Load edge visibility accessors as typed arrays to cut JS heap use

[markschlosseratbentley]

Description

GltfLoader.loadEdgeVisibility loaded edge-visibility accessors (visibility, silhouetteNormals, lineStrings[].indices) via loadAccessor, converting binary data into plain JS number arrays retained for the tileset's lifetime. On edge-heavy tilesets this inflated JS heap ~12x (39.5 MB -> ~460 MB on a 306-tile test dataset).

• Load all three accessors with loadAccessorTypedArray instead
• EdgeVisibilityPipelineStage now reads silhouetteNormals as a flat packed Int8Array (was Cartesian3[])
• Specs updated for the new shape; added a value-level decode test for silhouette face normals

Measured heap delta after fix: ~460 MB -> 45 MB (Tafe_Sydney), 31.5 MB -> 6.6 MB (04_Plant). FPS/GPU memory unchanged.

Note: primitive.edgeVisibility.silhouetteNormals changes shape from Cartesian3[] to flat Int8Array (internal/undocumented API).

Explanation

Plain JS number arrays store elements as V8 tagged values or heap-allocated doubles rather than raw bytes, so 1-byte binary values inflate several-fold; a heap allocation profile attributed ~340 MB of the regression to loadAccessorValues. Typed arrays store the data as a compact binary buffer, 1 byte per element.

Issue number and link

#13640

Testing plan

• All EdgeVisibility unit specs pass (gulp test --webglStub), including new typed-array assertions and a value-level silhouette-normal decode test.
• Benchmarked with a Playwright harness (fresh browser per run, forced GC, empty-scene baseline delta): on a 306-tile edge-heavy tileset, JS heap delta dropped ~460 MB -> ~45 MB; FPS, GPU bytes, and triangle counts unchanged. Control runs on unpatched builds reproduced the original numbers.
• Manually verified silhouette edge rendering in Sandcastle.

Results of benchmarking using Playwright harness

Before these changes

---
config:
  themeVariables:
    xyChart:
      plotColorPalette: "#1f77b4, #ff7f0e, #2ca02c, #d62728, #9467bd"
---
xychart-beta
    title "JS heap delta (peak view), as a multiple of no-ext"
    x-axis ["A0", "A1", "B0", "B1", "C0", "C1", "D0", "D1", "E0", "E1"]
    y-axis "relative" 0 --> 22.0
    bar [1.0, 5.7, -1.0, -1.0, -1.0, -1.0, -1.0, -1.0, -1.0, -1.0]
    bar [-1.0, -1.0, 1.0, 6.5, -1.0, -1.0, -1.0, -1.0, -1.0, -1.0]
    bar [-1.0, -1.0, -1.0, -1.0, 1.0, 1.3, -1.0, -1.0, -1.0, -1.0]
    bar [-1.0, -1.0, -1.0, -1.0, -1.0, -1.0, 1.0, 19.2, -1.0, -1.0]
    bar [-1.0, -1.0, -1.0, -1.0, -1.0, -1.0, -1.0, -1.0, 1.0, 11.7]

Loading

Bar	Dataset	Variant	Value
A0	Dataset A	no-ext	5.5 MB
A1	Dataset A	edges	31.3 MB
B0	Dataset B	no-ext	20.3 MB
B1	Dataset B	edges	131.4 MB
C0	Dataset C	no-ext	13.5 MB
C1	Dataset C	edges	17.2 MB
D0	Dataset D	no-ext	13.8 MB
D1	Dataset D	edges	264.4 MB
E0	Dataset E	no-ext	37.5 MB
E1	Dataset E	edges	438.5 MB

After these changes

---
config:
  themeVariables:
    xyChart:
      plotColorPalette: "#1f77b4, #ff7f0e, #2ca02c, #d62728, #9467bd"
---
xychart-beta
    title "JS heap delta (peak view), as a multiple of no-ext"
    x-axis ["A0", "A1", "B0", "B1", "C0", "C1", "D0", "D1", "E0", "E1"]
    y-axis "relative" 0 --> 1.5
    bar [1.0, 1.1, -1.0, -1.0, -1.0, -1.0, -1.0, -1.0, -1.0, -1.0]
    bar [-1.0, -1.0, 1.0, 1.3, -1.0, -1.0, -1.0, -1.0, -1.0, -1.0]
    bar [-1.0, -1.0, -1.0, -1.0, 1.0, 1.2, -1.0, -1.0, -1.0, -1.0]
    bar [-1.0, -1.0, -1.0, -1.0, -1.0, -1.0, 1.0, 1.2, -1.0, -1.0]
    bar [-1.0, -1.0, -1.0, -1.0, -1.0, -1.0, -1.0, -1.0, 1.0, 1.2]

Loading

Bar	Dataset	Variant	Value
A0	Dataset A	no-ext	5.7 MB
A1	Dataset A	edges	6.4 MB
B0	Dataset B	no-ext	20.3 MB
B1	Dataset B	edges	25.8 MB
C0	Dataset C	no-ext	13.6 MB
C1	Dataset C	edges	17.0 MB
D0	Dataset D	no-ext	13.9 MB
D1	Dataset D	edges	16.2 MB
E0	Dataset E	no-ext	37.5 MB
E1	Dataset E	edges	44.8 MB

Author checklist

• I have submitted a Contributor License Agreement
• I have added my name to CONTRIBUTORS.md
• I have updated CHANGES.md with a short summary of my change
• I have added or updated unit tests to ensure consistent code coverage
• I have updated the inline documentation, and included code examples where relevant
• I have performed a self-review of my code

AI acknowledgment

• I used AI to generate content in this PR
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If yes, I used the following Tools(s) and/or Service(s):

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If yes, I used the following Model(s):

Claude Fable 5

[github-actions]

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