From 44e5be8ce3c9b672edd78ff250b1e40ea87edd3d Mon Sep 17 00:00:00 2001 From: Mark Schlosser <47000437+markschlosseratbentley@users.noreply.github.com> Date: Fri, 17 Jul 2026 12:39:59 -0400 Subject: [PATCH 1/4] Clarify documentation for KHR_mesh_primitive_restart, add unit tests, and add a Sandcastle for visual verification of support. --- .../PrimitiveRestartLineStrip.glb | Bin 0 -> 11472 bytes .../primitive-restart-line-loop.glb | Bin 0 -> 2052 bytes .../primitive-restart-line-strip.glb | Bin 0 -> 2052 bytes .../primitive-restart-triangle-fan.glb | Bin 0 -> 2180 bytes .../primitive-restart-triangle-strip.glb | Bin 0 -> 2144 bytes .../MeshPrimitiveRestartKHR.gltf | 106 +++++++++++++++ packages/engine/Source/Scene/Model/Model.js | 6 +- packages/engine/Specs/Scene/GltfLoaderSpec.js | 43 ++++++ .../khr-mesh-primitive-restart-dev/index.html | 6 + .../khr-mesh-primitive-restart-dev/main.js | 126 ++++++++++++++++++ .../sandcastle.yaml | 5 + 11 files changed, 291 insertions(+), 1 deletion(-) create mode 100644 Apps/SampleData/models/PrimitiveRestart/PrimitiveRestartLineStrip.glb create mode 100644 Apps/SampleData/models/PrimitiveRestart/primitive-restart-line-loop.glb create mode 100644 Apps/SampleData/models/PrimitiveRestart/primitive-restart-line-strip.glb create mode 100644 Apps/SampleData/models/PrimitiveRestart/primitive-restart-triangle-fan.glb create mode 100644 Apps/SampleData/models/PrimitiveRestart/primitive-restart-triangle-strip.glb create mode 100644 Specs/Data/Models/glTF-2.0/MeshPrimitiveRestartKHR/glTF-Embedded/MeshPrimitiveRestartKHR.gltf create mode 100644 packages/sandcastle/gallery/khr-mesh-primitive-restart-dev/index.html create mode 100644 packages/sandcastle/gallery/khr-mesh-primitive-restart-dev/main.js create mode 100644 packages/sandcastle/gallery/khr-mesh-primitive-restart-dev/sandcastle.yaml diff --git a/Apps/SampleData/models/PrimitiveRestart/PrimitiveRestartLineStrip.glb b/Apps/SampleData/models/PrimitiveRestart/PrimitiveRestartLineStrip.glb 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  • - * {@link https://github.com/KhronosGroup/glTF/pull/2514|EXT_mesh_primitive_restart} + * {@link https://github.com/KhronosGroup/glTF/tree/main/extensions/2.0/Vendor/EXT_mesh_primitive_restart|EXT_mesh_primitive_restart} *
    • *
  • * {@link https://github.com/KhronosGroup/glTF/pull/2479|EXT_mesh_primitive_edge_visibility} @@ -105,6 +105,10 @@ import ModelImagery from "./ModelImagery.js"; * {@link https://github.com/KhronosGroup/glTF/tree/master/extensions/2.0/Khronos/KHR_materials_unlit/README.md|KHR_materials_unlit} *
    • *
  • + * {@link https://github.com/KhronosGroup/glTF/pull/2569|KHR_mesh_primitive_restart} + * (requires a WebGL 2 context; on WebGL 1, restart indices are not interpreted and affected primitives will render incorrectly) + *
    • + *
  • * {@link https://github.com/KhronosGroup/glTF/tree/main/extensions/2.0/Khronos/KHR_mesh_quantization|KHR_mesh_quantization} *
    • *
  • diff --git a/packages/engine/Specs/Scene/GltfLoaderSpec.js b/packages/engine/Specs/Scene/GltfLoaderSpec.js index eeb885ec12a6..9bb9e89c0a26 100644 --- a/packages/engine/Specs/Scene/GltfLoaderSpec.js +++ b/packages/engine/Specs/Scene/GltfLoaderSpec.js @@ -132,6 +132,8 @@ describe( "./Data/Models/glTF-2.0/StyledPoints/points-r5-g8-b14-y10.gltf"; const meshPrimitiveRestartTestData = "./Data/Models/glTF-2.0/MeshPrimitiveRestart/glTF/MeshPrimitiveRestart.gltf"; + const meshPrimitiveRestartKhrTestData = + "./Data/Models/glTF-2.0/MeshPrimitiveRestartKHR/glTF-Embedded/MeshPrimitiveRestartKHR.gltf"; const edgeVisibilityTestData = "./Data/Models/glTF-2.0/EdgeVisibility/glTF-Binary/EdgeVisibility.glb"; const edgeVisibilityMaterialTestData = @@ -4516,6 +4518,47 @@ describe( expect(loadedPrimitives.length).toBe(8); }); + it("loads model with KHR_mesh_primitive_restart extension", async function () { + const gltfLoader = await loadGltf(meshPrimitiveRestartKhrTestData, { + loadAttributesAsTypedArray: true, + }); + const components = gltfLoader.components; + const primitives = components.nodes[0].primitives; + + // Three line strips batched into a single LINE_STRIP primitive. + expect(primitives.length).toBe(1); + const primitive = primitives[0]; + expect(primitive.primitiveType).toBe(PrimitiveType.LINE_STRIP); + + // The inline 0xFFFF restart values must survive loading untouched. + const indices = primitive.indices; + expect(indices.count).toBe(9); + expect(indices.indexDatatype).toBe(IndexDatatype.UNSIGNED_SHORT); + expect(Array.from(indices.typedArray)).toEqual([ + 0, 1, 2, 0xffff, 3, 4, 0xffff, 5, 6, + ]); + }); + + it("loads model with KHR_mesh_primitive_restart extension and line styling", async function () { + const gltfLoader = await loadGltf(meshPrimitiveRestartKhrTestData); + const components = gltfLoader.components; + const primitive = components.nodes[0].primitives[0]; + + // Restart values reference no vertex, so they coexist with per-vertex + // line styling attributes such as CUMULATIVE_DISTANCE. + const cumulativeDistanceAttribute = getAttribute( + primitive.attributes, + VertexAttributeSemantic.CUMULATIVE_DISTANCE, + ); + expect(cumulativeDistanceAttribute).toBeDefined(); + expect(cumulativeDistanceAttribute.count).toBe(7); + + const material = primitive.material; + expect(material.lineStyle).toBeDefined(); + expect(material.lineStyle.width).toBe(3); + expect(material.lineStyle.pattern).toBe(61680); // 0xF0F0 + }); + it("loads model with EXT_mesh_primitive_edge_visibility extension", async function () { const gltfLoader = await loadGltf(edgeVisibilityTestData); const components = gltfLoader.components; diff --git a/packages/sandcastle/gallery/khr-mesh-primitive-restart-dev/index.html b/packages/sandcastle/gallery/khr-mesh-primitive-restart-dev/index.html new file mode 100644 index 000000000000..f30fef07b9d4 --- /dev/null +++ b/packages/sandcastle/gallery/khr-mesh-primitive-restart-dev/index.html @@ -0,0 +1,6 @@ + +
    +

    Loading...

    +
    diff --git a/packages/sandcastle/gallery/khr-mesh-primitive-restart-dev/main.js b/packages/sandcastle/gallery/khr-mesh-primitive-restart-dev/main.js new file mode 100644 index 000000000000..9d54ddcf22a2 --- /dev/null +++ b/packages/sandcastle/gallery/khr-mesh-primitive-restart-dev/main.js @@ -0,0 +1,126 @@ +import * as Cesium from "cesium"; +import Sandcastle from "Sandcastle"; + +// KHR_mesh_primitive_restart allows many line strips, line loops, triangle +// strips, or triangle fans to be batched into a single glTF primitive. The +// primitive's indices accessor may contain inline "restart" values (the +// maximum value for the accessor's component type (0xFF / 0xFFFF / +// 0xFFFFFFFF) to begin a new primitive. +// +// Requires WebGL 2 (PRIMITIVE_RESTART_FIXED_INDEX). Use the context dropdown +// to force a WebGL 1 context and observe lack of rendering support. +// +// The sample models below are from the KHR_mesh_primitive_restart proposal: +// https://github.com/KhronosGroup/glTF/pull/2569 +// Each contains a single mesh primitive with multiple topologies separated +// by inline restart values. + +let viewer; + +function createViewer(requestWebgl1) { + if (Cesium.defined(viewer)) { + viewer.destroy(); + } + viewer = new Cesium.Viewer("cesiumContainer", { + contextOptions: { requestWebgl1: requestWebgl1 }, + }); +} + +createViewer(false); + +const models = { + "Hilbert Curve (LINE_STRIP, 32-bit indices)": { + url: "../../SampleData/models/PrimitiveRestart/PrimitiveRestartLineStrip.glb", + heading: 0.0, + pitch: -45.0, + }, + "Line Strips": { + url: "../../SampleData/models/PrimitiveRestart/primitive-restart-line-strip.glb", + heading: -90.0, + pitch: 0.0, + }, + "Line Loops": { + url: "../../SampleData/models/PrimitiveRestart/primitive-restart-line-loop.glb", + heading: -90.0, + pitch: 0.0, + }, + "Triangle Strips": { + url: "../../SampleData/models/PrimitiveRestart/primitive-restart-triangle-strip.glb", + heading: -90.0, + pitch: 0.0, + }, + "Triangle Fans": { + url: "../../SampleData/models/PrimitiveRestart/primitive-restart-triangle-fan.glb", + heading: -90.0, + pitch: 0.0, + }, +}; + +const origin = Cesium.Cartesian3.fromDegrees(-75.152408, 39.946975, 50.0); +const modelMatrix = Cesium.Transforms.headingPitchRollToFixedFrame( + origin, + new Cesium.HeadingPitchRoll(0.0, 0.0, 0.0), +); + +let model; +let currentEntry; + +async function loadModel(entry) { + currentEntry = entry; + if (Cesium.defined(model)) { + viewer.scene.primitives.remove(model); + model = undefined; + } + + try { + model = viewer.scene.primitives.add( + await Cesium.Model.fromGltfAsync({ + url: entry.url, + modelMatrix: modelMatrix, + }), + ); + + model.readyEvent.addEventListener(() => { + const camera = viewer.camera; + const center = model.boundingSphere.center; + const r = 3.0 * Math.max(model.boundingSphere.radius, 1.0); + camera.lookAt( + center, + new Cesium.HeadingPitchRange( + Cesium.Math.toRadians(entry.heading), + Cesium.Math.toRadians(entry.pitch), + r, + ), + ); + camera.lookAtTransform(Cesium.Matrix4.IDENTITY); + }); + } catch (error) { + window.alert(`Error loading model: ${error}`); + } +} + +Sandcastle.addToolbarMenu( + Object.entries(models).map(([text, entry]) => ({ + text: text, + onselect: () => loadModel(entry), + })), +); + +Sandcastle.addToolbarMenu([ + { + text: "WebGL 2 (restart supported)", + onselect: () => { + createViewer(false); + loadModel(currentEntry); + }, + }, + { + text: "WebGL 1 (restart unsupported)", + onselect: () => { + createViewer(true); + loadModel(currentEntry); + }, + }, +]); + +await loadModel(Object.values(models)[0]); diff --git a/packages/sandcastle/gallery/khr-mesh-primitive-restart-dev/sandcastle.yaml b/packages/sandcastle/gallery/khr-mesh-primitive-restart-dev/sandcastle.yaml new file mode 100644 index 000000000000..3d13a277d65f --- /dev/null +++ b/packages/sandcastle/gallery/khr-mesh-primitive-restart-dev/sandcastle.yaml @@ -0,0 +1,5 @@ +title: KHR_mesh_primitive_restart - Dev +description: Load the KHR_mesh_primitive_restart sample models from the Khronos extension proposal (KhronosGroup/glTF#2569). Each model batches multiple line strips, line loops, triangle strips, or triangle fans into a single glTF primitive using inline restart index values. +labels: + - Development +development: true From 61be2bc3155067f85c571fe61b9e6c4fed211efd Mon Sep 17 00:00:00 2001 From: Mark Schlosser <47000437+markschlosseratbentley@users.noreply.github.com> Date: Fri, 17 Jul 2026 15:21:20 -0400 Subject: [PATCH 2/4] clarify undefined behavior of KHR_mesh_primitive_restart on webgl1 --- packages/engine/Source/Scene/Model/Model.js | 2 +- .../gallery/khr-mesh-primitive-restart-dev/main.js | 5 +++-- 2 files changed, 4 insertions(+), 3 deletions(-) diff --git a/packages/engine/Source/Scene/Model/Model.js b/packages/engine/Source/Scene/Model/Model.js index 52b4f70cf9c6..33b3dea6bd84 100644 --- a/packages/engine/Source/Scene/Model/Model.js +++ b/packages/engine/Source/Scene/Model/Model.js @@ -106,7 +106,7 @@ import ModelImagery from "./ModelImagery.js"; *
    • *
  • * {@link https://github.com/KhronosGroup/glTF/pull/2569|KHR_mesh_primitive_restart} - * (requires a WebGL 2 context; on WebGL 1, restart indices are not interpreted and affected primitives will render incorrectly) + * (requires a WebGL 2 context; behavior on WebGL 1 is undefined) *
    • *
  • * {@link https://github.com/KhronosGroup/glTF/tree/main/extensions/2.0/Khronos/KHR_mesh_quantization|KHR_mesh_quantization} diff --git a/packages/sandcastle/gallery/khr-mesh-primitive-restart-dev/main.js b/packages/sandcastle/gallery/khr-mesh-primitive-restart-dev/main.js index 9d54ddcf22a2..a50d3b144fd9 100644 --- a/packages/sandcastle/gallery/khr-mesh-primitive-restart-dev/main.js +++ b/packages/sandcastle/gallery/khr-mesh-primitive-restart-dev/main.js @@ -8,7 +8,8 @@ import Sandcastle from "Sandcastle"; // 0xFFFFFFFF) to begin a new primitive. // // Requires WebGL 2 (PRIMITIVE_RESTART_FIXED_INDEX). Use the context dropdown -// to force a WebGL 1 context and observe lack of rendering support. +// to force a WebGL 1 context, where results vary by browser/GPU backend: +// nothing, corrupted geometry, or even correct rendering. // // The sample models below are from the KHR_mesh_primitive_restart proposal: // https://github.com/KhronosGroup/glTF/pull/2569 @@ -115,7 +116,7 @@ Sandcastle.addToolbarMenu([ }, }, { - text: "WebGL 1 (restart unsupported)", + text: "WebGL 1 (restart unsupported; behavior varies)", onselect: () => { createViewer(true); loadModel(currentEntry); From cac5b8fd18917e95481dcf944d8067628a694611 Mon Sep 17 00:00:00 2001 From: Mark Schlosser <47000437+markschlosseratbentley@users.noreply.github.com> Date: Mon, 20 Jul 2026 07:36:31 -0400 Subject: [PATCH 3/4] KHR_mesh_primitive_restart CHANGES.md entry --- CHANGES.md | 1 + 1 file changed, 1 insertion(+) diff --git a/CHANGES.md b/CHANGES.md index 1de2345c26db..416ee7b31768 100644 --- a/CHANGES.md +++ b/CHANGES.md @@ -8,6 +8,7 @@ - Added `Texture.defaultColor` static property to allow customizing the default placeholder texture color. [#13597](https://github.com/CesiumGS/cesium/pull/13597) - Added support for draping clamped vector tile polylines onto terrain, with screen-space-constant line width and per-feature styling via `Cesium3DTileStyle`. [#13577](https://github.com/CesiumGS/cesium/pull/13577) +- Added support for the [`KHR_mesh_primitive_restart`](https://github.com/KhronosGroup/glTF/pull/2569) glTF extension. [#13634](https://github.com/CesiumGS/cesium/pull/13634) #### Fixes :wrench: From 283dc26d0369ddb6444414f98ea438504283fe01 Mon Sep 17 00:00:00 2001 From: Mark Schlosser <47000437+markschlosseratbentley@users.noreply.github.com> Date: Mon, 20 Jul 2026 08:20:08 -0400 Subject: [PATCH 4/4] KHR_mesh_primitive_restart model licensing --- Apps/SampleData/models/PrimitiveRestart/README.md | 9 +++++++++ LICENSE.md | 6 ++++++ 2 files changed, 15 insertions(+) create mode 100644 Apps/SampleData/models/PrimitiveRestart/README.md diff --git a/Apps/SampleData/models/PrimitiveRestart/README.md b/Apps/SampleData/models/PrimitiveRestart/README.md new file mode 100644 index 000000000000..008f0e3b0055 --- /dev/null +++ b/Apps/SampleData/models/PrimitiveRestart/README.md @@ -0,0 +1,9 @@ +# PrimitiveRestart + +Sample models demonstrating the [`KHR_mesh_primitive_restart`](https://github.com/KhronosGroup/glTF/pull/2569) glTF extension. Each model contains a single mesh primitive batching multiple topological primitives (line strips, line loops, triangle strips, or triangle fans) separated by inline restart index values. + +## License Information + +Created by Don McCurdy as test data for the `KHR_mesh_primitive_restart` extension proposal ([KhronosGroup/glTF#2569](https://github.com/KhronosGroup/glTF/pull/2569)). + +Licensed under [CC BY 4.0](https://creativecommons.org/licenses/by/4.0/). See also the `KHR_mesh_primitive_restart sample models` entry in [LICENSE.md](../../../../LICENSE.md). diff --git a/LICENSE.md b/LICENSE.md index abfcfb8b0bfe..8e426a08213c 100644 --- a/LICENSE.md +++ b/LICENSE.md @@ -1045,6 +1045,12 @@ Creative Commons Attribution 4.0 International (c) copyright 2019, Dr Edward Alan Lockhart https://sketchfab.com/3d-models/parc-lead-mine-4759a23abbff454c8c682ff9b02ba111 +### KHR_mesh_primitive_restart sample models + +Creative Commons Attribution 4.0 International +(c) copyright 2026, Don McCurdy +https://github.com/KhronosGroup/glTF/pull/2569 + ### GitHub logo https://github.com/logos