Dataflow Arrows

Dashed-line flows show direction via dash offset, but the cue is subtle and can be ambiguous — especially when flows cross or at certain camera angles. Directional arrows make flow direction immediately obvious. This cycle compared rendering approaches to find the best balance of clarity, performance, and fit with the existing line style.

Prototype arrow strategies on a bezier flow curve in a standalone Three.js harness, then productionize the winners as opt-in decorators on LineFlow with full config-schema tuning.

• 2026-04-16 — Landed in the c18-c22 batch commit (work recorded as starting 2026-03-30):
  • Four experimental strategies in dev/experiments/c20.dataflow-arrows/strategies/: ConeArrows (one draw call per cone), InstancedConeArrows (single draw call — performance winner), SpriteArrows (camera-facing, always readable), SlidingArrow (single cone with comet trail — promoted to ArrowIndicator sliding mode)
  • src/flows/ArrowIndicator.js — cone-mesh directional arrows as a decorator on LineFlow; distributed and sliding modes; tangent-aligned via quaternion rotation
  • src/flows/PulseIndicator.js — gradient pulse sweep via TubeGeometry + custom ShaderMaterial (fract(uPulse - vT) moving band, multi-pulse support)
  • LineFlow integration — both decorators opt-in, wired into update/rebuild/setState/dispose; arrow color syncs with flow state; live setters for speed/opacity
  • Config schema expansion in qmapConfigSchema.js — full line/arrow/pulse control set, plus the visibleWhen field so the Configurator hides sub-controls when a parent toggle is off
  • QMap props (showArrows, showPulse, showLine, line dash/opacity settings) with live watchers and a re-apply pattern for highlighted dataflows

Two production-ready decorators (ArrowIndicator + PulseIndicator) integrated into LineFlow and absorbed into the dataflow config schema, tunable via DevConfigurator. The decorator lifecycle (attach, rebuild, update, dispose) proved easy to extend. c21 consolidated this further: LineFlow gained applyConfig() and became fully self-managing, with indicators created exclusively through it and QMap's per-property flow watchers removed.