Phase 5 slice B — Animation blend preview + bake-to-clip

[fernandotonon]

Overview

Second slice of #260. Live blend two skeletal animations on the active entity with an adjustable weight, then bake the blended result into a new clip.

Slice A (#356) shipped speed scaling + per-entity loop region; this slice builds on that foundation.

Scope

• New singleton AnimationBlender (or extension of AnimationControlController) that holds:
  • animA, animB — names of the two animations on the active entity
  • weight — 0..1
  • mode — mix (default), additive, override
  • live state controlled per-frame in MainWindow::frameRenderingQueued
• Mix: stateA->setWeight(1 - w), stateB->setWeight(w), both enabled.
• Additive: Skeleton::setBlendMode(ANIMBLEND_CUMULATIVE) on the active entity for the duration of the preview.
• Override: simple A/B selection — only one state enabled, no blend curve (useful for quick swap previews).
• Bake: sample the blended state at a fixed dt (default 30 fps), capture each bone's derived position/orientation/scale after _notifyDirty()+update(), write a new Animation track to the entity's skeleton named Blended_<animA>_<animB> (or user-supplied). Reuse AnimationMerger write helpers where possible.

QML

Inline in the Animations section of PropertiesPanel.qml (next to Play/Speed):

• Two animation pickers (filtered to the active entity's clips)
• Weight slider 0..1
• Mode dropdown (Mix / Additive / Override)
• "Bake to new clip" button + optional clip-name input

Tests

Pure-data fixture (no Ogre):

• weight=0 ⇒ pure A
• weight=1 ⇒ pure B
• weight=0.5 ⇒ midpoint of a synthesized position track

Ogre fixture (Linux CI):

• After bake, the new animation exists on the skeleton with the expected length and keyframe count
• Sampling the new animation at midpoint matches the live blend output

Out of scope

• Blend trees / state machines (multi-state graphs).
• Cross-entity blending — restricted to the active entity's own skeleton.
• More than two animations at once. (Plan defers N-way.)

Acceptance criteria

• Pick two animations on a rigged entity → weight slider visibly mixes them in the viewport
• Toggle Mode → Mix / Additive / Override behave as documented
• Click Bake → new clip appears in the Animations list and plays back identically to the live preview at the same weight
• Speed scaling (slice A) still works while blend preview is active
• Loop region (slice A) still scopes to the selected animation, not the blended pair