bug: mouse drag selection and double-click word select don't work in TextField

[kolkov]

Problem

Mouse drag selection and double-click word selection don't work in TextField, despite the selection model being fully implemented internally. The selection model (core/textfield/selection.go), rendering (all 4 theme painters), and keyboard selection (Shift+arrows, Ctrl+A) all work correctly. The gap is in the event dispatch layer.

What works: click to place cursor, Shift+arrows, Ctrl+Shift+arrows (word), Ctrl+A, typing, horizontal scroll.

What doesn't work: mouse drag to select, double-click to select word, Ctrl+C/V to OS clipboard.

Root Cause

Gap 1: MouseDrag never synthesized

app/event_bridge.go:34-38 — OnMouseMove always emits event.MouseMove, even when buttons are pressed. TextField's handleMouseDrag (core/textfield/event.go:49-50) listens for event.MouseDrag which is never dispatched.

Fix: In event_bridge.go, check pressedButtons != 0 during mouse move → emit MouseDrag instead of MouseMove. ~3 lines.

Gap 2: MouseDoubleClick never dispatched

event.MouseDoubleClick type exists (event/mouse.go:33-34). TextField handles it (event.go:52-53, handleDoubleClick selects word via wordBoundsAt()). But no component in the stack generates this event — no double-click timing detector exists in the event bridge, window, or platform layer.

Fix: Add click timing detector in event_bridge.go or app/window.go — two presses within ~400ms at similar position → MouseDoubleClick. Flutter: 300ms, Win32: 500ms. ~30 lines.

Gap 3: Clipboard is internal only

selection.go:9 — clipboard string is an in-memory field. copyToClipboard/pasteFromClipboard (lines 141-151) don't reach the OS clipboard. Ctrl+C/V work within the same widget instance only.

Fix: Wire to platform clipboard — gpucontext.ClipboardProvider interface or direct platform calls (Win32 SetClipboardData/GetClipboardText, macOS NSPasteboard, X11 XSetSelectionOwner, Wayland wl_data_source).

Enterprise References

Feature	Flutter	GTK4	Win32
Drag selection	TextSelectionGestureDetector	gtk_text_handle_drag	WM_MOUSEMOVE + MK_LBUTTON
Double-click	kDoubleTapTimeout = 300ms	GDK_2BUTTON_PRESS	WM_LBUTTONDBLCLK (500ms default)
Triple-click	kDoubleTapTimeout chain	GDK_3BUTTON_PRESS	Manual detection
OS clipboard	Clipboard.getData	gtk_clipboard_get	GetClipboardData

Implementation Priority

1. MouseDrag synthesis (~3 LOC) — unblocks drag selection immediately
2. Double-click detection (~30 LOC) — word selection
3. OS clipboard (~100 LOC across platforms) — copy/paste interop
4. Triple-click line select (~10 LOC) — nice-to-have

[kolkov]

Investigation complete. The three gaps identified in this issue are symptoms of a deeper architectural need: gogpu/ui has no unified gesture recognition system. Each of our 24 interactive widgets implements ad-hoc gesture logic (click counting, drag tracking, threshold detection) independently.

Architecture Decision

ADR-049: Gesture Recognition System — a full Flutter-inspired gesture architecture adapted for Go 2026+, validated against Flutter, Chromium, GTK4, and Qt6 source code.

Key design:

• GestureArena (Flutter pattern) — competing recognizers disambiguate via "first to accept or last to not reject" protocol. Required for both desktop (tap vs drag on Slider) and touch (Android multi-pointer).
• Per-device thresholds — mouse slop 4px (Chromium/Win32), touch slop 18px (Flutter/Android). Same recognizer code, different parameters.
• TapAndDragRecognizer — the TextField solution. Provides consecutiveTapCount on ALL callbacks (tap and drag). Double-tap-drag = word-by-word selection, triple-tap-drag = line-by-line. Exactly how Flutter's TextSelectionGestureDetector works.
• Reactive signals (coregx/signals) — gesture state (IsDragging, DragPosition) exposed as opt-in Signal[T] via functional options. Integrates with existing BindToScheduler pattern.
• Event bridge migration — switch from legacy OnMouseMove/Press/Release to consuming gpucontext.PointerEvent directly. The rich W3C data (PointerID, PointerType, Pressure, Timestamp) is already provided by all platform backends but currently discarded by the bridge.

Implementation Plan

Phase	Scope	LOC	Status
1	gesture/ package: Arena, Click, Drag, LongPress, TapAndDrag recognizers, VelocityTracker	~2,970	In progress
2	Event bridge PointerEvent migration + Window arena integration	~800	Next
3	Widget migration: TextField first (#225), then Button, Slider, ScrollView, etc.	~1,200	Next
4	ScaleRecognizer (pinch/zoom/rotate) for Android multi-touch	~700	Backlog

TextField drag selection, double-click word select, and triple-click line select will be available after Phase 3 widget migration. OS clipboard (Gap 3) is tracked separately.