Phase 4 — Interactive Gating

[hypercompetent]

Part of the PyQt → Dash/Plotly migration. See cytoflowweb/PLAN.md for full context.

Estimated effort: 2–3 weeks
Depends on: Phase 2 (#2), Phase 3 (#3)

Tasks

• Threshold gate: dcc.Graph clickData callback → updates numeric input; vertical line rendered as go.layout.Shape
• Range gate: dcc.RangeSlider below the plot, or Plotly dragmode='select' + selectedData.range.x
• 2D range / quad gates: Plotly dragmode='select' → box-select → selectedData.range
• Lasso gate: Plotly dragmode='lasso' → selectedData.lassoPoints → inverse-scale transform → PolygonOp vertices
• Gate overlay rendering: committed gate drawn as a closed go.layout.Shape path overlaid on the plot

Gate mechanism summary

Gate type	Plotly/Dash mechanism
Threshold	clickData → go.layout.Shape vertical line
Range (1D)	dcc.RangeSlider or dragmode='select' + selectedData.range.x
Rectangle / Quad (2D)	dragmode='select' → selectedData.range
Non-rectangular (replaces PolygonOp)	dragmode='lasso' → selectedData.lassoPoints.{x,y}

Notes

• Lasso coordinates arrive in pre-transformed (scale) space. Apply scale.inverse() before passing vertices to PolygonOp — the op itself is unchanged.
• Gate overlays rendered as go.layout.Shape objects sit on top of the plot data.
• An optional "refine gate" editable vertex table can be added as a follow-on enhancement.

Milestone

All gate types work end-to-end. Lasso gate commits on mouseup and triggers pipeline re-run downstream.