macro-clips slice 7: button state transitions

- ButtonClip transitions are now editable in ButtonInstanceDialog
  (from/to/duration/easing) and persisted on the clip via the new
  store.setButtonClipTransitions action; transitions are shared by
  every instance of the button (clip-scoped, not instance-scoped).
- lerpProps exported from interpolate.ts so callers outside the
  sampler can blend two poses.
- useButtonRuntime tracks an active transition per instance plus a
  reactive transitionTick that pokes Vue computeds each frame.
  A self-driving RAF loop runs only while some transition is active
  (idles when none), so animations work paused or playing.
- applyButtonStateChange(id, to, transitions, persistedDisabled)
  is the one entry point for state changes — it looks up a matching
  from→to transition and starts it, or flips state instantly. Pointer
  handlers in CanvasStage and store.actionRuntime.setButtonState both
  go through it.
- CanvasStage blends the two state stacks via sampleStateLayers +
  blendStates: layers matched by name interpolate their sampled props
  with lerpProps; unmatched layers fade in/out. Renderer uses the
  blended layer list in place of the pure state stack during transit.
- Export runtime mirrors the same flow: applyButtonChange starts
  transitions, sampleButtonTransition drives per-frame progress, and
  drawButtonStatesBlended composites via drawLayer(layer, 0, override).
  drawLayer gained an optional propsOverride param for this.
  RUNTIME_VERSION bumped to 6.
- Tests cover applyButtonStateChange matching logic and
  sampleTransition's time → u mapping plus done flag.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/components/ButtonInstanceDialog.vue

@@ -1,11 +1,11 @@
 <script setup lang="ts">
 import { computed, ref, watch } from 'vue'
-import { PhTrash } from '@phosphor-icons/vue'
+import { PhPlus, PhTrash } from '@phosphor-icons/vue'
 import { useSceneStore } from '@/stores/scene'
 import { t } from '@/i18n'
 import { Modal } from '@/components/ui'
 import ActionEditor from './ActionEditor.vue'
-import type { Action } from '@/types/scene'
+import type { Action, ButtonState, Easing, StateTransition } from '@/types/scene'
 
 const props = defineProps<{
   modelValue: boolean
@@ -32,8 +32,12 @@ const buttonClip = computed(() => {
 const localLabel = ref('')
 const localDisabled = ref(false)
 const localActions = ref<Action[]>([])
+const localTransitions = ref<StateTransition[]>([])
 const labelError = ref<string | null>(null)
 
+const BUTTON_STATES: ButtonState[] = ['normal', 'hover', 'pressed', 'disabled']
+const EASINGS: Easing[] = ['linear', 'easeIn', 'easeOut', 'easeInOut']
+
 watch(
   [() => props.modelValue, () => props.instanceId],
   ([open, iid]) => {
@@ -43,6 +47,8 @@ watch(
     localLabel.value = bi.label ?? ''
     localDisabled.value = !!bi.disabled
     localActions.value = (bi.onClick ?? []).map((a) => ({ ...a }))
+    const clip = store.scene.buttonClips?.find((c) => c.id === bi.buttonClipId)
+    localTransitions.value = (clip?.transitions ?? []).map((t) => ({ ...t }))
     labelError.value = null
   },
   { immediate: true },
@@ -59,9 +65,30 @@ function commit(): boolean {
   }
   store.setButtonInstanceOnClick(props.instanceId, localActions.value)
   store.setButtonInstanceDisabled(props.instanceId, localDisabled.value)
+  const bi = store.scene.buttonInstances?.find((x) => x.id === props.instanceId)
+  if (bi) store.setButtonClipTransitions(bi.buttonClipId, localTransitions.value)
   return true
 }
 
+function addTransition() {
+  localTransitions.value = [
+    ...localTransitions.value,
+    { from: 'normal', to: 'hover', duration: 0.15, easing: 'easeOut' },
+  ]
+}
+
+function removeTransition(index: number) {
+  const next = [...localTransitions.value]
+  next.splice(index, 1)
+  localTransitions.value = next
+}
+
+function updateTransition(index: number, patch: Partial<StateTransition>) {
+  const next = [...localTransitions.value]
+  next[index] = { ...next[index], ...patch }
+  localTransitions.value = next
+}
+
 function close() {
   if (commit()) emit('update:modelValue', false)
 }
@@ -110,6 +137,50 @@ function removeInstance() {
           @update:actions="localActions = $event"
         />
       </div>
+      <div class="field">
+        <span class="field-label">
+          {{ t('buttonInstanceDialog.transitions') }}
+          <small class="field-hint">{{ t('buttonInstanceDialog.transitionsHint') }}</small>
+        </span>
+        <ol v-if="localTransitions.length" class="trans-list">
+          <li v-for="(tr, i) in localTransitions" :key="i" class="trans-row">
+            <select
+              :value="tr.from"
+              @change="updateTransition(i, { from: ($event.target as HTMLSelectElement).value as ButtonState })"
+            >
+              <option v-for="s in BUTTON_STATES" :key="s" :value="s">{{ s }}</option>
+            </select>
+            <span class="arrow">→</span>
+            <select
+              :value="tr.to"
+              @change="updateTransition(i, { to: ($event.target as HTMLSelectElement).value as ButtonState })"
+            >
+              <option v-for="s in BUTTON_STATES" :key="s" :value="s">{{ s }}</option>
+            </select>
+            <input
+              type="number"
+              step="0.01"
+              min="0"
+              :value="tr.duration"
+              @input="updateTransition(i, { duration: Number(($event.target as HTMLInputElement).value) })"
+              class="dur"
+            />
+            <select
+              :value="tr.easing"
+              @change="updateTransition(i, { easing: ($event.target as HTMLSelectElement).value as Easing })"
+            >
+              <option v-for="e in EASINGS" :key="e" :value="e">{{ e }}</option>
+            </select>
+            <button class="icon-btn danger" :title="t('actions.remove')" @click="removeTransition(i)">
+              <PhTrash :size="13" />
+            </button>
+          </li>
+        </ol>
+        <button class="add-btn" @click="addTransition">
+          <PhPlus :size="12" weight="bold" />
+          {{ t('buttonInstanceDialog.addTransition') }}
+        </button>
+      </div>
     </div>
     <template #footer>
       <button class="btn danger" @click="removeInstance">
@@ -215,4 +286,83 @@ function removeInstance() {
 .spacer {
   flex: 1;
 }
+
+.field-hint {
+  margin-left: 6px;
+  color: var(--text-dim);
+  font-weight: normal;
+  font-size: 10px;
+}
+
+.trans-list {
+  list-style: none;
+  padding: 0;
+  margin: 0 0 6px 0;
+  display: flex;
+  flex-direction: column;
+  gap: 4px;
+}
+
+.trans-row {
+  display: flex;
+  align-items: center;
+  gap: 4px;
+}
+
+.trans-row select,
+.trans-row input.dur {
+  background: var(--bg);
+  border: 1px solid var(--border);
+  color: var(--text);
+  padding: 3px 5px;
+  border-radius: var(--radius-sm);
+  font-size: 11px;
+  font-family: inherit;
+}
+
+.trans-row input.dur {
+  width: 56px;
+}
+
+.trans-row .arrow {
+  color: var(--text-dim);
+  font-size: 11px;
+}
+
+.icon-btn {
+  width: 22px;
+  height: 22px;
+  padding: 0;
+  display: inline-flex;
+  align-items: center;
+  justify-content: center;
+  background: var(--bg);
+  border: 1px solid var(--border);
+  border-radius: var(--radius-sm);
+  color: var(--text-dim);
+  cursor: pointer;
+}
+
+.icon-btn.danger:hover {
+  background: var(--danger-soft);
+  color: var(--danger);
+}
+
+.add-btn {
+  display: inline-flex;
+  align-items: center;
+  gap: 5px;
+  padding: 3px 9px;
+  background: var(--panel);
+  border: 1px dashed var(--border-strong);
+  color: var(--text);
+  border-radius: var(--radius-sm);
+  font-size: 11px;
+  align-self: flex-start;
+  cursor: pointer;
+}
+
+.add-btn:hover {
+  background: var(--panel-hover);
+}
 </style>

src/components/CanvasStage.vue

@@ -18,8 +18,12 @@ import type {
   Layer,
   Point,
 } from '@/types/scene'
-import { useButtonRuntime } from '@/composables/useButtonRuntime'
+import {
+  applyButtonStateChange,
+  useButtonRuntime,
+} from '@/composables/useButtonRuntime'
 import { evalAction } from '@/lib/actions'
+import { lerpProps } from '@/lib/interpolate'
 import { t } from '@/i18n'
 import { useKfSelection } from '@/composables/useKfSelection'
 import { showLocked } from '@/composables/useShowLocked'
@@ -208,23 +212,86 @@ interface ButtonRenderItem {
   hit: { width: number; height: number; offsetX: number; offsetY: number }
 }
 
+function sampleStateLayers(
+  clip: ButtonClip,
+  state: ButtonState,
+): ButtonRenderItem['layers'] {
+  const layers = clip.states[state] ?? []
+  const out: ButtonRenderItem['layers'] = []
+  for (const layer of layers) {
+    const asset = store.scene.assets.find((a) => a.id === layer.assetId)
+    if (!asset) continue
+    out.push({ layer, asset, props: sampleLayer(layer, 0) })
+  }
+  return out
+}
+
+/**
+ * Blend the "from" state's layers into the "to" state's layers by layer
+ * name. Matched pairs lerp their props; unmatched from-layers fade out,
+ * unmatched to-layers fade in.
+ */
+function blendStates(
+  clip: ButtonClip,
+  from: ButtonState,
+  to: ButtonState,
+  u: number,
+): ButtonRenderItem['layers'] {
+  const fromLayers = clip.states[from] ?? []
+  const toLayers = clip.states[to] ?? []
+  const fromByName = new Map<string, Layer>()
+  const toByName = new Map<string, Layer>()
+  for (const l of fromLayers) fromByName.set(l.name, l)
+  for (const l of toLayers) toByName.set(l.name, l)
+  const seen = new Set<string>()
+  const out: ButtonRenderItem['layers'] = []
+  // Preserve to-state order primarily, with unmatched from-layers pinned
+  // underneath so the new state visually rises into place.
+  for (const l of fromLayers) {
+    if (toByName.has(l.name)) continue
+    const asset = store.scene.assets.find((a) => a.id === l.assetId)
+    if (!asset) continue
+    const base = sampleLayer(l, 0)
+    out.push({ layer: l, asset, props: { ...base, opacity: base.opacity * (1 - u) } })
+  }
+  for (const l of toLayers) {
+    const asset = store.scene.assets.find((a) => a.id === l.assetId)
+    if (!asset) continue
+    seen.add(l.name)
+    const fromLayer = fromByName.get(l.name)
+    if (fromLayer) {
+      const a = sampleLayer(fromLayer, 0)
+      const b = sampleLayer(l, 0)
+      out.push({ layer: l, asset, props: lerpProps(a, b, u) })
+    } else {
+      const base = sampleLayer(l, 0)
+      out.push({ layer: l, asset, props: { ...base, opacity: base.opacity * u } })
+    }
+  }
+  void seen
+  return out
+}
+
 const activeButtonInstances = computed<ButtonRenderItem[]>(() => {
+  // Force re-evaluation on every transition RAF tick.
+  void buttonRt.transitionTick.value
   const out: ButtonRenderItem[] = []
   const instances = store.scene.buttonInstances ?? []
   const clips = store.scene.buttonClips ?? []
   const clipById = new Map(clips.map((c) => [c.id, c]))
+  const now = performance.now()
   for (const bi of instances) {
     if (store.playhead < bi.startTime) continue
     const clip = clipById.get(bi.buttonClipId)
     if (!clip) continue
     const disabled = buttonRt.isDisabled(bi.id, bi.disabled)
     const state = buttonRt.getState(bi.id, bi.disabled)
-    const layers = clip.states[state] ?? []
-    const rendered: ButtonRenderItem['layers'] = []
-    for (const layer of layers) {
-      const asset = store.scene.assets.find((a) => a.id === layer.assetId)
-      if (!asset) continue
-      rendered.push({ layer, asset, props: sampleLayer(layer, 0) })
+    const tr = buttonRt.sampleTransition(bi.id, now)
+    let rendered: ButtonRenderItem['layers']
+    if (tr && !tr.done && !disabled) {
+      rendered = blendStates(clip, tr.from, tr.to, tr.u)
+    } else {
+      rendered = sampleStateLayers(clip, state)
     }
     // Hit area: explicit hitArea on the clip, or fall back to the bbox of
     // the first rect-like asset in the normal state.
@@ -293,25 +360,30 @@ function buttonChildConfig<T extends Record<string, unknown>>(cfg: T): T {
   return { ...cfg, draggable: false, listening: false }
 }
 
+function transitionsFor(bi: ButtonInstance) {
+  return store.scene.buttonClips?.find((c) => c.id === bi.buttonClipId)?.transitions
+}
+
 function onButtonMouseEnter(bi: ButtonInstance) {
   const cur = buttonRt.getState(bi.id, bi.disabled)
-  if (cur === 'normal') buttonRt.setState(bi.id, 'hover')
+  if (cur === 'normal') applyButtonStateChange(bi.id, 'hover', transitionsFor(bi), bi.disabled)
 }
 
 function onButtonMouseLeave(bi: ButtonInstance) {
   const cur = buttonRt.getState(bi.id, bi.disabled)
-  if (cur === 'hover' || cur === 'pressed') buttonRt.setState(bi.id, 'normal')
+  if (cur === 'hover' || cur === 'pressed')
+    applyButtonStateChange(bi.id, 'normal', transitionsFor(bi), bi.disabled)
 }
 
 function onButtonMouseDown(bi: ButtonInstance) {
   const cur = buttonRt.getState(bi.id, bi.disabled)
-  if (cur === 'hover') buttonRt.setState(bi.id, 'pressed')
+  if (cur === 'hover') applyButtonStateChange(bi.id, 'pressed', transitionsFor(bi), bi.disabled)
 }
 
 function onButtonMouseUp(bi: ButtonInstance) {
   const cur = buttonRt.getState(bi.id, bi.disabled)
   if (cur !== 'pressed') return
-  buttonRt.setState(bi.id, 'hover')
+  applyButtonStateChange(bi.id, 'hover', transitionsFor(bi), bi.disabled)
   const actions = bi.onClick
   if (actions && actions.length) runButtonActions(actions)
 }

src/composables/useButtonRuntime.ts

@@ -1,5 +1,13 @@
-import { reactive } from 'vue'
-import type { ButtonState } from '@/types/scene'
+import { reactive, ref } from 'vue'
+import type { ButtonState, Easing, StateTransition } from '@/types/scene'
+
+export interface ActiveTransition {
+  from: ButtonState
+  to: ButtonState
+  startedAt: number
+  duration: number
+  easing: Easing
+}
 
 // Runtime-only per-instance state. Not persisted; resets on page reload.
 interface RuntimeState {
@@ -8,17 +16,81 @@ interface RuntimeState {
   // Runtime disabled flag — overrides (and can be overridden by) the
   // instance's persisted `disabled` field. Undefined = use persisted.
   disabled: Map<string, boolean>
+  // Currently-running transition per instance.
+  transition: Map<string, ActiveTransition>
 }
 
 const runtime: RuntimeState = reactive({
   state: new Map<string, ButtonState>(),
   disabled: new Map<string, boolean>(),
+  transition: new Map<string, ActiveTransition>(),
 })
 
+// Bumps whenever a transition is started/ended so Vue computeds tied to
+// transition progress can re-evaluate on the next frame.
+const transitionTick = ref(0)
+export function pokeTransitionTick() {
+  transitionTick.value++
+}
+
+// Self-driving RAF loop so transitions animate even while playback is
+// paused. Idles when no transitions are active.
+let rafId = 0
+function ensureTransitionLoop() {
+  if (rafId) return
+  const step = () => {
+    const now = performance.now()
+    let anyActive = false
+    for (const [id, tr] of runtime.transition) {
+      const elapsedSec = (now - tr.startedAt) / 1000
+      if (elapsedSec >= tr.duration) {
+        runtime.transition.delete(id)
+      } else {
+        anyActive = true
+      }
+    }
+    transitionTick.value++
+    rafId = anyActive ? requestAnimationFrame(step) : 0
+  }
+  rafId = requestAnimationFrame(step)
+}
+
+/**
+ * Change a button's state. If a matching from→to transition is defined
+ * on the clip, start the animated transition. Otherwise switch instantly.
+ */
+export function applyButtonStateChange(
+  id: string,
+  to: ButtonState,
+  transitions: StateTransition[] | undefined,
+  persistedDisabled: boolean | undefined,
+): void {
+  const rt = useButtonRuntime()
+  const from = rt.getState(id, persistedDisabled)
+  if (from === to) return
+  const match = transitions?.find((t) => t.from === from && t.to === to)
+  if (match && match.duration > 0) {
+    rt.startTransition(id, from, to, match.duration, match.easing, performance.now())
+  }
+  rt.setState(id, to)
+}
+
+function easingProgress(u: number, e: Easing): number {
+  if (u <= 0) return 0
+  if (u >= 1) return 1
+  if (e === 'easeIn') return u * u
+  if (e === 'easeOut') return 1 - (1 - u) * (1 - u)
+  if (e === 'easeInOut')
+    return u < 0.5 ? 2 * u * u : 1 - Math.pow(-2 * u + 2, 2) / 2
+  return u
+}
+
 export function useButtonRuntime() {
   return {
     state: runtime.state,
     disabled: runtime.disabled,
+    transition: runtime.transition,
+    transitionTick,
     getState(id: string, persistedDisabled?: boolean): ButtonState {
       const override = runtime.disabled.get(id)
       const effectiveDisabled =
@@ -40,9 +112,48 @@ export function useButtonRuntime() {
     clearDisabled(id: string) {
       runtime.disabled.delete(id)
     },
+    /**
+     * Start a transition between two states; caller supplies performance.now()
+     * as `startedAt` so the runtime can interpolate without re-reading time.
+     */
+    startTransition(
+      id: string,
+      from: ButtonState,
+      to: ButtonState,
+      duration: number,
+      easing: Easing,
+      startedAt: number,
+    ) {
+      runtime.transition.set(id, { from, to, startedAt, duration, easing })
+      transitionTick.value++
+      if (duration > 0) ensureTransitionLoop()
+    },
+    /**
+     * Return interpolated progress u ∈ [0..1] (easing applied) + raw for the
+     * given instance's transition at `now`. If the transition has ended,
+     * returns { done: true, u: 1 }. Returns null if no active transition.
+     */
+    sampleTransition(id: string, now: number): {
+      u: number
+      from: ButtonState
+      to: ButtonState
+      done: boolean
+    } | null {
+      const t = runtime.transition.get(id)
+      if (!t) return null
+      const dur = Math.max(0.0001, t.duration)
+      const raw = (now - t.startedAt) / 1000 / dur
+      if (raw >= 1) return { u: 1, from: t.from, to: t.to, done: true }
+      return { u: easingProgress(raw, t.easing), from: t.from, to: t.to, done: false }
+    },
+    endTransition(id: string) {
+      if (runtime.transition.delete(id)) transitionTick.value++
+    },
     reset() {
       runtime.state.clear()
       runtime.disabled.clear()
+      runtime.transition.clear()
+      transitionTick.value++
     },
   }
 }

src/devtools/tests.ts

@@ -1,6 +1,9 @@
 import { createApp, h, nextTick, type Component, type Slot } from 'vue'
 import { createBlankScene, useSceneStore } from '@/stores/scene'
-import { useButtonRuntime } from '@/composables/useButtonRuntime'
+import {
+  applyButtonStateChange,
+  useButtonRuntime,
+} from '@/composables/useButtonRuntime'
 import {
   buildMarkerMap,
   evalAction,
@@ -3543,6 +3546,41 @@ export function registerAllTests(): void {
       expect(rt.getState('b1', false)).toBe('disabled')
     })
 
+    test('applyButtonStateChange starts a transition only when one matches', () => {
+      const rt = useButtonRuntime()
+      rt.reset()
+      // No transitions defined: state flips instantly, no transition entry.
+      applyButtonStateChange('b1', 'hover', undefined, undefined)
+      expect(rt.getState('b1')).toBe('hover')
+      expect(rt.transition.has('b1')).toBe(false)
+      // With a matching transition: flip state AND start transition.
+      rt.reset()
+      applyButtonStateChange(
+        'b1',
+        'hover',
+        [{ from: 'normal', to: 'hover', duration: 0.2, easing: 'easeOut' }],
+        undefined,
+      )
+      expect(rt.getState('b1')).toBe('hover')
+      expect(rt.transition.has('b1')).toBe(true)
+      rt.endTransition('b1')
+    })
+
+    test('sampleTransition returns null outside of transitions, u∈[0..1] within', () => {
+      const rt = useButtonRuntime()
+      rt.reset()
+      expect(rt.sampleTransition('b1', performance.now())).toBe(null)
+      const t0 = performance.now()
+      rt.startTransition('b1', 'normal', 'hover', 1, 'linear', t0)
+      const mid = rt.sampleTransition('b1', t0 + 500)!
+      expect(mid.done).toBe(false)
+      expect(mid.u > 0.4 && mid.u < 0.6).toBe(true)
+      const end = rt.sampleTransition('b1', t0 + 1100)!
+      expect(end.done).toBe(true)
+      expect(end.u).toBe(1)
+      rt.endTransition('b1')
+    })
+
     test('store.actionRuntime resolves labels and drives useButtonRuntime', () => {
       const s = makeFreshStore()
       const rt = useButtonRuntime()

src/i18n/messages.ts

@@ -423,6 +423,9 @@ export const en = {
     labelCollision: 'Label "{name}" is already used by another button instance.',
     disabled: 'Start disabled',
     onClick: 'On click',
+    transitions: 'Transitions',
+    transitionsHint: '(shared by all instances of this button)',
+    addTransition: 'Add transition',
     remove: 'Delete instance',
     done: 'Done',
   },

src/lib/exportPlayer.ts

@@ -1,6 +1,6 @@
 import type { Scene } from '@/types/scene'
 
-const RUNTIME_VERSION = '5'
+const RUNTIME_VERSION = '6'
 
 const ENGINE_SOURCE = `(function(){
   if (window.AnimatrPlayer && window.AnimatrPlayer.__v === '${RUNTIME_VERSION}') return;
@@ -223,6 +223,78 @@ const ENGINE_SOURCE = `(function(){
       if(st==='normal') delete runtime.buttonStates[id];
       else runtime.buttonStates[id]=st;
     }
+    var buttonTransitions={}; // id -> { from, to, startedAt, duration, easing }
+    function startButtonTransition(id, from, to, duration, easing){
+      buttonTransitions[id]={from:from, to:to, startedAt:performance.now(), duration:duration, easing:easing};
+    }
+    function easingProgressRt(u, e){
+      if(u<=0) return 0; if(u>=1) return 1;
+      if(e==='easeIn') return u*u;
+      if(e==='easeOut') return 1-(1-u)*(1-u);
+      if(e==='easeInOut') return u<0.5?2*u*u:1-Math.pow(-2*u+2,2)/2;
+      return u;
+    }
+    function sampleButtonTransition(id){
+      var tr=buttonTransitions[id]; if(!tr) return null;
+      var dur=Math.max(0.0001, tr.duration);
+      var raw=(performance.now()-tr.startedAt)/1000/dur;
+      if(raw>=1){ delete buttonTransitions[id]; return { u:1, from:tr.from, to:tr.to, done:true }; }
+      return { u:easingProgressRt(raw, tr.easing), from:tr.from, to:tr.to, done:false };
+    }
+    function applyButtonChange(bi, clip, to){
+      var from=getEffectiveButtonState(bi);
+      if(from===to) return;
+      var trs=clip.transitions||[];
+      for(var ti=0; ti<trs.length; ti++){
+        if(trs[ti].from===from && trs[ti].to===to && trs[ti].duration>0){
+          startButtonTransition(bi.id, from, to, trs[ti].duration, trs[ti].easing);
+          break;
+        }
+      }
+      setButtonState(bi.id, to);
+    }
+    function lerpScalar(a,b,t){return a+(b-a)*t;}
+    function lerpRuntimeProps(a,b,t){
+      var out={
+        x:lerpScalar(a.x,b.x,t),
+        y:lerpScalar(a.y,b.y,t),
+        scaleX:lerpScalar(a.scaleX,b.scaleX,t),
+        scaleY:lerpScalar(a.scaleY,b.scaleY,t),
+        rotation:lerpScalar(a.rotation,b.rotation,t),
+        opacity:lerpScalar(a.opacity,b.opacity,t)
+      };
+      if(a.fill&&b.fill) out.fill=lerpColor(a.fill,b.fill,t);
+      else if(b.fill) out.fill=b.fill;
+      else if(a.fill) out.fill=a.fill;
+      return out;
+    }
+    function drawButtonStatesBlended(clip, from, to, u){
+      var fromLs=(clip.states&&clip.states[from])||[];
+      var toLs=(clip.states&&clip.states[to])||[];
+      var toByName={};
+      for(var ii=0; ii<toLs.length; ii++) toByName[toLs[ii].name]=toLs[ii];
+      var fromByName={};
+      for(var ij=0; ij<fromLs.length; ij++) fromByName[fromLs[ij].name]=fromLs[ij];
+      // Unmatched from-layers fade out.
+      for(var fi=0; fi<fromLs.length; fi++){
+        var fl=fromLs[fi];
+        if(toByName[fl.name]) continue;
+        var flp=sample(fl,0);
+        drawLayer(fl, 0, { opacity: flp.opacity*(1-u) });
+      }
+      for(var ti2=0; ti2<toLs.length; ti2++){
+        var tl=toLs[ti2];
+        var fm=fromByName[tl.name];
+        if(fm){
+          var ap=sample(fm,0);
+          var bp=sample(tl,0);
+          drawLayer(tl, 0, lerpRuntimeProps(ap,bp,u));
+        } else {
+          var tlp=sample(tl,0);
+          drawLayer(tl, 0, { opacity: tlp.opacity*u });
+        }
+      }
+    }
     function pointerToSceneXY(e){
       var rc=canvas.getBoundingClientRect();
       var lw=scene.canvas.width, lh=scene.canvas.height;
@@ -242,20 +314,25 @@ const ENGINE_SOURCE = `(function(){
       }
       return null;
     }
+    function findClipForInstance(bi){
+      var cs=scene.buttonClips||[];
+      for(var i=0;i<cs.length;i++) if(cs[i].id===bi.buttonClipId) return cs[i];
+      return null;
+    }
     function onStageMove(e){
       var p=pointerToSceneXY(e);
       if(!p) return;
       var hit=hitButtonAt(p);
       for(var i=0;i<buttonHits.length;i++){
         var bh=buttonHits[i];
-        var isDis=getEffectiveButtonState(bh.bi)==='disabled';
-        if(isDis) continue;
+        if(getEffectiveButtonState(bh.bi)==='disabled') continue;
+        var clip=findClipForInstance(bh.bi);
+        if(!clip) continue;
         if(hit && hit.bi.id===bh.bi.id){
-          var cur=getEffectiveButtonState(bh.bi);
-          if(cur==='normal') setButtonState(bh.bi.id,'hover');
+          if(getEffectiveButtonState(bh.bi)==='normal') applyButtonChange(bh.bi, clip, 'hover');
         } else {
-          var cur2=getEffectiveButtonState(bh.bi);
-          if(cur2==='hover'||cur2==='pressed') setButtonState(bh.bi.id,'normal');
+          var cur=getEffectiveButtonState(bh.bi);
+          if(cur==='hover'||cur==='pressed') applyButtonChange(bh.bi, clip, 'normal');
         }
       }
     }
@@ -265,7 +342,8 @@ const ENGINE_SOURCE = `(function(){
       var hit=hitButtonAt(p);
       if(!hit) return;
       if(getEffectiveButtonState(hit.bi)==='disabled') return;
-      setButtonState(hit.bi.id,'pressed');
+      var clip=findClipForInstance(hit.bi);
+      if(clip) applyButtonChange(hit.bi, clip, 'pressed');
     }
     function onStageUp(e){
       var p=pointerToSceneXY(e);
@@ -275,7 +353,8 @@ const ENGINE_SOURCE = `(function(){
         if(getEffectiveButtonState(bh.bi)!=='pressed') continue;
         var lx=p.x-(bh.bi.x||0), ly=p.y-(bh.bi.y||0);
         var inside=lx>=bh.hit.left&&lx<=bh.hit.right&&ly>=bh.hit.top&&ly<=bh.hit.bottom;
-        setButtonState(bh.bi.id, inside?'hover':'normal');
+        var clip=findClipForInstance(bh.bi);
+        if(clip) applyButtonChange(bh.bi, clip, inside?'hover':'normal');
         if(inside){
           var acts=bh.bi.onClick||[];
           for(var ai=0; ai<acts.length; ai++) evalAction(acts[ai]);
@@ -356,7 +435,15 @@ const ENGINE_SOURCE = `(function(){
         case 'setButtonState': {
           var sid=resolveButtonRef(act.instanceId);
           if(!sid){ runtime.warn('Unknown button ref: '+act.instanceId); return; }
-          runtime.buttonStates[sid]=act.state;
+          var sBi=null, sClip=null;
+          var sBis=scene.buttonInstances||[];
+          for(var sbI=0; sbI<sBis.length; sbI++) if(sBis[sbI].id===sid){ sBi=sBis[sbI]; break; }
+          if(sBi){
+            var sClips=scene.buttonClips||[];
+            for(var scI=0; scI<sClips.length; scI++) if(sClips[scI].id===sBi.buttonClipId){ sClip=sClips[scI]; break; }
+          }
+          if(sBi && sClip) applyButtonChange(sBi, sClip, act.state);
+          else setButtonState(sid, act.state);
           return;
         }
         case 'setButtonDisabled': {
@@ -486,10 +573,11 @@ const ENGINE_SOURCE = `(function(){
       }
       ctxm.restore();
     }
-    function drawLayer(layer,time){
+    function drawLayer(layer,time,propsOverride){
       var asset=assetMap[layer.assetId];
       if(!asset||!layer.visible)return;
       var p=sample(layer,time);
+      if(propsOverride){ for(var poKey in propsOverride) p[poKey]=propsOverride[poKey]; }
       ctx.save();
       ctx.globalAlpha=ctx.globalAlpha*p.opacity;
       ctx.translate(p.x,p.y);
@@ -732,11 +820,16 @@ const ENGINE_SOURCE = `(function(){
         var bclp=bClipById[bi.buttonClipId];
         if(!bclp) continue;
         var bst=getEffectiveButtonState(bi);
-        var bStack=(bclp.states&&bclp.states[bst])||[];
+        var btr=sampleButtonTransition(bi.id);
         var bx=bi.x||0, by=bi.y||0;
         ctx.save();
         ctx.translate(bx, by);
-        for(var blI=0; blI<bStack.length; blI++) drawLayer(bStack[blI], 0);
+        if(btr && !btr.done && bst!=='disabled'){
+          drawButtonStatesBlended(bclp, btr.from, btr.to, btr.u);
+        } else {
+          var bStack=(bclp.states&&bclp.states[bst])||[];
+          for(var blI=0; blI<bStack.length; blI++) drawLayer(bStack[blI], 0);
+        }
         ctx.restore();
         // Hit rect: explicit hitArea on clip, else bbox of first rect/circle
         // layer in the normal state.

src/lib/interpolate.ts

@@ -37,7 +37,7 @@ export function lerpColor(a: string, b: string, t: number): string {
   return formatHex(lerp(pa[0], pb[0], t), lerp(pa[1], pb[1], t), lerp(pa[2], pb[2], t))
 }
 
-function lerpProps(a: AnimatableProps, b: AnimatableProps, t: number): AnimatableProps {
+export function lerpProps(a: AnimatableProps, b: AnimatableProps, t: number): AnimatableProps {
   const out: AnimatableProps = {
     x: lerp(a.x, b.x, t),
     y: lerp(a.y, b.y, t),

src/stores/scene.ts

@@ -27,7 +27,10 @@ import {
   scriptFramesInRange,
   type ActionRuntime,
 } from '@/lib/actions'
-import { useButtonRuntime } from '@/composables/useButtonRuntime'
+import {
+  applyButtonStateChange,
+  useButtonRuntime,
+} from '@/composables/useButtonRuntime'
 
 const uid = () => Math.random().toString(36).slice(2, 10)
 
@@ -1204,6 +1207,15 @@ export const useSceneStore = defineStore('scene', {
       const clip = this.scene.buttonClips?.find((c) => c.id === id)
       if (clip) clip.name = name.trim() || clip.name
     },
+    setButtonClipTransitions(
+      id: string,
+      transitions: NonNullable<ButtonClip['transitions']>,
+    ) {
+      const clip = this.scene.buttonClips?.find((c) => c.id === id)
+      if (!clip) return
+      if (transitions.length) clip.transitions = [...transitions]
+      else delete clip.transitions
+    },
     addButtonInstance(
       buttonClipId: string,
       clipTrackId: string,
@@ -1577,7 +1589,11 @@ export const useSceneStore = defineStore('scene', {
             console.warn('[animatr] unknown button ref:', ref)
             return
           }
-          btnRt.setState(id, state)
+          const inst = instances.find((x) => x.id === id)
+          const clip = self.scene.buttonClips?.find(
+            (c) => c.id === inst?.buttonClipId,
+          )
+          applyButtonStateChange(id, state, clip?.transitions, inst?.disabled)
         },
         setButtonDisabled(ref, disabled) {
           const id = resolve(ref)