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trailview: fewer strewn rocks, and the ground carries them past the reach - #2932
This change fixes three problems with strewn rocks in TrailView: too many rocks, a hard edge where the rock instances end, and a wave of rocks that appears at that edge when the eye moves.
1. Fewer rocks, the same per square metre at every latitude
Rock points lie on a grid of 2^7 world units. A unit is shorter in metres towards the north, so on develop the rocks per square metre increase with latitude. Now each rock point stands for ROCK_POINT_M2 = 17 m² of ground. The keep chance uses the area of the point's own cell, at the cell's own latitude, so the threshold does not move when the eye moves.
Place
Cell
Develop
This change
Sheep's Head, 51.6° N
2.97 m, 8.79 m²
1
0.52
47° N
3.26 m, 10.62 m²
1
0.62
17 m² is 30 % fewer rocks than 12 m² (the first version of this pull request). It is near the prototype's 4 m spacing (16 m²). ROCK_POINT_M2 is one named constant in dressing/rocks.wgsl.
2. No edge where the instances end
Beyond the instance reach, the ground had no sign of rocks, so a field of rocks always ended in an edge. Now the ground paints the rocks:
dressing/rocks.wgsl holds the rock grid, the density (rock_density, from the rules: outcrops, material, lithology hardness, slope) and the hashes. rocks_of (the instances) and ground_colour (look.wgsl) both use it, so the rules stay in one place.
Each instance ends at its own distance between 55 % and 100 % of the reach (by its hash). The ground paints a rock's footprint (same point, size and turn) only past that distance, so each rock shows once, as an instance or as paint, and no ring shows.
The ground reads the instances' detail from the look uniform (screen.w), written in the same frame as the instance params. When a full pool pulls the instances nearer, the paint follows.
The ground samples a footprint at the pixel's middle, as the GPU rasterises an instance. So a far field of rocks stays a speckle. Pixels 8 to 16 m wide fade to the mean cover, times the share of instances that have ended there.
The painted colour is the rock's lit top, and from a low view its flank in its own light (backlit flanks are dark), so painted rocks match the instances from the ground and from above.
The reach is now 1000 m (develop: 300 m). I compared 400, 600 and 1000 m. At 400 and 600 m, a ground-level view up a hillside shows fewer 3D rocks in the upper part of the slope. At 1000 m the slope reads the same up to the ridge, and the extra cost is small (see below).
3. Review fixes
S1: rocks_of uses the tier's own distance and end: length(render_at(s, ground)) and ROCK_REACH_M * params.detail. A full pool or a large height difference now ends rocks where their tier ends, not before. The sun's view uses the same frame eye and detail, so the shadows match the rocks.
N1: the keep chance uses the point's latitude (rock_pick).
N2: a comment states where the keep chance saturates: a rules' share above ROCK_POINT_M2 / (12.5 m² × cos² latitude). With 17 m² that is only below about 27° N at the largest share.
N3: a rock less than half a pixel tall is skipped.
Second review round:
The paint follows detail (see above), per rock and for the mean cover.
A painted rock is clamped to its cell's side, not to 3 m. The cell side is computed once per row (3 cosh, not 9).
Small paint and instance mismatches at roads and material edges stay. They show only after the instance has ended.
Herds use the same hard cut at 1500 m. An animal there is smaller than one pixel, so this change does not touch herds.
The look stays data-driven: one generic implementation, and the density of the instances and of the painted ground comes only from the rules in data/trailview (outcrops, materials, lithology hardness).
Measurements
GPU renders of the Sheep's Head local release on a GTX 1660 SUPER, 2100 × 1290 px. "Rocks" is the rock instances that a frame stages.
View
Develop (300 m)
This change (1000 m)
main, eye A (heading=285.1, eye 1.6 m)
571
615
main, eye B (40 m forward)
391
458
slope, eye 30 m, A (heading=200)
750
2753
slope, eye 30 m, B (40 m forward)
827
2641
valley, eye 1.6 m, A (heading=180, up the hillside)
469
2399
valley, eye 1.6 m, B (40 m nearer)
351
2175
far slope, eye 120 m
598
3220
far ridge, eye 120 m
412
3374
tip, eye 30 m (all rocks within 300 m)
1364
865
The tip view has its rocks within 300 m, so it shows mostly the density cut (−37 %). The other views gain rocks from the longer reach.
In the develop renders, the rocks on the hillside stop at a line (the 300 m reach). In the new renders, the rocks continue to the ridge, from both eye positions of each pair, and no line or band shows where the instances end.
GPU time, median of 100 frames while the view turns (single run each; the terrain pass varies by about ±0.3 ms between runs):
View
Develop
400 m
600 m
1000 m
main: vegetation / terrain ms
0.68 / 2.30
0.70 / 2.61
0.71 / 2.59
0.76 / 3.09
slope: vegetation / terrain ms
0.63 / 2.46
0.59 / 2.77
0.62 / 2.78
0.67 / 2.64
valley: vegetation / terrain ms
0.72 / 1.83
0.77 / 2.30
0.79 / 2.29
0.79 / 2.09
far ridge: vegetation / terrain ms
0.55 / 2.63
0.51 / 3.16
0.56 / 3.08
0.59 / 2.91
rocks (main / slope / valley / far ridge)
572 / 749 / 466 / 412
317 / 507 / 323 / 426
394 / 1337 / 983 / 1403
624 / 2753 / 2405 / 3373
rock threads per frame
42 400
75 100
166 500
459 700
The vegetation pass holds all producers, the rocks included: 1000 m costs up to 0.08 ms more than develop. The painted rocks cost about 0.3 to 0.5 ms in the terrain pass at every reach.
With the eye 800 m above rocky ground (every ground pixel runs the paint loop), the terrain pass is 2.38 ms on develop and 2.37 ms with this change: no cost above the noise.
With detail forced to 0.7 in a scratch build (not committed), the valley pair and the far slope show no ring and no gap. Grazing views (eye 1.6 m, rocky slopes 500 to 1000 m away) are the same before and after the second round to within 0.06 of luma per band of 43 rows: the mean cover was not reached there, and the fix removes it by construction.
The terrain pass includes the instance draws and the painted rocks. The instance pool holds 131 072; these frames stage at most about 5 200, with no drops.
Checks
npm run check:wgsl: pass
npm run check (svelte-check): 0 errors, 0 warnings
npx vitest run src/lib/trailview: 39 files, 128 tests pass
npm run test:trailview -- --grep-invert @gpu: 2 pass
Not run: the @gpu browser tests, other suites. The renders and times are from the commits before each merge of develop (the merges touch no rock code).
Public docs did not change. The TrailView README names rocks.wgsl.
A rock point now stands for 12 m² of ground at every latitude, so rocks
per square metre no longer grow towards the north: about 27 % fewer at
Sheep's Head. The rock reach grows from 300 m to 400 m, and each rock
grows from nothing at the reach over 50 to 100 m by its hash, so no
line of rocks appears or vanishes as the eye moves.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
TrailView now uses shared helpers to calculate rock density and placement. The dressing shader uses those helpers for rock instances, and the ground shader blends painted rocks into ground shading beyond the instance handoff distance.
Changes: TrailView Rock Rendering
Layer / File(s)
Summary
Rock density and point helpers builder/web/src/lib/trailview/instances/hash.wgsl, builder/web/src/lib/trailview/dressing/rocks.wgsl
Adds shared hash utilities and rock helpers for terrain density, point selection, and instance properties.
Rock instance generation builder/web/src/lib/trailview/dressing/dressing.ts, builder/web/src/lib/trailview/dressing/dressing.wgsl, builder/web/src/lib/trailview/instances/emit.wgsl, builder/web/src/lib/trailview/README.md
The dressing shader uses shared helpers to select and cull rock instances. Dressing configuration updates rock reach and tier settings. The README describes the rock density, placement, and ground painting.
Painted rocks in ground shading builder/web/src/lib/trailview/dressing/rocks.wgsl, builder/web/src/lib/trailview/ground/look.wgsl
The ground shader computes painted rock coverage beyond the instance handoff distance and blends rock albedo into ground color.
sequenceDiagram
participant ground_colour
participant rocks_painted
participant rock_seen
ground_colour->>rocks_painted: Pass terrain, distance, and pixel footprint
rocks_painted-->>ground_colour: Return painted rock coverage
ground_colour->>rock_seen: Request rock albedo and lighting
rock_seen-->>ground_colour: Return shaded rock color
ground_colour->>ground_colour: Blend ground albedo with painted rocks
Loading
Possibly related issues
timohueser/OpenBikeComputer#2863: The issue describes a TrailView optimization wave, and this PR changes how rocks are rendered as instances and painted ground detail.
Possibly related PRs
timohueser/OpenBikeComputer#2887: The rock-density implementation consumes ground material, lithology, and region data described in this PR.
Suggested reviewers:claude
Merge Risk: Moderate · previous review 486d8
Crowded views can still show rocks disappearing before their painted footprints appear. Align the handoff before merging.
Pre-merge checks: 5
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The title accurately summarizes the main changes: reduced strewn rocks and ground-painted rock footprints beyond the instance reach. It is concise and specific.
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The rock grid, density and hashes move to dressing/rocks.wgsl, which the
instances and the ground colour share. Past 55 % of the reach the ground
paints each rock's footprint under it, and each instance ends at its own
distance, so a field of rocks has no edge where the instances end. The
reach grows to 1000 m.
A rock point stands for 17 m² at its own latitude (30 % fewer than
12 m²). rocks_of ends rocks at the tier's own distance and end, so a
full pool or a height difference no longer cuts grown rocks, and it
skips rocks under half a pixel. The producer hashes move to
instances/hash.wgsl so that the ground can include them.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
…ocks-fade
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
timohueser
changed the title
trailview: fewer strewn rocks, and rocks grow in at the reach
trailview: fewer strewn rocks, and the ground carries them past the reach
Oct 28, 2026
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Actionable comments posted: 1
🪄 Fix comments: Fix CodeRabbit comments on this PR
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Inline comments:
Review comments at @builder/web/src/lib/trailview/dressing/rocks.wgsl:
- Around line 96-97: Update the painted-coverage guard using ROCK_HANDOFF and
ROCK_REACH_M so coverage can begin by the effective end of rocks produced by
rocks_of when params.detail is reduced; preserve the density check and ensure no
gap remains between instance endings and painted coverage.
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The ground reads the instances' detail from the look uniform, set in the
same frame as the instance params. It paints a rock only past its own
instance end, and the mean cover only for the share of instances that
have ended, so no rock shows twice and a full pool leaves no ring. A
painted rock is clamped to its cell's side, and the cell side is
computed once per row.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Two adversarial review rounds are done. All findings are fixed in 2bdac2b (head 3f2e68c), and CI is green.
The one open CodeRabbit thread (rocks.wgsl, "Start painted coverage when instances can end") is already fixed in 2bdac2b. The instances' detail reaches the ground shader in look.screen.w, the paint starts at (1 − H)·R·detail, and each rock is painted only once far > rock_end(R·detail, h). It was verified with detail forced to 0.7: no ring and no gap. Resolve the thread, then merge.
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timohueser
changed the title
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Summary
This change fixes three problems with strewn rocks in TrailView: too many rocks, a hard edge where the rock instances end, and a wave of rocks that appears at that edge when the eye moves.
1. Fewer rocks, the same per square metre at every latitude
Rock points lie on a grid of 2^7 world units. A unit is shorter in metres towards the north, so on develop the rocks per square metre increase with latitude. Now each rock point stands for
ROCK_POINT_M2= 17 m² of ground. The keep chance uses the area of the point's own cell, at the cell's own latitude, so the threshold does not move when the eye moves.17 m² is 30 % fewer rocks than 12 m² (the first version of this pull request). It is near the prototype's 4 m spacing (16 m²).
ROCK_POINT_M2is one named constant indressing/rocks.wgsl.2. No edge where the instances end
Beyond the instance reach, the ground had no sign of rocks, so a field of rocks always ended in an edge. Now the ground paints the rocks:
dressing/rocks.wgslholds the rock grid, the density (rock_density, from the rules: outcrops, material, lithology hardness, slope) and the hashes.rocks_of(the instances) andground_colour(look.wgsl) both use it, so the rules stay in one place.detailfrom the look uniform (screen.w), written in the same frame as the instance params. When a full pool pulls the instances nearer, the paint follows.The reach is now 1000 m (develop: 300 m). I compared 400, 600 and 1000 m. At 400 and 600 m, a ground-level view up a hillside shows fewer 3D rocks in the upper part of the slope. At 1000 m the slope reads the same up to the ridge, and the extra cost is small (see below).
3. Review fixes
rocks_ofuses the tier's own distance and end:length(render_at(s, ground))andROCK_REACH_M * params.detail. A full pool or a large height difference now ends rocks where their tier ends, not before. The sun's view uses the same frame eye and detail, so the shadows match the rocks.rock_pick).ROCK_POINT_M2 / (12.5 m² × cos² latitude). With 17 m² that is only below about 27° N at the largest share.Second review round:
detail(see above), per rock and for the mean cover.cosh, not 9).Herds use the same hard cut at 1500 m. An animal there is smaller than one pixel, so this change does not touch herds.
The look stays data-driven: one generic implementation, and the density of the instances and of the painted ground comes only from the rules in
data/trailview(outcrops, materials, lithology hardness).Measurements
GPU renders of the Sheep's Head local release on a GTX 1660 SUPER, 2100 × 1290 px. "Rocks" is the rock instances that a frame stages.
heading=285.1, eye 1.6 m)heading=200)heading=180, up the hillside)The tip view has its rocks within 300 m, so it shows mostly the density cut (−37 %). The other views gain rocks from the longer reach.
In the develop renders, the rocks on the hillside stop at a line (the 300 m reach). In the new renders, the rocks continue to the ridge, from both eye positions of each pair, and no line or band shows where the instances end.
GPU time, median of 100 frames while the view turns (single run each; the terrain pass varies by about ±0.3 ms between runs):
The vegetation pass holds all producers, the rocks included: 1000 m costs up to 0.08 ms more than develop. The painted rocks cost about 0.3 to 0.5 ms in the terrain pass at every reach.
With the eye 800 m above rocky ground (every ground pixel runs the paint loop), the terrain pass is 2.38 ms on develop and 2.37 ms with this change: no cost above the noise.
With
detailforced to 0.7 in a scratch build (not committed), the valley pair and the far slope show no ring and no gap. Grazing views (eye 1.6 m, rocky slopes 500 to 1000 m away) are the same before and after the second round to within 0.06 of luma per band of 43 rows: the mean cover was not reached there, and the fix removes it by construction.The terrain pass includes the instance draws and the painted rocks. The instance pool holds 131 072; these frames stage at most about 5 200, with no drops.
Checks
npm run check:wgsl: passnpm run check(svelte-check): 0 errors, 0 warningsnpx vitest run src/lib/trailview: 39 files, 128 tests passnpm run test:trailview -- --grep-invert @gpu: 2 pass@gpubrowser tests, other suites. The renders and times are from the commits before each merge of develop (the merges touch no rock code).Public docs did not change. The TrailView README names
rocks.wgsl.Requirements: none
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