Viewing LOD Representation Selection

The viewing.lod module selects authored SceneModel representations on a per-view basis. It does not generate shell geometry or create SceneModel content. Shells, impostors and other LOD representations are authored in model.lod and stored in SceneRepSet metadata.

LOD suppression is separate from ordinary application visibility. Renderers combine both states while drawing:

effectiveVisible = applicationVisible && !lodSuppressed
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Use RepresentationLODSelector to discover representation sets whose selection metadata uses "projectedSize" and select one representation per view.

Representation selection is also the fast path for switching visibility of large object groups. Instead of rewriting ordinary object visibility for every object in a representation, the viewer records the selected representation per View and lets renderers suppress non-selected representation memberships at batch or draw-list granularity.

Runtime Shape

classDiagram
    direction TB
    class RepresentationLODSelector {
      +enabled
      +setEnabled(enabled)
      +updateView(view)
      +updateAllViews()
      +getActiveRepId(view, repSet)
      +clear()
      +destroy()
    }
    class LODVisibility {
      +isSuppressed(viewId, objectId)
      +setSuppressed(viewId, objectIds, suppressed)
      +setSelectedRep(viewId, selectionId, reps, selectedRepId)
      +getViewVersion(viewId)
    }
    RepresentationLODSelector ..> LODVisibility : suppresses non-selected reps

Basic Usage

The selector works with representation sets already present in loaded SceneModels. Those sets can be authored offline, generated with model.lod.createShellRep, or loaded from a format such as XGF that preserves representation metadata.

Create the selector after the Viewer exists:

import {RepresentationLODSelector} from "@xeokit/sdk/viewing/lod";

const selector = new RepresentationLODSelector({
  viewer
});
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The selector discovers eligible representation sets automatically. A set is eligible when its selection metadata uses the projected-size strategy:

sceneModel.createRepSet({
  id: "floor3",
  defaultRepId: "detailed",

  selection: {
    strategy: "projectedSize",
    hysteresisPixels: 16
  },

  reps: [
    {
      id: "detailed",
      objectIds: [
        "wall1",
        "wall2",
        "slab1"
      ],
      range: {
        minPixels: 160
      }
    },
    {
      id: "shell",
      objectIds: [
        "__floor3_shell"
      ],
      range: {
        maxPixels: 128
      }
    }
  ]
});
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After the set exists, camera and viewport changes update selection for each View. Applications normally do not need to call updateView() manually.

Loading a Model With Representations

For a model format that restores SceneModel representation sets, create the selector once and load the model normally:

const selector = new RepresentationLODSelector({viewer});

const sceneModel = scene.createModel({
  id: "hospital"
}).value;

await xgfLoader.load({
  fileData,
  sceneModel
});

// Newly loaded representation sets are discovered automatically.
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Inspecting Selection

Use getActiveRepId() when UI or diagnostics need to show what a View is currently using:

const repSet = sceneModel.repSets["floor3"];
const activeRepId = selector.getActiveRepId(view, repSet);
const mode = selector.getMode(view, repSet);

console.log(activeRepId, mode);
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getMode() returns:

• "default" when the set's default representation is selected,
• "selected" when another representation is selected,
• "invalid" when the set cannot currently be evaluated.

Enable, Disable and Destroy

Disabling the selector clears only selector-owned representation suppression. It does not change ordinary object visibility:

selector.setEnabled(false); // all representations are unsuppressed again
selector.setEnabled(true);  // selection resumes

selector.destroy();         // clears suppression and removes event handlers
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Multiple Views

Selection state is per View. Two Views can show different representations of the same SceneModel at the same time:

const nearView = viewer.viewList[0];
const farView = viewer.viewList[1];
const repSet = sceneModel.repSets["floor3"];

selector.updateView(nearView);
selector.updateView(farView);

console.log(selector.getActiveRepId(nearView, repSet)); // "detailed"
console.log(selector.getActiveRepId(farView, repSet));  // "shell"
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