fix: refine avatar accessory occlusion

packages/avatar-core/src/geometry.ts

@@ -1382,7 +1382,7 @@ const headPath = (pose: AvatarPose, surface: SurfaceConfig) => {
   return path(convexHull(projectedSamples))
 }
 
-const accessoryPath = (pose: AvatarPose, node: BodyNode) => {
+const accessoryGeometry = (pose: AvatarPose, node: BodyNode) => {
   const key = surfaceCacheKey(node.surface)
   let localSamples = accessorySamplesCache.get(key)
   if (!localSamples) {
@@ -1415,11 +1415,13 @@ const accessoryPath = (pose: AvatarPose, node: BodyNode) => {
     (node.surface.type === 'cube' || node.surface.type === 'diamond') &&
     node.surface.roundness <= 0
   ) {
-    return path(hull)
+    return { hull, path: path(hull) }
   }
-  return smoothClosedPath(densifyClosedPoints(hull))
+  return { hull, path: smoothClosedPath(densifyClosedPoints(hull)) }
 }
 
+type Point2 = readonly [number, number]
+
 const ACCESSORY_FRONT_CROSSING_RATIO = 0.1
 
 const accessoryCameraDepthRadius = (pose: AvatarPose, node: BodyNode) => {
@@ -1444,17 +1446,82 @@ const accessoryCameraDepthRadius = (pose: AvatarPose, node: BodyNode) => {
   )
 }
 
-const accessoryLayers = (pose: AvatarPose, nodes: BodyNode[]) => {
+const polygonSignedArea = (points: readonly Point2[]) =>
+  points.reduce((total, point, index) => {
+    const next = points[(index + 1) % points.length]
+    return total + point[0] * next[1] - next[0] * point[1]
+  }, 0) / 2
+
+const convexPolygonIntersection = (subject: Point2[], clip: Point2[]) => {
+  let output = subject
+  const orientation = Math.sign(polygonSignedArea(clip)) || 1
+  const inside = (point: Point2, start: Point2, end: Point2) =>
+    orientation *
+      ((end[0] - start[0]) * (point[1] - start[1]) - (end[1] - start[1]) * (point[0] - start[0])) >=
+    0
+  const crossing = (from: Point2, to: Point2, start: Point2, end: Point2): Point2 => {
+    const deltaX = to[0] - from[0]
+    const deltaY = to[1] - from[1]
+    const edgeX = end[0] - start[0]
+    const edgeY = end[1] - start[1]
+    const denominator = deltaX * edgeY - deltaY * edgeX
+    const amount =
+      denominator === 0
+        ? 0
+        : ((start[0] - from[0]) * edgeY - (start[1] - from[1]) * edgeX) / denominator
+    return [from[0] + amount * deltaX, from[1] + amount * deltaY]
+  }
+
+  clip.forEach((start, index) => {
+    const end = clip[(index + 1) % clip.length]
+    const input = output
+    output = []
+    input.forEach((current, currentIndex) => {
+      const previous = input[(currentIndex + input.length - 1) % input.length]
+      const currentInside = inside(current, start, end)
+      const previousInside = inside(previous, start, end)
+      if (currentInside) {
+        if (!previousInside) output.push(crossing(previous, current, start, end))
+        output.push(current)
+      } else if (previousInside) {
+        output.push(crossing(previous, current, start, end))
+      }
+    })
+  })
+  return output
+}
+
+const AUTO_ACCESSORY_EYE_OCCLUSION_RATIO = 0.08
+
+const eyeOcclusionRatio = (accessory: Point2[], eye: Point2[]) => {
+  const eyeArea = Math.abs(polygonSignedArea(eye))
+  if (eyeArea === 0) return 0
+  return Math.abs(polygonSignedArea(convexPolygonIntersection(eye, accessory))) / eyeArea
+}
+
+const accessoryLayers = (pose: AvatarPose, nodes: BodyNode[], visibleEyes: Point2[][]) => {
   const layers = nodes
     .map(node => {
       const depth = rotateWithQuaternion(pose.orientation, node.position)[2]
+      const geometry = accessoryGeometry(pose, node)
+      const stronglyOccludesEye =
+        node.layer === 'auto' &&
+        visibleEyes.some(
+          eye =>
+            eyeOcclusionRatio(
+              geometry.hull.map(point => [point[0], point[1]] as Point2),
+              eye
+            ) >= AUTO_ACCESSORY_EYE_OCCLUSION_RATIO
+        )
       return {
         id: node.id,
-        path: accessoryPath(pose, node),
+        path: geometry.path,
         depth,
         front:
           node.layer === 'front' ||
-          (node.layer !== 'back' &&
+          (node.layer === 'auto'
+            ? !stronglyOccludesEye
+            : node.layer !== 'back' &&
               depth > accessoryCameraDepthRadius(pose, node) * ACCESSORY_FRONT_CROSSING_RATIO),
       }
     })
@@ -1477,7 +1544,12 @@ export const renderAvatar = (
   const rightSamples = eyePoints(pose, surface, 1, blink, options.eyeOffset)
   const left = leftSamples.map(sample => sample.point)
   const right = rightSamples.map(sample => sample.point)
-  const accessories = accessoryLayers(pose, options.bodyNodes ?? [])
+  const leftVisible = leftSamples.reduce((total, sample) => total + sample.normal[2], 0) > 0
+  const rightVisible = rightSamples.reduce((total, sample) => total + sample.normal[2], 0) > 0
+  const visibleEyes = [leftVisible ? left : null, rightVisible ? right : null]
+    .filter((eye): eye is Point3[] => eye !== null)
+    .map(eye => eye.map(point => [point[0], point[1]] as Point2))
+  const accessories = accessoryLayers(pose, options.bodyNodes ?? [], visibleEyes)
   const compositePaths = compositeBackPaths(pose, surface)
   return {
     backPaths: [...compositePaths, ...accessories.backPaths],
@@ -1487,8 +1559,8 @@ export const renderAvatar = (
     headPath: headPath(pose, surface),
     leftPath: path(left),
     rightPath: path(right),
-    leftVisible: leftSamples.reduce((total, sample) => total + sample.normal[2], 0) > 0,
+    leftVisible,
-    rightVisible: rightSamples.reduce((total, sample) => total + sample.normal[2], 0) > 0,
+    rightVisible,
     wirePaths: options.includeWire === false ? [] : wirePaths(pose, surface),
   }
 }

src/features/avatar/__tests__/avatars-test.ts

@@ -85,10 +85,10 @@ describe('OneWorks animal construction', () => {
       library.avatars.find(avatar => avatar.id === id)?.body.nodes.map(node => node.layer)
 
     expect(layers('oneworks-cat')).toBeUndefined()
-    expect(layers('oneworks-dog')).toEqual(['front', 'front'])
+    expect(layers('oneworks-dog')).toEqual(['auto', 'auto'])
     expect(layers('oneworks-bear')).toEqual(['back', 'back'])
     expect(layers('oneworks-rabbit')).toEqual(['back', 'back'])
-    expect(layers('oneworks-bun')).toEqual(['front'])
+    expect(layers('oneworks-bun')).toEqual(['back'])
   })
 
   it('keeps the unfinished piglet hidden and removes a persisted copy', () => {
@@ -153,7 +153,7 @@ describe('OneWorks animal construction', () => {
       avatar => avatar.id === 'oneworks-dog'
     )!
 
-    expect(dog.body.nodes.map(node => node.layer)).toEqual(['front', 'front'])
+    expect(dog.body.nodes.map(node => node.layer)).toEqual(['auto', 'auto'])
     expect(dog.body.nodes.map(node => node.position)).toEqual([
       [-82, -65, 0],
       [82, -65, 0],

src/features/avatar/avatars.ts

@@ -746,7 +746,7 @@ const oneWorksBundledAvatars: StudioAvatar[] = [
       nodes: [
         oneWorksNode('bun-crown', 'Rounded bun crown', 'cone', [0, -46, -14], 0.5, 0.23, {
           scaleZ: 0.5,
-          layer: 'front',
+          layer: 'back',
           surface: { roundness: 0.92, topScale: 0.82 },
         }),
       ],

src/features/avatar/components/ExpressionWorkspace.tsx

@@ -32,6 +32,7 @@ import {
   avatarBodyOutlineWidth,
   resolveAvatarNodeColor,
   useAvatarBodyColorOverride,
+  useRenderedSceneNodeOrder,
 } from '@/features/rendering/avatarAppearance'
 import {
   LivePixelAvatarCanvas,
@@ -199,6 +200,7 @@ export function LiveExpressionPreview({
   expressionBodyColor?: string
   id: string
 }) {
+  useRenderedSceneNodeOrder(scene)
   const bodyColorIsOverridden = useAvatarBodyColorOverride(colors.body, baseBodyColor)
 
   if (renderStyle.type === 'pixel') {

src/features/rendering/__tests__/rendered-scene-test.ts

@@ -39,6 +39,7 @@ describe('rendered avatar scene', () => {
       bodyNodes: [node],
     })
     const scene = createRenderedScene(first)
+    const initialNodeOrderVersion = scene.nodeOrderVersion.get()
     const rotated = renderAvatar(
       poseFromExpression({ ...defaultExpression, headY: 35 }),
       surfacePresets.sphere,
@@ -51,6 +52,11 @@ describe('rendered avatar scene', () => {
     expect(findBodyNodePath(scene, 'primary')).toBe(scene.headPath)
     expect(findBodyNodePath(scene, node.id)).not.toBeNull()
     expect(scene.headPath.get()).toBe(rotated.headPath)
+    expect(scene.nodeOrderVersion.get()).toBeGreaterThan(initialNodeOrderVersion)
+
+    const stableNodeOrderVersion = scene.nodeOrderVersion.get()
+    paintRenderedScene(scene, rotated)
+    expect(scene.nodeOrderVersion.get()).toBe(stableNodeOrderVersion)
   })
 
   it('updates animated colors without replacing their motion values', () => {
@@ -98,13 +104,11 @@ describe('rendered avatar scene', () => {
     expect(forcedFront.frontNodeIds).toContain(avatar.body.nodes[0].id)
   })
 
-  it('moves dog ears between front and back with head depth', () => {
+  it('moves a dog ear behind the head only when it strongly overlaps an eye', () => {
     const studio = loadStudioDocument({ getItem: () => null })
     const avatar = studio.library.avatars.find(item => item.id === 'oneworks-dog')!
     const detachedEars: string[] = []
 
-    let splitDepthExpressions = 0
-
     studio.expressions.forEach(expression => {
       const geometry = renderAvatar(
         poseFromExpression(expression as Expression),
@@ -115,12 +119,6 @@ describe('rendered avatar scene', () => {
       const head = pathBounds(geometry.headPath)
 
       const earIds = ['dog-ear-left', 'dog-ear-right'] as const
-      if (
-        geometry.frontNodeIds.some(id => earIds.includes(id as (typeof earIds)[number])) &&
-        geometry.backNodeIds.some(id => earIds.includes(id as (typeof earIds)[number]))
-      ) {
-        splitDepthExpressions += 1
-      }
       earIds.forEach(nodeId => {
         const frontIndex = geometry.frontNodeIds.indexOf(nodeId)
         const backIndex = geometry.backNodeIds.indexOf(nodeId)
@@ -137,8 +135,25 @@ describe('rendered avatar scene', () => {
       })
     })
 
-    expect(splitDepthExpressions).toBeGreaterThan(0)
     expect(detachedEars, 'detached dog ears').toEqual([])
+
+    const expressionById = new Map(
+      studio.expressions.map(expression => [expression.id, expression])
+    )
+    const geometryFor = (sequenceId: string) => {
+      const sequence = studio.sequences.find(item => item.id === sequenceId)!
+      const expression = expressionById.get(sequence.steps[0].expressionId) as Expression
+      return renderAvatar(poseFromExpression(expression), avatar.body.primary as SurfaceConfig, 1, {
+        bodyNodes: avatar.body.nodes as BodyNode[],
+      })
+    }
+
+    ;['idle', 'shy', 'proud'].forEach(sequenceId => {
+      expect(geometryFor(sequenceId).backNodeIds, sequenceId).toContain('dog-ear-right')
+    })
+    expect(geometryFor('angry').frontNodeIds).toEqual(
+      expect.arrayContaining(['dog-ear-left', 'dog-ear-right'])
+    )
   })
 
   it('keeps bear ears attached behind the head across expressions', () => {

src/features/rendering/avatarAppearance.ts

@@ -1,6 +1,8 @@
 import { useMotionValueEvent, type MotionValue } from 'motion/react'
 import { useEffect, useState } from 'react'
 
+import type { RenderedScene } from './renderedScene'
+
 export const avatarBodyOutlineWidth = () => 12
 
 const colorsMatch = (left: string, right: string) =>
@@ -26,6 +28,14 @@ export const useAvatarBodyColorOverride = (
   return overridden
 }
 
+export const useRenderedSceneNodeOrder = (scene: RenderedScene) => {
+  const [, setVersion] = useState(0)
+
+  useMotionValueEvent(scene.nodeOrderVersion, 'change', () => {
+    setVersion(version => version + 1)
+  })
+}
+
 export const resolveAvatarNodeColor = ({
   nodeColor,
   bodyColor,

src/features/rendering/components/AvatarCanvas.tsx

@@ -44,6 +44,7 @@ import {
 } from '@/features/avatar/manipulationSession'
 import { type SurfaceConfig } from '@/features/avatar/surfaces'
 import { type CanvasPreviewTarget } from '@/features/rendering/canvasPreview'
+import { useRenderedSceneNodeOrder } from '@/features/rendering/avatarAppearance'
 import { LivePixelAvatarCanvas } from '@/features/rendering/components/PixelAvatarCanvas'
 import { type RenderedRotationGizmo } from '@/features/rendering/renderedRotationGizmo'
 import {
@@ -550,6 +551,7 @@ export function AvatarCanvas({
   onManipulationStart: () => Expression
 }) {
   const { t } = useStudioLanguage()
+  useRenderedSceneNodeOrder(scene)
   const {
     wirePaths,
     backPaths,

src/features/rendering/renderedScene.ts

@@ -10,6 +10,7 @@ export type RenderedScene = {
   frontPaths: MotionValue<string>[]
   backNodeIds: { current: (string | null)[] }
   frontNodeIds: { current: (string | null)[] }
+  nodeOrderVersion: MotionValue<number>
   leftPath: MotionValue<string>
   rightPath: MotionValue<string>
   leftOpacity: MotionValue<number>
@@ -36,6 +37,7 @@ export const createRenderedScene = (geometry: AvatarGeometry): RenderedScene =>
   ),
   backNodeIds: { current: geometry.backNodeIds },
   frontNodeIds: { current: geometry.frontNodeIds },
+  nodeOrderVersion: motionValue(0),
   leftPath: motionValue(geometry.leftPath),
   rightPath: motionValue(geometry.rightPath),
   leftOpacity: motionValue(geometry.leftVisible ? 1 : 0),
@@ -62,8 +64,14 @@ export const paintRenderedOffset = (scene: RenderedScene, offset: { x: number; y
 
 export const paintRenderedScene = (scene: RenderedScene, geometry: AvatarGeometry) => {
   scene.headPath.set(geometry.headPath)
+  const nodeOrderChanged =
+    scene.backNodeIds.current.length !== geometry.backNodeIds.length ||
+    scene.frontNodeIds.current.length !== geometry.frontNodeIds.length ||
+    scene.backNodeIds.current.some((id, index) => id !== geometry.backNodeIds[index]) ||
+    scene.frontNodeIds.current.some((id, index) => id !== geometry.frontNodeIds[index])
   scene.backNodeIds.current = geometry.backNodeIds
   scene.frontNodeIds.current = geometry.frontNodeIds
+  if (nodeOrderChanged) scene.nodeOrderVersion.set(scene.nodeOrderVersion.get() + 1)
   scene.backPaths.forEach((path, index) => path.set(geometry.backPaths[index] ?? ''))
   scene.frontPaths.forEach((path, index) => path.set(geometry.frontPaths[index] ?? ''))
   scene.leftPath.set(geometry.leftPath)

src/features/studio/components/AvatarDrawer.tsx

@@ -15,6 +15,7 @@ import { defaultExpression } from '@/features/avatar/presets'
 import {
   avatarBodyOutlineWidth,
   useAvatarBodyColorOverride,
+  useRenderedSceneNodeOrder,
 } from '@/features/rendering/avatarAppearance'
 import { LivePixelAvatarCanvas } from '@/features/rendering/components/PixelAvatarCanvas'
 import type { RenderedColors, RenderedScene } from '@/features/rendering/renderedScene'
@@ -31,6 +32,7 @@ function LiveAvatarPreview({
   scene: RenderedScene
   expressionBodyColor?: string
 }) {
+  useRenderedSceneNodeOrder(scene)
   const outlineWidth = avatarBodyOutlineWidth()
   const filled = avatar.renderStyle.type === 'vector' && avatar.renderStyle.filled === true
   const fixedSkinColors =

src/features/studio/useStudioController.ts

@@ -1573,12 +1573,7 @@ export function useStudioController() {
     activeSequence && playbackVisual.position !== null
       ? expressionById.get(activeSequence.steps[playbackVisual.position]?.expressionId ?? '')
       : null
-  const activeSequenceUsesBodyColor =
+  const renderedExpressionBodyColor = playbackExpression?.bodyColor ?? expression.bodyColor
-    activeSequence?.steps.some(step => expressionById.get(step.expressionId)?.bodyColor) ?? false
-  const renderedExpressionBodyColor =
-    playbackExpression?.bodyColor ??
-    expression.bodyColor ??
-    (activeSequenceUsesBodyColor ? renderedColors.body.get() : undefined)
   const semanticKeyIssueMessage = (issue: SemanticKeyIssueCode | 'duplicate_semantic_key') =>
     t(
       issue === 'missing_semantic_key'