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BIFOCAL_IMPLEMENTATION_SUMMARY.md

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Bifocal Display Implementation Summary

Completed Implementation

The bifocal display system has been successfully implemented as the default navigation mechanism for the TimeArcs visualization. It is always enabled and starts with a full overview, allowing users to directly manipulate the timeline via drag handles.

Files Created

1. src/scales/bifocal.js (~250 LOC)

Core transform module with:

  • bifocalTransform() - Maps normalized time [0,1] to screen position [0,1]
  • bifocalInverse() - Inverse transform for click-to-time conversion
  • computeLayoutWidths() - Calculates region widths from compression ratio
  • updateFocusRegion() - Updates focus with clamping and validation
  • createBifocalXScale() - Compatible with xScaleLens interface

2. src/ui/bifocal-handles.js (~225 LOC)

SVG drag handles module with:

  • Focus region rectangle (draggable to move)
  • Left/right resize handles (drag to adjust boundaries)
  • Boundary indicator lines (visual guides)
  • D3 drag behaviors with proper clamping

Files Modified

3. src/scales/distortion.js

  • Added import { bifocalTransform } from './bifocal.js'
  • Modified createLensXScale() to check bifocal first (priority 1)
  • Bifocal > Fisheye > Legacy Lens (in priority order)

4. attack_timearcs.html

Added UI controls:

  • Bifocal Toggle Button - #bifocalToggle (Shift+B shortcut)
  • Compression Slider - #compressionSlider (1-10x range)
  • Region Indicator - #bifocalRegionIndicator (shows focus bounds)

5. attack_timearcs.js (~150 LOC added)

Major changes:

  • State Variables (lines 320-328): Added bifocalEnabled, bifocalState, bifocalHandles
  • DOM References (lines 42-46): Added bifocal control element references
  • Imports (lines 12-13): Added bifocal and handles imports
  • Event Handlers (lines 192-263):
    • Compression slider handler
    • Bifocal toggle button handler
    • Button state management functions
    • Keyboard shortcuts (Shift+B, Arrow keys)
  • Scale Creation (lines 1205-1206): Added bifocal getters to createLensXScale()
  • Visualization Update (lines 3622-3715): Created updateBifocalVisualization()
  • Handles Creation (lines 3717-3728): Initialize bifocal drag handles

Features Implemented

Core Functionality

✅ Three-region timeline (left context, focus, right context) ✅ Sharp transitions (no smooth distortion like fisheye) ✅ Monotonicity preservation (temporal ordering maintained) ✅ Compression ratio control (1-10x via slider)

UI Interactions

✅ Always-on by default - starts with full overview (focus = entire timeline) ✅ Draggable focus region (move entire region left/right) ✅ Resize handles (adjust left/right boundaries independently) ✅ Keyboard navigation:

  • Arrow Left/Right: Move focus region (Shift for large steps)
  • Arrow Up/Down: Expand/contract focus region ✅ Visual indicators (boundary lines, region percentage display) ✅ Compression slider for adjusting context detail (1-10x)

Integration

✅ Compatible with existing xScaleLens interface ✅ Mutual exclusion with fisheye (only one active at a time) ✅ Transitions all visual elements smoothly (250ms) ✅ Updates arcs, rows, labels, gradients, and axis ticks

Usage

Overview

Bifocal display is always active - no toggle required. The timeline starts in full overview mode (focus = entire timeline). Simply drag handles to zoom into areas of interest.

Adjust Focus Region

  • Drag center: Move entire focus region
  • Drag left handle: Adjust left boundary
  • Drag right handle: Adjust right boundary
  • Arrow Left/Right: Move region (keyboard)
  • Arrow Up/Down: Expand/contract region (keyboard)

Visual Feedback

  • Blue dashed rectangle shows focus region
  • Vertical dashed lines show boundaries
  • Indicator displays focus percentage (e.g., "Focus: 35% - 65%")

Testing Checklist

Basic Rendering

  • Arcs render correctly in all three regions
  • Row lines span correctly across regions
  • Gradients update at region boundaries
  • Time axis ticks positioned correctly

Drag Interactions

  • Left handle resizes from left
  • Right handle resizes from right
  • Center region moves left/right
  • Minimum focus width enforced (5%)
  • Handles don't cross boundaries

Keyboard Navigation

  • Shift+B toggles bifocal mode
  • Arrow keys move/resize focus
  • Shift modifier increases step size

Integration

  • Fisheye disabled when bifocal enabled
  • Bifocal disabled when fisheye enabled
  • Compression slider updates visualization
  • Smooth transitions (250ms)

Benefits Over Fisheye

  1. Always Available: No mode switching - direct manipulation from the start
  2. Starts with Overview: Full timeline visible initially, zoom in as needed
  3. Predictable: Sharp transitions, no continuous position shifting
  4. Readable Context: Compressed but not distorted
  5. Better for Comparison: Clear focus region boundaries
  6. Intuitive Control: Drag handles vs. mode toggle + mouse tracking
  7. Keyboard Navigation: Arrow keys for precise adjustment
  8. Progressive Disclosure: Handles show interaction is available

Next Steps (Optional)

  • Remove fisheye code after bifocal is validated
  • Add preset focus positions (e.g., "Attack Event 1", "Attack Event 2")
  • Integrate with ground truth events (auto-focus on attack times)
  • Add focus region bookmarks/history
  • Sync with other views (if multi-view layout is added)