GPU deformation — v26

Read this before creating a deformable or sculptable GPU mesh. Refresh the Game
iframe after installing the v26 player; Run does not replace engine code. Check
getGPUCapabilities().gpuPlasticDeformation and gpuMeshSculpting.

Impact-driven plastic flow — experimental browser contact

The plastic rest-shape update works, but Chrome impact tests exposed excessive
sphere/sheet overlap (0.14–1.25 m in the tested 3.5–9 m drop range). One-sided
contact avoids an underside-normal flip but does not fix the overlap. Do not use
this spring-sheet contact as a blocking game surface yet. The saved Impact
Deformation draft is a diagnostic comparison, not an accepted game example.
Use the separately validated GPU beam for the diving-board experiment.

Create an editable GPU mesh, enable its linear-elastic mesh physics, then register
ordinary CS rigidbodies with addGPUCollider. Existing CS object mass, collider,
interpolation, constraints and physics scripts remain unchanged.

await createGPUMesh("sheet", "grid", {
    origin:{x:0,y:3,z:0}, size:{x:6,y:1,z:6}, resolution:12
});
await enableGPUMeshPhysics("sheet", {
    mass:.25, stiffness:100, damping:2, foundation:5,
    pinBoundary:true, pinnedVertices:[], contactSidedness:"oneSided",
    yieldStrain:.025, plasticCreep:5
});
await showGPUPhysicsStrain("sheet", .2);
load("sphere", "ball", 0, 5, 0);
await addGPUCollider("sheet", "ball");

yieldStrain and plasticCreep must both be positive. Leave both at zero for
elastic-only motion. Above the yield threshold, GPU neighbor-edge strain updates
the mesh's solver rest shape gradually; resetGPUPhysics restores the initial
shape. showGPUPhysicsStrain colors the mesh by maximum neighbor-edge strain. This
color is strain, not engineering stress in pascals.

This is a fixed-topology, spring-network membrane with bounded plastic rest-state
flow. It is useful for a small dentable sheet or panel demonstration. It is not
continuum plasticity, a general soft-body material, fracture, tearing, cuts,
fragment spawning, or dynamic topology. Keep meshes within the existing mesh
physics limit (4,096 vertices / 8,192 triangles). The solver owns its buffers;
do not run a custom WGSL program against a mesh while mesh physics owns it.

GPU surface sculpting

Make an editable GPU mesh, then add local soft brush strokes:

await createGPUMesh("surface", "grid", {
    origin:{x:0,y:0,z:0}, size:{x:8,y:1,z:8}, resolution:32
});
await sculptGPUMesh("surface", {x:0,y:0,z:0}, .55, {radius:2.3});
await sculptGPUMesh("surface", {x:2,y:0,z:0}, -.3, {
    radius:1.4, direction:{x:0,y:1,z:0}
});

center is a Unity-world point. amount is a signed distance: positive raises and
negative lowers along the normalized direction (default up). radius sets the
brush reach. Existing mesh mask weights limit each stroke. Strokes accumulate;
refreshGPUMeshNormals runs after each stroke. resetGPUMesh restores the mesh and
clears the brush offsets. Sculpting is rejected while GPU mesh physics owns the
mesh. The brush edits the GPU surface only: it does not change the source object,
terrain data, or PhysX collider. For collision, keep using the original collider
or design a separate collision proxy; don't claim the sculpted surface is a
matching physics boundary.

Examples

catalog/examples/gpu-deformation-impact.js — compare elastic and plastic impact,
inspect GPU contacts/strain and reset both the surface and the stock CS sphere.
catalog/examples/gpu-surface-sculpting.js — raise, carve, form a ridge, inspect
current bounds, and restore the original mesh.

Native verification (Unity 6.4, Metal)

The editor test dropped the stock sphere onto a pinned GPU grid, checked finite
displacement and that the sphere stayed above the sheet, removed the impact body,
and checked exact rest reset. Observed maximum rest-shape displacement was
0.07732074 m; minimum sphere Y was 2.950044 m; maximum sphere speed was
5.689798 m/s. A second check confirmed local sculpt falloff and exact reset. These
are synchronous native results; they did not predict the asynchronous Chrome
contact failure described above. The settings-patch regression also passes: an
omitted pin list and an empty pin list are equivalent; changing pin membership
still requires recreation.

Chrome/WebGPU, 2026-11-04: surface sculpting passed. An 8 m square, resolution-32
mesh measured Y=0..0.55 m after Raise hill, -0.45..0 after Carve basin, 0..0.38 m
after Build ridge, and exactly 0..0 after Reset. Normals and the visible surface
updated. These are geometry-only operations; the physics-boundary limitation
above remains. Evidence: beam-release-20261104/tests/browser.json.