WebGPU: measurement dimension lines use unsupported GLSL LineMaterial

[rihokirss]

Length measurement labels and endpoint markers appear in the WebGPU viewer, but the dimension lines are missing. The console reports:

THREE.NodeBuilder: Material "LineMaterial" is not compatible.

Versions

• @thatopen-platform/components-beta: 3.5.18
• @thatopen-platform/components-front-beta: 3.5.16
• @thatopen-platform/fragments-beta: 3.5.9
• three: 0.185.0
• Linux, Chromium, hardware WebGPU on AMD RDNA 3 (no WebGL fallback)

Reproduction

In an initialized beta world using the WebGPU PostproductionRenderer, create a stock LengthMeasurement and add a line within the camera view:

import * as THREE from "three/webgpu";
import * as OBCF from "@thatopen-platform/components-front-beta";

const measurement = components.get(OBCF.LengthMeasurement);
measurement.world = world;
measurement.list.add(new OBCF.Line(
  new THREE.Vector3(-2, -2, 0),
  new THREE.Vector3(2, 2, 2),
));
// Camera looking at the origin from approximately (8, 7, 10).

console.log(measurement.linesMaterial.type); // "LineMaterial"
console.log(measurement.linesMaterial.isShaderMaterial); // true

Expected: a visible colored dimension line joining the endpoints, alongside its label.

Actual: labels/endpoints render, but the line does not; the material compatibility warning appears. The equivalent measurement works in a WebGL viewer.

Source-level cause

The beta Measurement base class creates a NearPlaneLineMaterial, which extends the GLSL LineMaterial from three/examples/jsm/lines/LineMaterial.js. DimensionLine.createLine() also constructs the WebGL LineSegments2. The WebGPU path needs the node-material equivalents.

Locally verified workaround

In the WebGPU build only:

1. Replace the default measurement line material with Line2NodeMaterial, preserving the color and 2 px width, with depthTest: false and depthWrite: false.
2. Give this adapter material an isLineMaterial flag so the current DimensionLine factory creates segment geometry instead of a plain THREE.Line.
3. Replace the dimension's line object with three/examples/jsm/lines/webgpu/LineSegments2.js, reusing its LineSegmentsGeometry and material. Keep it under the same parent and update dimension.lineElement, so geometry updates, visibility, and disposal continue to work.

This restored the lines without modifying the beta packages. A guard leaves an upstream node material untouched when one becomes available.

Validation

• Reproduced using the stock beta LengthMeasurement class, independently of a custom measurement subclass.
• On the same hardware WebGPU backend, a 9×9 pixel region around a point one-quarter along the stock dimension had 0 blue pixels before and 21 after applying the adapter; the compatibility warning disappeared.
• Verified preview and committed lines in free and edge modes, plus a local orthogonal mode built on createLineElement(); checked resize, hide/show, and deletion.
• Verified both the minimal FXAA pipeline and enabled postproduction; no new browser rendering errors.
• The stable WebGL viewer's measurements still pass the same checks.

Could the beta measurement factory select the appropriate line material and line object for the renderer? The shared Measurement base suggests other measurement tools using its fat-line material may also need the same adaptation; those tools were not tested here.

[rihokirss]

A separate picker behavior also surfaced while checking the measurement cursor in this WebGPU beta (same versions as above): a valid surface hit can be returned while its CSS2D marker remains hidden or is never created.

With the default mixed snap classes [LINE, POINT, FACE], GraphicVertexPicker.get() only displays the marker for POINT/LINE results, or for a FACE result when FACE is the only enabled class. A FACE result in mixed mode falls through to the marker-hide path. This is separate from the GLSL line-material problem: the surface point is found correctly, but there is no visible point indicator.

Observed in the browser over model surfaces:

measurement.lastPick.snappingClass = 2 (FACE)
measurement._vertexPicker.marker = null

The stable picker displays a marker for these hits. A small local fallback restores the existing picker's marker for a fresh FACE result when the picker has left it hidden. It uses the normal FACE styling, does not change snapping results, and does nothing if the native picker already shows a marker. No additional raycast is needed.

Verified actual pointer movement over model surfaces, marker pixels and alignment with the picked world point, no-hit hiding, disabling the tool, leaving/re-entering the viewer, and the stable WebGL behavior. Measurement preview and line rendering retain their normal render path; the restored marker only needs a CSS2D repaint.