SelectionOutline

SelectionOutline in @luma.gl/anari draws a WebGPU selection overlay from a sampled r32uint visible-placement ID texture. It borrows the texture and draws an inward stroke only on pixels matching the selected identifier. Background and other visible objects stay unchanged, including objects occluding the selected placement.

import {SelectionOutline} from '@luma.gl/anari';

const outline = new SelectionOutline(graphicsDevice);
// Render and submit the scene before capturing its current primary-hit channels.
frame.render();
graphicsDevice.submit();
const channels = frame.captureChannels();
if (channels) {
  try {
    const selectedIdentifier = channels.identifiers.findIndex(
      identity => identity.placementId === selectedPlacementId
    ) + 1;
    const renderPass = graphicsDevice.beginRenderPass({
      clearColor: false,
      clearDepth: false,
      clearStencil: false
    });
    outline.draw(renderPass, {
      identifierTexture: channels.identifierTexture,
      selectedIdentifier,
      width: 2,
      color: [1, 0.6, 0.05, 1]
    });
    renderPass.end();
    graphicsDevice.submit();
  } finally {
    // Input ownership stays with the snapshot. Release only after submission.
    channels.destroy();
  }
}
// On application teardown, after submitting the overlay's final GPU use:
outline.destroy();

Draw option	Meaning
identifierTexture	Caller-owned sampled r32uint texture with zero for background.
selectedIdentifier	Exact uint32 texture value for the current snapshot. Zero disables the overlay.
width	Inward stroke width in output pixels, rounded down and clamped to 0–8; default 2. Zero disables the overlay.
color	Linear, straight-alpha RGBA; default opaque amber [1, 0.6, 0.05, 1]. The overlay premultiplies and blends over destination color.
viewportOrigin	Top-left destination viewport origin, default [0, 0]. Texture pixels map one-to-one to destination pixels.

draw(renderPass, options) encodes one fullscreen triangle and returns whether it drew. Use a color-preserving render pass with a viewport matching the ID texture's dimensions. For an offset viewport, also supply its origin. The overlay treats neighbors outside the ID image as background, so selected regions touching an image boundary receive a border. It checks up to eight neighboring pixels along each of the four screen axes; corners follow this four-axis inward-border convention. It does not scale ID textures or draw silhouettes through occluders.

Submit a draw before changing options on the same outline instance. The outline owns its model and uniform buffer; destroy() releases those resources and never destroys the borrowed ID texture. Submit the final use before destroying either resource.

The JSON playground captures current channels only while a ray-traced mark is selected. Selection is retained as a placement ID and re-resolved against each snapshot, so packed integer reordering does not select a different object. Capturing channels adds a full primary-ray traversal and allocates 28 bytes per output pixel; the outline adds one fullscreen draw with bounded texture lookups. Use DepthTextureCopy with the snapshot's projected depth for raster overlay occlusion. Raster ID production remains separate work.