Play animation's blend is given in seconds, not in frames of the new animation (#106)

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

src/core/model/animation.ts

@@ -392,20 +392,21 @@ export interface AnimationPlayer {
 }
 
 /**
- * A crossfade into a player that just took over (#106): over `frames` of its own, a row that blends
- * mixes from what the property held into the player's value. `from` is taken on the first tick of the
- * blend; a property an earlier player writes in the same tick is mixed from that value instead, live.
+ * A crossfade into a player that just took over (#106): over `seconds`, whatever the animation's frame
+ * rate, a row that blends mixes from what the property held into the player's value. `from` is taken
+ * on the first tick of the blend; a property an earlier player writes in the same tick is mixed from
+ * that value instead, live.
  */
 export interface AnimationBlend {
-  frames: number;
+  seconds: number;
   elapsed: number;
   from?: Record<string, PropertyValue>;
 }
 
-/** How far a blend has come, 0…1; an animation without a frame rate has nothing to blend over. */
-export function blendShare(blend: AnimationBlend, fps: number): number {
-  if (!(blend.frames > 0) || !(fps > 0)) return 1;
-  return Math.min(1, (blend.elapsed * fps) / blend.frames);
+/** How far a blend has come, 0…1. */
+export function blendShare(blend: AnimationBlend): number {
+  if (!(blend.seconds > 0)) return 1;
+  return Math.min(1, blend.elapsed / blend.seconds);
 }
 
 interface PlayerHolder {
@@ -418,13 +419,13 @@ let startCount = 0;
  * Starts the animation on the object, or lets a paused one run on. One already running keeps its
  * frame, so a graph may ask for it every frame without holding it at its first frame – but it counts
  * as started last again: turning back to a walk that still runs has to show that walk.
- * `blendFrames` crossfades into it – but only when it takes over: asked for again while it already
+ * `blendSeconds` crossfades into it – but only when it takes over: asked for again while it already
  * leads on the object, it keeps the blend it has, so a graph calling every frame does not restart it.
  */
-export function playAnimation(holder: PlayerHolder, animationId: string, blendFrames = 0): void {
+export function playAnimation(holder: PlayerHolder, animationId: string, blendSeconds = 0): void {
   const players = (holder.animations ??= []);
   const known = players.find((p) => p.animationId === animationId);
-  const blend = blendFrames > 0 ? { frames: blendFrames, elapsed: 0 } : undefined;
+  const blend = blendSeconds > 0 ? { seconds: blendSeconds, elapsed: 0 } : undefined;
   if (known) {
     const leads = players.every((p) => p.order <= known.order);
     known.playing = true;