Gesture system

SootSim implements the React Native responder system and integrates with react-native-gesture-handler.

Responder system

The touch pipeline (engine/touch/):

1. Hit testing — find the deepest node at touch coordinates
2. Responder negotiation — walk up the tree asking onStartShouldSetResponder
3. Event dispatch — send touchStart/touchMove/touchEnd to the responder
4. Responder transfer — handle onMoveShouldSetResponder for mid-gesture transfers

Hit testing

engine/hit-test.ts walks the node tree depth-first, checking if the touch point falls within each node’s absolute bounds. Respects:

• pointerEvents (none, box-none, box-only, auto)
• overflow: hidden clipping
• z-index ordering

Gesture handler integration

The react-native-gesture-handler stub (@soot/compat) provides:

• Tap — single and double tap with position tracking
• Pan — translation, velocity, state machine
• LongPress — duration-based with position
• Composed gestures — Race, Simultaneous, Exclusive

Gesture support is implemented inside the engine’s touch, hit-test, scroll, and gesture-handler layers so responder ownership and gesture state are derived from the same live render tree the app is running against.

Scroll

engine/scroll.ts implements iOS scroll physics:

• Deceleration — momentum after release
• Rubber band — elastic overscroll at bounds
• Snap — pagingEnabled snapping
• Indicators — auto-hiding scroll bars