the installed suffix inventory, but it does not yet prove how the loader's composed resource key joins a selected bank/detail slot to an authored body object. The initial level and the render context's size units also need to be mapped to the viewer's normalized scene units before a distance switch can claim retail behavior. Normal WebGL traffic remains on the measured BODY_A until those last joins are resolved. The screenshot and loader observation for that build are in the scrollable [r461 review entry](../webgl-city/review/#r461-current-drive-ready). ## Follow-up: direct geometry-hash join and WebGL LOD · r462 The missing suffix-to-object join is now established from the installed XP geometry bundles. Each `GEOMETRY.BIN` contains a type `0x00134003` table of resource name hashes. For all fifteen type-2 bundles, those hashes include the executable's 33-based name hash of every authored `*_BODY_A/B/C` object; the only exceptions are BUS and FIRETRUCK, which contain A/B. For TAXI, for example, `TAXI_BODY_A/B/C` hash to `0x3240e7a2`, `0x3240e7a3`, and `0x3240e7a4`, and all three values occur in its installed geometry table. The name-hash check passed for every available body variant across the 15 models. Together with the loader's ordered `_A`–`_D` requests, this maps detail slots 0/1/2 to BODY_A/B/C. Slot 3 reuses C, or B for the two models without C, because the loader copies the previous handle when a later detail is missing. The viewer now streams B/C after BODY_A makes traffic available and applies the recovered 40/20/10 thresholds. It computes a viewer-side bounded-size proxy from each BODY_A GLB's bounds and the camera-to-car distance; that keeps the threshold order and bounds-based shape measure, but the retail context's axis weights and scale units have not been recovered in the WebGL coordinate frame. The viewer defaults its initial level to 0 (highest detail). Debug mode reports the selected detail level and metric. Lower-detail meshes use their own exported axes and wheel anchors. The direct name-hash evidence resolves the body suffix map. The remaining fidelity limitation is the metric's exact retail context scaling, so this selector should be treated as source-ordered LOD with an approximate viewer distance metric rather than a bit-for-bit retail distance match. ## Follow-up: recover the executable's size equation · r463 The traffic draw wrapper at `0x006162e0` calls the oriented-bounds helper at `0x0048acb0` with a 3-unit near value and rejects objects whose returned size is below 4. The helper computes a weighted camera-to-object distance using the render transform's position and per-axis values, then compares `(distance - 3)` with `3 * 0.75`. It returns twice the object's render radius when distance is at most 5.25; otherwise it returns `floor(radius * 3 / (distance - 3))`. In the usual draw-state branch, the wrapper additionally scales this integer by the float at `0x007a6700` (`0.7`) and converts it back to an integer before the `< 4` cull. An alternate branch skips that scale based on two render-state values. The draw code then feeds the resulting bounded size into its 40/20/10 detail thresholds. The viewer now uses the helper's 3-unit piecewise equation and measures from each vehicle's transform origin. It still substitutes ordinary Euclidean distance for the helper's weighted transform distance and the BODY_A bounds sphere for the live render radius at object `+0x0c`; the exact retail instance radius, axis weights, and active wrapper branch are not exported in the current traffic manifest. The selected levels and switch distances therefore remain approximate. The viewer debug state reports its selected detail level and proxy metric. The packaged build loaded all 36 A/B/C body assets for the 12 traffic models enabled by its density quotas, with no failed requests or console errors. Six visible traffic cars were upright and road-supported in that capture. Their level selection is useful as a runtime check, but its exact distance equivalence remains open until the `+0x0c` retail radius and weighted axis values are recovered. Earlier wording in this note used a 4-unit near value; the wrapper disassembly passes `3.0` (`0x40400000`) at `0x006162f7`, so the equation above supersedes that reading. ## Reproduction evidence ```text objdump -D -Mintel --start-address=0x6162e0 --stop-address=0x616350 SPEED2.EXE objdump -D -Mintel --start-address=0x48acb0 --stop-address=0x48ad44 SPEED2.EXE objdump -D -Mintel --start-address=0x616707 --stop-address=0x616756 SPEED2.EXE ``` The first range shows the call and near-size cull, the second contains the radius-over-distance calculation, and the third applies the recovered `[40, 20, 10, 0]` detail thresholds.