Pad/internal/ui/render.go

package ui

import (
	"bytes"
	"embed"
	"image"
	"image/color"
	_ "image/png"
	"sort"
	"time"
	"unicode/utf8"

	"gioui.org/f32"
	"gioui.org/gesture"
	"gioui.org/io/event" // Import event package
	"gioui.org/io/input"
	"gioui.org/io/key"
	"gioui.org/io/pointer"
	"gioui.org/layout"
	"gioui.org/op"
	"gioui.org/op/clip"
	"gioui.org/op/paint"
	"gioui.org/text"
	"gioui.org/unit"
	"gioui.org/widget"
	"golang.org/x/image/math/fixed"
)

// maxInt32 is a large value used as MaxWidth for single-line text layout.
const maxInt32 = 1<<31 - 1

//go:embed icons/*.png
var iconFS embed.FS

// clickReg pairs a gesture.Click with its handler.
type clickReg struct {
	click   *gesture.Click
	handler func(any)
	// pressAt/pressPos record the current press (set on KindPress) so the
	// per-frame long-press check knows how long the finger has been still.
	pressAt   time.Time
	pressPos  image.Point
	longFired bool
}

// longPressDuration is how long a still press must hold before a long-press
// fires (Android uses ~500ms; 400ms feels snappier for text selection).
const longPressDuration = 400 * time.Millisecond

// longPressSlopPx is how far the finger may drift (px) before a pending
// long press is cancelled (that motion becomes a scroll/drag instead).
const longPressSlopPx = 8

// keyReg pairs a handler for key events.
type keyReg struct {
	Handler func(any)
}

// scrollReg pairs a gesture.Scroll with its handler.
type scrollReg struct {
	scroll  *gesture.Scroll
	handler func(any)
}

// Renderer consumes a slice of elements and draws them.
//
// The Renderer is owned by the main goroutine. It is the home of any state
// that Gio mutates during draw (e.g. the search bar's widget.Editor): such
// state must not live in the logic goroutine's State (architecture.md §1).
type Renderer struct {
	theme            Theme
	shp              *text.Shaper
	scale            float32 // px-per-Dp for the current draw pass; set in Draw
	icons            map[string]image.Image
	clicks           map[string]*clickReg
	Keys             map[string]keyReg // Exported Keys map
	scrolls          map[string]scrollReg
	gioEditors       map[string]*widget.Editor // main-owned widget editors by element ID
	displayLineCount int                       // number of display lines from last drawWrappedText
	lastLineY        Dp                        // last line baseline offset from text origin, in Dp (derived from GlyphLayout)
	glyphLayout      GlyphLayout               // captured per-glyph layout from last drawWrappedText

	// IME dedup (main-owned, persistent across frames). Re-pushing an unchanged
	// snippet or selection every frame resets the IME's composition and caret,
	// which desyncs fast commits; push only on change, as widget.Editor does in
	// updateSnippet and its selection gating. Keyed to the focused field's ID so
	// it stays correct if a second TextField is ever added.
	lastIMEField   string
	lastWasFocused bool
	lastSnippet    key.Snippet
	lastSelStart   int    // window-relative rune index of last-pushed selection start; -1 = no selection
	lastSelCaret   int    // window-relative rune index of last-pushed selection end/caret
	lastIMEShowSeq uint64 // last ShowIMESeq value that issued SoftKeyboardCmd{Show:true}

	// FocusCmd dedup (main-owned, persistent across frames). key.FocusCmd is
	// issued ONLY on a focus transition, never per frame: even a no-op FocusCmd
	// (same focus) takes the router's "immediate command" path, which re-queues
	// the frame's pending pointer events and re-delivers every touch event to
	// every gesture. During a selection-handle drag that replayed each event
	// several times per frame, making the selection unusable. The key queue
	// keeps the focus until the handler stops registering as focusable, so one
	// command per transition is sufficient.
	lastFocusCmdID string
	// focusSeenThisFrame is reset at the start of each Draw; if no focused
	// TextField was drawn in the frame, lastFocusCmdID is cleared so a field
	// regaining focus later re-issues the command.
	focusSeenThisFrame bool

	// Long-press detection. pressProbe is a plain event tag observing raw
	// pointer events inside the editor text region: gesture.Click reports
	// nothing until release, so a long press (finger held still for
	// longPressDuration) can only be detected this way. ppMoved cancels the
	// pending long press once the finger leaves longPressSlopPx (it is a
	// scroll/drag then, not a press). longPressID gates the long-press to the
	// editor's click reg (browser rows etc. don't long-press). ppLast is in
	// f32.Point because pointer.Event.Position is window-space f32.
	pressProbe  struct{}
	ppLast      f32.Point
	ppActive    bool
	ppMoved     bool
	longPressID string

	// Selection / caret drag handles (0 = start, 1 = end, 2 = body, 3 = caret
	// handle). Registered clipped in drawWrappedText only while a selection or
	// caret handle is visible; a gesture.Drag grabs the pointer once movement
	// exceeds slop, which cancels the scroll and click handlers so a handle
	// drag never fights a fling. selDragEmitting tracks whether a Drag event
	// was delivered for the current gesture (so a plain tap on a handle does
	// not emit a spurious SelectionDragEnd).
	selDragStart    gesture.Drag
	selDragEnd      gesture.Drag
	selDragBody     gesture.Drag
	selDragCaret    gesture.Drag
	selDragsOn      [4]bool
	selDragEmitting [4]bool
	selDragHandler  func(any)
	// selDraggingWhich is which handle drag (0-3) is currently in flight
	// (-1 = none), set by CheckGestures and read by drawWrappedText to
	// enlarge the grabbed handle, as the framework does while dragging.
	selDraggingWhich int
	// selDragActive reports that a selection/caret drag is in progress.
	// TextField.Draw skips the key.SelectionCmd IME sync while it is set:
	// the command triggers the router's immediate-command path, which
	// re-queues the frame's pointer events and replays every drag event
	// into the gestures (a replay storm — each re-queued event lands in
	// q.changes and is re-queued again on the next SelectionCmd). The IME
	// only needs the final selection, pushed on the first frame after the
	// drag ends.
	selDragActive bool
	// gestureExclusions holds the selection-handle grab boxes (view-local
	// px, [x0, y0, x1, y1]) collected by drawWrappedText for the current
	// frame. On Android the main loop forwards them to
	// View.setSystemGestureExclusionRects (API 29+) so drags starting on an
	// edge handle are not stolen by the system back gesture.
	gestureExclusions [][4]int
}

// GestureExclusions returns the handle grab boxes collected for the last
// frame (see gestureExclusions).
func (r *Renderer) GestureExclusions() [][4]int { return r.gestureExclusions }

// pointInHandleBox reports whether the window-pixel point lies inside one of
// the last frame's selection/caret handle grab boxes (gestureExclusions holds
// those boxes, clipped to the editor region).
func (r *Renderer) pointInHandleBox(p image.Point) bool {
	for _, b := range r.gestureExclusions {
		// Boxes are [x0, y0, x1, y1].
		if p.X >= b[0] && p.X < b[2] && p.Y >= b[1] && p.Y < b[3] {
			return true
		}
	}
	return false
}

// New creates a new Renderer.
func New(th Theme, shp *text.Shaper) *Renderer {
	r := &Renderer{
		theme:            th,
		shp:              shp,
		icons:            make(map[string]image.Image),
		clicks:           make(map[string]*clickReg),
		Keys:             make(map[string]keyReg),
		scrolls:          make(map[string]scrollReg),
		gioEditors:       make(map[string]*widget.Editor),
		selDraggingWhich: -1,
	}
	r.loadIcons()
	return r
}

// RegisterGioEditor attaches a main-owned widget.Editor to an element ID.
// GioEditor elements with that ID render the widget during draw. Must be
// called from the main goroutine before the first frame.
func (r *Renderer) RegisterGioEditor(id string, ed *widget.Editor) {
	r.gioEditors[id] = ed
}

// GioEditor returns the main-owned widget editor registered for id, if any.
func (r *Renderer) GioEditor(id string) (*widget.Editor, bool) {
	ed, ok := r.gioEditors[id]
	return ed, ok
}

// loadIcons loads PNG icons from the embedded filesystem.
func (r *Renderer) loadIcons() {
	for _, name := range []string{"back", "cut", "copy", "paste", "search", "close", "chevron_up", "chevron_down"} {
		data, err := iconFS.ReadFile("icons/" + name + ".png")
		if err != nil {
			continue
		}
		img, _, err := image.Decode(bytes.NewReader(data))
		if err != nil {
			continue
		}
		r.icons[name] = img
	}
}

// icon returns a loaded icon image by name, or nil if not found.
func (r *Renderer) icon(name string) image.Image {
	return r.icons[name]
}

// toPx converts Dp to physical pixels using State's scale.
func (r *Renderer) toPx(dp Dp) Px {
	return ToPx(dp, r.scale)
}

// toDp converts physical pixels to Dp using State's scale.
func (r *Renderer) toDp(px Px) Dp {
	return ToDp(px, r.scale)
}

// Draw iterates elements and draws each in slice order (back-to-front).
// Draw renders the given elements. scale is the px-per-Dp factor for this
// draw pass, taken from the frame's view-state snapshot (the renderer never
// reads logic state directly).
func (r *Renderer) Draw(gtx layout.Context, elems []Element, scale float32) {
	r.scale = scale
	r.focusSeenThisFrame = false // per-frame reset for FocusCmd dedup
	// Gio sets constraints to layout.Exact(windowSize), so Min==Max. Use (0,0) as Min.
	winW := gtx.Constraints.Max.X
	winH := gtx.Constraints.Max.Y
	clipRect := clip.Rect{
		Min: image.Point{X: 0, Y: 0},
		Max: image.Point{X: winW, Y: winH},
	}.Push(gtx.Ops)

	for _, e := range elems {
		if !e.Visible() {
			continue
		}
		r.drawElement(gtx, e)
	}

	// If no focused TextField was drawn this frame, the key queue will drop
	// the focus (the focused handler stops registering as focusable). Clear the
	// dedup so the same field re-issues key.FocusCmd when it regains focus.
	if !r.focusSeenThisFrame {
		r.lastFocusCmdID = ""
	}

	clipRect.Pop()
}

// registerInteraction registers a gesture for an element.
// Supports Tap and Scroll.
// The clip context must already be set to the element's bounds before calling this.
func (r *Renderer) registerInteraction(id string, interaction Interaction, gtx layout.Context) {
	switch interaction.Gesture {
	case Tap:
		reg, ok := r.clicks[id]
		if !ok {
			reg = &clickReg{click: &gesture.Click{}}
			r.clicks[id] = reg
		}
		reg.handler = interaction.Handler
		// Register click within current clip context
		reg.click.Add(gtx.Ops)
	case Scroll:
		reg, ok := r.scrolls[id]
		if !ok {
			reg = scrollReg{scroll: &gesture.Scroll{}}
		}
		// Register scroll within current clip context
		reg.scroll.Add(gtx.Ops)
		reg.handler = interaction.Handler
		r.scrolls[id] = reg
	case SelDrag:
		// The renderer registers the actual gesture.Drag ops in
		// drawWrappedText (it owns the handle geometry); this only records the
		// logic handler that receives the drag events.
		r.selDragHandler = interaction.Handler
	}
}

// RegisterClick registers a click gesture for a rectangular region.
// Used by ListView to register per-row click areas. The click.Add() call
// is made within a clip so only the region is clickable.
func (r *Renderer) RegisterClick(gtx layout.Context, id string, region Region, handler func(any)) {
	reg, ok := r.clicks[id]
	if !ok {
		reg = &clickReg{click: &gesture.Click{}}
		r.clicks[id] = reg
	}
	reg.handler = handler
	// Clip to the specified region for click area
	clickClip := clip.Rect{
		Min: image.Point{X: int(r.toPx(region.X)), Y: int(r.toPx(region.Y))},
		Max: image.Point{X: int(r.toPx(region.X + region.W)), Y: int(r.toPx(region.Y + region.H))},
	}.Push(gtx.Ops)
	reg.click.Add(gtx.Ops)
	clickClip.Pop()
}

// RegisterScroll registers a scroll gesture for a rectangular region.
// Should be called while the element's clip is active (e.g., inside a container
// or clippable element's Draw method).
func (r *Renderer) RegisterScroll(gtx layout.Context, id string, region Region, handler func(any)) {
	reg, ok := r.scrolls[id]
	if !ok {
		reg = scrollReg{scroll: &gesture.Scroll{}}
	}
	reg.handler = handler
	r.scrolls[id] = reg
	reg.scroll.Add(gtx.Ops)
}

// PendingLongPress reports whether a press is currently held still on the
// editor (long-press armed but not yet fired). Gio renders on demand: with a
// stationary finger there are no pointer events, hence no frames, and the
// 400 ms threshold could never be checked. The main loop calls this and
// invalidates the window while it is true, keeping frames flowing until the
// long press fires or the finger moves up.
func (r *Renderer) PendingLongPress() bool {
	reg, ok := r.clicks[r.longPressID]
	return ok && reg.click.Pressed() && !reg.longFired && !r.ppMoved && !reg.pressAt.IsZero()
}

// CheckGestures checks all registered gestures and returns any events.
func (r *Renderer) CheckGestures(q input.Source, m unit.Metric) []InputEvent {
	var events []InputEvent
	// Long-press motion probe first: it must see the press/drag events before
	// the click loop decides about a long press.
	r.consumePressProbe(q)
	for id, reg := range r.clicks {
		// Drain every queued event for this gesture in this frame.
		// gesture.Click returns one event per Update call, but on Android a
		// tap's press and release routinely arrive in the same frame. Without
		// draining, the release would sit unprocessed until the next redraw —
		// which on an idle window may never come — and the tap is swallowed.
		for {
			evt, ok := reg.click.Update(q)
			if !ok {
				break
			}
			switch evt.Kind {
			case gesture.KindPress:
				reg.pressAt = time.Now()
				reg.pressPos = evt.Position
				reg.longFired = false
			case gesture.KindClick:
				if reg.longFired {
					break // the press was consumed as a long press
				}
				if r.pointInHandleBox(evt.Position) {
					// A tap inside a handle grab box is a handle touch that
					// never reached the drag slop (or a deliberate light
					// touch on the handle): it must be a no-op, not a text
					// tap. Forwarding it would clear the selection and move
					// the caret, so a light touch on a handle destroyed the
					// selection. (Native Android: tapping a handle does
					// nothing.)
					break
				}
				if evt.NumClicks >= 2 {
					events = append(events, InputEvent{
						Handler: reg.handler,
						Data:    DoubleTapPoint{X: r.toDp(Px(evt.Position.X)), Y: r.toDp(Px(evt.Position.Y))},
					})
				} else {
					events = append(events, InputEvent{
						Handler: reg.handler,
						Data:    Point{X: r.toDp(Px(evt.Position.X)), Y: r.toDp(Px(evt.Position.Y))},
					})
				}
			case gesture.KindCancel:
				reg.pressAt = time.Time{}
				reg.longFired = false
			}
		}
		// Long press: the finger must still be down on the probed (editor)
		// region, held still, for the long-press duration.
		if id == r.longPressID && reg.click.Pressed() && !reg.longFired &&
			!r.ppMoved && !reg.pressAt.IsZero() && time.Since(reg.pressAt) >= longPressDuration {
			reg.longFired = true
			events = append(events, InputEvent{
				Handler: reg.handler,
				Data:    LongPressPoint{X: r.toDp(Px(reg.pressPos.X)), Y: r.toDp(Px(reg.pressPos.Y))},
			})
		}
	}
	// Selection / caret drags before scroll: a handle grab must win over fling.
	drags := [4]*gesture.Drag{&r.selDragStart, &r.selDragEnd, &r.selDragBody, &r.selDragCaret}
	for which, d := range drags {
		if !r.selDragsOn[which] || r.selDragHandler == nil {
			continue
		}
		// wasDragging is captured before Update: Update resets Dragging() on
		// Release/Cancel, so it would read false afterwards.
		wasDragging := d.Dragging()
		// Drain all queued events for this drag in this frame (same
		// one-event-per-Update rationale as the click loop above).
		for {
			e, ok := d.Update(m, q, gesture.Both)
			if !ok {
				break
			}
			switch e.Kind {
			case pointer.Drag:
				// Forward only grabbed events: gesture.Drag also returns the
				// pre-grab (Shared priority) moves, and acting on those would
				// start moving the selection at the press position — the grab
				// jitter. The first Grabbed event lands just past the touch slop,
				// matching native Android, where the handle follows only after
				// the slop.
				if e.Priority != pointer.Grabbed {
					continue
				}
				r.selDragEmitting[which] = true
				r.selDraggingWhich = which
				r.selDragActive = true
				events = append(events, InputEvent{
					Handler: r.selDragHandler,
					Data:    SelectionDragEvent{Which: which, X: r.toDp(Px(e.Position.X)), Y: r.toDp(Px(e.Position.Y))},
				})
			case pointer.Release, pointer.Cancel:
				if wasDragging && r.selDragEmitting[which] {
					events = append(events, InputEvent{
						Handler: r.selDragHandler,
						Data:    SelectionDragEnd{},
					})
				}
				r.selDragEmitting[which] = false
				if r.selDraggingWhich == which {
					r.selDraggingWhich = -1
				}
			}
		}
	}
	// Safety net: if no gesture is still dragging but a selection/caret drag
	// was active (e.g. the release was never delivered), clear the flag so the
	// IME selection sync (key.SelectionCmd) resumes — see TextField.Draw.
	if r.selDragActive {
		stillDragging := false
		for _, d := range drags {
			if d.Dragging() {
				stillDragging = true
				break
			}
		}
		if !stillDragging {
			r.selDragActive = false
		}
	}
	for _, reg := range r.scrolls {
		// gesture.Scroll.Update returns scroll delta in pixels.
		// ScrollY range: Min = -scrollOffset (remaining above), Max = large (content height unknown yet).
		// With Min==Max==0, clampSplit consumes zero scroll.
		delta := reg.scroll.Update(m, q, time.Now(), gesture.Vertical,
			pointer.ScrollRange{}, pointer.ScrollRange{Min: -(1 << 30), Max: 1 << 30})
		if delta != 0 {
			events = append(events, InputEvent{
				Handler: reg.handler,
				Data:    delta,
			})
		}
	}

	return events
}

// consumePressProbe drains the raw pointer events of the long-press probe
// and updates ppLast/ppMoved. It runs before the click loop each frame.
func (r *Renderer) consumePressProbe(q input.Source) {
	for {
		evt, ok := q.Event(pointer.Filter{Target: r.pressProbe, Kinds: pointer.Press | pointer.Drag | pointer.Release | pointer.Cancel})
		if !ok {
			return
		}
		pe, ok := evt.(pointer.Event)
		if !ok {
			continue
		}
		switch pe.Kind {
		case pointer.Press:
			r.ppLast = pe.Position
			r.ppActive = true
			r.ppMoved = false
		case pointer.Drag:
			if r.ppActive {
				dx, dy := pe.Position.X-r.ppLast.X, pe.Position.Y-r.ppLast.Y
				if dx*dx+dy*dy > float32(longPressSlopPx*longPressSlopPx) {
					r.ppMoved = true
				}
			}
			r.ppLast = pe.Position
		case pointer.Release, pointer.Cancel:
			r.ppMoved = false
			r.ppActive = false
		}
	}
}

// DisplayLineCount returns the number of display lines from the last
// drawWrappedText call. Used by the main loop to report back to logic.
func (r *Renderer) DisplayLineCount() int {
	return r.displayLineCount
}

// LastLineY returns the last line baseline offset from the text origin, in Dp.
// Used by logic to compute max scroll without off-by-one errors.
func (r *Renderer) LastLineY() Dp {
	return r.lastLineY
}

// GlyphLayout returns the glyph layout data captured during the last
// drawWrappedText call. Used by the logic goroutine to position the cursor
// and navigate by glyph instead of byte offset.
func (r *Renderer) GlyphLayout() GlyphLayout {
	return r.glyphLayout
}

// clippableElement is implemented by elements that need their own clip region
// around all their content and interaction registrations.
type clippableElement interface {
	NeedsClip() bool
}

func (r *Renderer) drawElement(gtx layout.Context, e Element) {
	reg := e.Region()

	if container, ok := e.(Container); ok {
		// Clip to container bounds, draw background, then offset children
		clipRect := clip.Rect{
			Min: image.Point{X: int(r.toPx(reg.X)), Y: int(r.toPx(reg.Y))},
			Max: image.Point{X: int(r.toPx(reg.X + reg.W)), Y: int(r.toPx(reg.Y + reg.H))},
		}.Push(gtx.Ops)
		e.Draw(gtx, r) // draw container background
		offset := op.Offset(image.Pt(int(r.toPx(reg.X)), int(r.toPx(reg.Y)))).Push(gtx.Ops)
		for _, child := range container.Children {
			r.drawElement(gtx, child)
		}
		offset.Pop()
		clipRect.Pop()
	} else if clippable, ok := e.(clippableElement); ok && clippable.NeedsClip() {
		// Clip to element bounds before registering interactions and drawing.
		// event.Op for key events must be within the clip so Gio routes events
		// to this element's tag.
		clipRect := clip.Rect{
			Min: image.Point{X: int(r.toPx(reg.X)), Y: int(r.toPx(reg.Y))},
			Max: image.Point{X: int(r.toPx(reg.X + reg.W)), Y: int(r.toPx(reg.Y + reg.H))},
		}.Push(gtx.Ops)
		// Register interactions inside the clip so event.Op is scoped to this region.
		if interactive, ok := e.(Interactive); ok {
			for _, interaction := range interactive.Interactions() {
				if interaction.Gesture == KeyDown || interaction.Gesture == KeyUp {
					event.Op(gtx.Ops, interactive.ID())
					reg := keyReg{Handler: interaction.Handler}
					r.Keys[interactive.ID()] = reg
					break
				}
			}
			for _, interaction := range interactive.Interactions() {
				if interaction.Gesture == Scroll {
					reg, ok := r.scrolls[interactive.ID()]
					if !ok {
						reg = scrollReg{scroll: &gesture.Scroll{}}
					}
					reg.scroll.Add(gtx.Ops)
					reg.handler = interaction.Handler
					r.scrolls[interactive.ID()] = reg
				}
				if interaction.Gesture == Tap {
					reg, ok := r.clicks[interactive.ID()]
					if !ok {
						reg = &clickReg{click: &gesture.Click{}}
						r.clicks[interactive.ID()] = reg
					}
					reg.handler = interaction.Handler
					reg.click.Add(gtx.Ops)
				}
				if interaction.Gesture == SelDrag {
					// Store the logic handler; the drag ops themselves are added
					// clipped in drawWrappedText where the handle geometry is known.
					r.registerInteraction(interactive.ID(), interaction, gtx)
				}
			}
		}
		e.Draw(gtx, r)
		clipRect.Pop()
	} else {
		// Leaf element: register click handlers, then draw.
		// For text elements, click registration happens inside Draw after shaping.
		if interactive, ok := e.(Interactive); ok {
			// Register input tag for key events
			for _, interaction := range interactive.Interactions() {
				if interaction.Gesture == KeyDown || interaction.Gesture == KeyUp {
					event.Op(gtx.Ops, interactive.ID())

					// Register handler
					reg := keyReg{Handler: interaction.Handler}
					r.Keys[interactive.ID()] = reg
					break
				}
			}

			for _, interaction := range interactive.Interactions() {
				// Set up click handler (but don't call Add for text elements)
				if interaction.Gesture == Tap {
					reg, ok := r.clicks[interactive.ID()]
					if !ok {
						reg = &clickReg{click: &gesture.Click{}}
						r.clicks[interactive.ID()] = reg
					}
					reg.handler = interaction.Handler
				}
				// For non-text elements, register click immediately
				if _, isLabel := e.(Label); !isLabel {
					elemClip := clip.Rect{
						Min: image.Point{X: int(r.toPx(reg.X)), Y: int(r.toPx(reg.Y))},
						Max: image.Point{X: int(r.toPx(reg.X + reg.W)), Y: int(r.toPx(reg.Y + reg.H))},
					}.Push(gtx.Ops)
					r.registerInteraction(interactive.ID(), interaction, gtx)
					elemClip.Pop()
				}
			}
		}
		e.Draw(gtx, r)
	}
}

func (r *Renderer) drawBg(gtx layout.Context, reg Region, col Color) {
	bgClip := clip.Rect{
		Min: image.Point{X: int(r.toPx(reg.X)), Y: int(r.toPx(reg.Y))},
		Max: image.Point{X: int(r.toPx(reg.X + reg.W)), Y: int(r.toPx(reg.Y + reg.H))},
	}.Push(gtx.Ops)
	paint.ColorOp{Color: color.NRGBA{R: col.R, G: col.G, B: col.B, A: col.A}}.Add(gtx.Ops)
	paint.PaintOp{}.Add(gtx.Ops)
	bgClip.Pop()
}

func (r *Renderer) drawText(gtx layout.Context, str string, size unit.Sp, reg Region, align TextAlign, col Color, id string) {
	if str == "" {
		return
	}
	params := text.Parameters{
		PxPerEm:  fixed.I(gtx.Sp(size)),
		MinWidth: 0,
		MaxWidth: maxInt32,
		MaxLines: 1,
	}

	// Measure text width via glyph iteration (consumes iterator)
	r.shp.LayoutString(params, str)
	var totalAdvance fixed.Int26_6
	for g, ok := r.shp.NextGlyph(); ok; g, ok = r.shp.NextGlyph() {
		totalAdvance += g.Advance
	}
	textW := Dp(float32(totalAdvance>>6) / r.scale)

	// Compute aligned X position
	var drawX Dp
	switch align {
	case AlignStart:
		drawX = reg.X
	case AlignCenter:
		drawX = reg.X + (reg.W-textW)/2
	case AlignEnd:
		drawX = reg.X + reg.W - textW
	}

	// Clip to just the text area
	textClip := clip.Rect{
		Min: image.Point{X: int(r.toPx(drawX)), Y: int(r.toPx(reg.Y))},
		Max: image.Point{X: int(r.toPx(drawX + textW)), Y: int(r.toPx(reg.Y + reg.H))},
	}.Push(gtx.Ops)

	// Register click within the text clip if this is an interactive label
	if id != "" {
		if reg, ok := r.clicks[id]; ok && reg.click != nil {
			reg.click.Add(gtx.Ops)
		}
	}

	// Layout again (iterator consumed) and draw
	r.shp.LayoutString(params, str)
	r.drawLineText(gtx, drawX, reg.Y, col)

	textClip.Pop()
}
func (r *Renderer) drawLineText(gtx layout.Context, x, y Dp, col Color) {
	m := op.Record(gtx.Ops)
	var glyphs [32]text.Glyph
	line := glyphs[:0]
	for g, ok := r.shp.NextGlyph(); ok; g, ok = r.shp.NextGlyph() {
		line = append(line, g)
		if g.Flags&text.FlagLineBreak != 0 || cap(line)-len(line) == 0 {
			r.drawLine(gtx, line, x, y, col)
			line = line[:0]
		}
	}
	if len(line) > 0 {
		r.drawLine(gtx, line, x, y, col)
	}
	call := m.Stop()
	call.Add(gtx.Ops)
}

// drawLine draws a single line of glyphs at the given position.
// Matches Gio's paintGlyph: offset by (x + first.X, y + first.Y).
func (r *Renderer) drawLine(gtx layout.Context, line []text.Glyph, x, y Dp, col Color) {
	if len(line) == 0 {
		return
	}
	first := line[0]
	// Offset: desired document position + first glyph's relative position.
	// first.X is in fixed.Int26_6 (divide by 64 for pixels), first.Y is in pixels.
	offX := float32(gtx.Dp(unit.Dp(x))) + float32(first.X)/64.0
	offY := float32(gtx.Dp(unit.Dp(y))) + float32(first.Y)
	t := op.Affine(f32.Affine2D{}.Offset(f32.Pt(offX, offY))).Push(gtx.Ops)

	// Draw vector glyphs
	path := r.shp.Shape(line)
	outline := clip.Outline{Path: path}.Op().Push(gtx.Ops)
	paint.ColorOp{Color: color.NRGBA{R: col.R, G: col.G, B: col.B, A: col.A}}.Add(gtx.Ops)
	paint.PaintOp{}.Add(gtx.Ops)
	outline.Pop()

	// Draw bitmap glyphs (emoji, etc.)
	if call := r.shp.Bitmaps(line); call != (op.CallOp{}) {
		call.Add(gtx.Ops)
	}

	t.Pop()
}

// drawWrappedText shapes text once with word wrap and draws display lines inline.
// One LayoutString call - no double-shaping. The shaper handles word boundary
// detection via WrapHeuristically. Long words overflow the wrap width.
// Line spacing is fixed: LineHeight = fontSize × LineHeightScale, independent
// of glyph metrics. The shaper's first.Y accounts for line spacing.
func (r *Renderer) drawWrappedText(gtx layout.Context, str string, reg Region, wordWrap bool, wrapWidth Dp, scrollOffset Dp, cursorPos, selStart, selEnd int, caretDrag bool) {
	if str == "" {
		return
	}
	r.gestureExclusions = nil // rebuilt from this frame's handle boxes

	// Fixed line height based on font size, not glyph metrics.
	lineHeightSp := unit.Sp(float32(r.theme.FontSize) * LineHeightScale)
	// User font-size setting (sp per dp). The shaper draws baselines at
	// Sp(...) physical px, so the RENDERED line pitch in density-dp is
	// lineHeightSp × fontScale. Every dp-space value below (line height,
	// ascent) uses the scaled form so caret/handles/highlight follow the
	// drawn glyphs; the logic side tracks the same factor via
	// EffectiveLineHeight (ScaleEvent.FontScale).
	fontScale := float32(1)
	if gtx.Metric.PxPerDp > 0 && gtx.Metric.PxPerSp > 0 {
		fontScale = gtx.Metric.PxPerSp / gtx.Metric.PxPerDp
	}
	ascent := Dp(float32(r.theme.FontSize) * fontScale)
	lineH := Dp(float32(lineHeightSp) * fontScale)
	// Wrap disabled: shape with unlimited width so lines extend past the
	// region (clipped by textClip below) instead of wrapping.
	maxWidthPx := maxInt32
	if wordWrap {
		maxWidthPx = int(r.toPx(wrapWidth))
	}
	params := text.Parameters{
		PxPerEm:         fixed.I(gtx.Sp(r.theme.FontSize)),
		MinWidth:        0,
		MaxWidth:        maxWidthPx,
		MaxLines:        0, // unlimited - wrap at MaxWidth
		LineHeight:      fixed.I(gtx.Sp(lineHeightSp)),
		LineHeightScale: 1.0, // use LineHeight directly, don't scale
		WrapPolicy:      text.WrapHeuristically,
	}
	r.shp.LayoutString(params, str)

	// Clip to TextField region so text doesn't spill into status/bottom bars
	textClip := clip.Rect{
		Min: image.Point{X: int(r.toPx(reg.X)), Y: int(r.toPx(reg.Y))},
		Max: image.Point{X: int(r.toPx(reg.X + reg.W)), Y: int(r.toPx(reg.Y + reg.H))},
	}.Push(gtx.Ops)

	// Y position: region top minus scroll offset.
	// The shaper's first.Y handles line spacing - each line's first.Y is
	// ascent + lineHeight × lineIndex. drawLine adds first.Y to y,
	// so passing the same y for all lines gives correct baseline spacing.
	y := reg.Y - scrollOffset
	col := Color{R: 0, G: 0, B: 0, A: 255} // black text

	// Pass 1: collect glyph lines and per-glyph layout data (no drawing yet),
	// so the selection highlight can be emitted before the text ops and render
	// underneath it.
	var lines [][]text.Glyph
	var glyphs [32]text.Glyph
	line := glyphs[:0]
	lineCount := 0

	// Capture per-glyph layout data for cursor positioning and navigation.
	var layout GlyphLayout
	layout.LineHeight = lineH
	byteOffset := 0
	layout.VisualLineStarts = append(layout.VisualLineStarts, byteOffset)
	flushLine := func() {
		lines = append(lines, append([]text.Glyph(nil), line...))
		line = line[:0]
	}
	for g, ok := r.shp.NextGlyph(); ok; g, ok = r.shp.NextGlyph() {
		// Record layout data for this glyph.
		// g.X is in fixed.Int26_6 — shift >> 6 for device pixels, divide by scale for Dp.
		// g.Y is the baseline in device pixels.
		// The shaper flags the LAST glyph of every visual line with
		// FlagLineBreak. For hard lines that is the zero-width "\n" cluster
		// glyph (and, after a trailing "\n", one more synthetic end-of-text
		// glyph) — not a character, so it is skipped to keep ByteOffsets a 1:1
		// map to bytes. For SOFT-wrapped lines (and a final line without a
		// trailing newline) the flag instead sits on the line's last visible
		// character, which MUST stay in the layout: dropping it would make taps
		// on the right half of that character and selection highlights of it
		// miss. Zero width is the discriminator (a real glyph always advances).
		if g.Flags&text.FlagLineBreak == 0 || g.Advance != 0 {
			layout.ByteOffsets = append(layout.ByteOffsets, byteOffset)
			layout.X = append(layout.X, Dp(float32(g.X>>6)/r.scale))
			layout.Y = append(layout.Y, Dp(float32(g.Y)/r.scale))
			layout.Advance = append(layout.Advance, Dp(float32(g.Advance>>6)/r.scale))
		}

		// Advance byteOffset by g.Runes.
		for i := uint16(0); i < g.Runes; i++ {
			_, sz := utf8.DecodeRuneInString(str[byteOffset:])
			byteOffset += sz
		}

		line = append(line, g)
		if g.Flags&text.FlagLineBreak != 0 || cap(line)-len(line) == 0 {
			flushLine()
			if g.Flags&text.FlagLineBreak != 0 {
				lineCount++
				layout.VisualLineStarts = append(layout.VisualLineStarts, byteOffset)
			}
		}
	}
	if len(line) > 0 {
		flushLine()
		lineCount++
	}

	// Pass 2: selection highlight (translucent blue), one rect per covered
	// glyph, emitted before the text so glyphs draw on top of it.
	if selStart >= 0 && selEnd > selStart {
		for i := range layout.ByteOffsets {
			b0 := layout.ByteOffsets[i]
			b1 := len(str)
			if i+1 < len(layout.ByteOffsets) {
				b1 = layout.ByteOffsets[i+1]
			}
			if b0 >= selEnd || b1 <= selStart {
				continue
			}
			hx := reg.X + layout.X[i]
			hy := reg.Y - scrollOffset + layout.Y[i] - ascent
			hw := layout.Advance[i]
			hh := lineH
			rect := clip.Rect{
				Min: image.Point{X: int(r.toPx(hx)), Y: int(r.toPx(hy))},
				Max: image.Point{X: int(r.toPx(hx + hw)), Y: int(r.toPx(hy + hh))},
			}.Op().Push(gtx.Ops)
			paint.ColorOp{Color: color.NRGBA{R: 0x33, G: 0x99, B: 0xFF, A: 0x59}}.Add(gtx.Ops)
			paint.PaintOp{}.Add(gtx.Ops)
			rect.Pop()
		}
	}

	// Pass 3: the text itself.
	m := op.Record(gtx.Ops)
	for _, ln := range lines {
		r.drawLine(gtx, ln, reg.X, y, col)
	}
	call := m.Stop()
	call.Add(gtx.Ops)

	// caretPoint maps a window-relative byte offset to the insertion
	// point's region-relative (x, y) in Dp, where y is the line's baseline
	// (see CaretPoint).
	caretPoint := func(byteOff int) (x, y Dp) {
		return CaretPoint(layout, str, byteOff, ascent, lineH)
	}

	// Draw the caret only when the cursor's byte is inside the shaped window
	// (window-relative: [0, len(str)]). The window covers the viewport
	// exactly, so an out-of-range cursor is off-screen and its caret must not
	// be drawn; the caller used to clamp it to 0, which made the caret jump
	// onto the top (or, past the end, the bottom) visible line whenever the
	// user scrolled past it. The boundary values are on-screen: 0 is the
	// window's first byte and len(str) is the window's last insertion point.
	if cursorPos >= 0 && cursorPos <= len(str) {
		// Determine cursor position from `layout` and `cursorPos`
		cursorX, cursorY := caretPoint(cursorPos)
		cursorX = reg.X + cursorX
		cursorY = reg.Y - scrollOffset + cursorY - ascent

		// Draw the cursor (thin vertical bar)
		cursorRegion := Region{
			X: cursorX,
			Y: cursorY,
			W: Dp(2),
			H: lineH, // line height (font-scale aware)
		}
		r.drawBg(gtx, cursorRegion, Color{R: 0, G: 0, B: 0, A: 255})
	}

	// Long-press probe and selection/caret drag handles. The probe op and the
	// (clipped) drag registrations live in the text clip so they only respond
	// inside the editor region.
	r.selDragsOn = [4]bool{}
	event.Op(gtx.Ops, r.pressProbe)
	r.longPressID = "editor_text"
	if r.selDragHandler != nil && (selStart >= 0 && selEnd > selStart || caretDrag) {
		// handleAt mirrors the cursor computation above: window-relative byte
		// offset -> screen Dp of the caret insertion point.
		handleAt := func(byteOff int) (x, y Dp) {
			hx, hy := caretPoint(byteOff)
			return reg.X + hx, reg.Y - scrollOffset + hy - ascent
		}
		// The visual handle (drawHandle) is a ~20dp teardrop centred at
		// (hx, hy+lineH+handleRadius); the GRAB region is a 48dp box around
		// that centre — Android's own handles are small but their touch
		// targets are not (framework slop + 48dp minimum touch target), and
		// 16dp was far too small to grab reliably by finger.
		const handleRadius = Dp(10)
		registerDrag := func(d *gesture.Drag, hx, hy Dp) {
			cy := hy + lineH + handleRadius
			const grab = Dp(24) // 48dp box
			minx, miny := int(r.toPx(hx-grab)), int(r.toPx(cy-grab))
			maxx, maxy := int(r.toPx(hx+grab)), int(r.toPx(cy+grab))
			// System-gesture exclusion (Android API 29+): a drag that STARTS
			// inside ~20dp of the screen edge can be taken over by the system
			// back gesture (predictive back) — it cancels the handle drag and
			// navigates the app away. Excluding the grab boxes (clipped to the
			// editor region, which is what is actually grabbable) keeps edge
			// handles, e.g. the left handle of a line-start selection, usable.
			// The main loop forwards these rects to
			// View.setSystemGestureExclusionRects (see SetGestureExclusions).
			ex0, ey0, ex1, ey1 := minx, miny, maxx, maxy
			if ex0 < int(r.toPx(reg.X)) {
				ex0 = int(r.toPx(reg.X))
			}
			if ey0 < int(r.toPx(reg.Y)) {
				ey0 = int(r.toPx(reg.Y))
			}
			if ex1 > int(r.toPx(reg.X+reg.W)) {
				ex1 = int(r.toPx(reg.X + reg.W))
			}
			if ey1 > int(r.toPx(reg.Y+reg.H)) {
				ey1 = int(r.toPx(reg.Y + reg.H))
			}
			if ex1 > ex0 && ey1 > ey0 {
				r.gestureExclusions = append(r.gestureExclusions, [4]int{ex0, ey0, ex1, ey1})
			}
			hc := clip.Rect{
				Min: image.Point{X: minx, Y: miny},
				Max: image.Point{X: maxx, Y: maxy},
			}.Push(gtx.Ops)
			d.Add(gtx.Ops)
			hc.Pop()
		}
		if selStart >= 0 && selEnd > selStart {
			sx, sy := handleAt(selStart)
			ex, ey := handleAt(selEnd)
			// Body FIRST, handles after: Gio routes a touch to the TOPMOST op
			// whose clip contains the point, and a drag only grabs after it
			// received the PRESS. The handle boxes reach up into the text line
			// (their centres hang below the line) and the body box spans the
			// line, so wherever they overlap the later-registered op wins. The
			// handles are the more specific target and must win the overlap;
			// registering the body last made line-start handles effectively
			// ungrabbable (the body ate the presses).
			// Body: bounding box of the selected glyphs (only for 2+ glyphs; a
			// single-glyph selection is already covered by its two handles).
			var bx0, by0, bx1, by1 Dp
			hasGlyph := false
			for i := range layout.ByteOffsets {
				b0 := layout.ByteOffsets[i]
				b1 := len(str)
				if i+1 < len(layout.ByteOffsets) {
					b1 = layout.ByteOffsets[i+1]
				}
				if b0 >= selEnd || b1 <= selStart {
					continue
				}
				gx := reg.X + layout.X[i]
				gy := reg.Y - scrollOffset + layout.Y[i] - ascent
				gw := layout.Advance[i]
				gh := lineH
				if !hasGlyph {
					bx0, by0, bx1, by1 = gx, gy, gx+gw, gy+gh
					hasGlyph = true
				} else {
					if gx < bx0 {
						bx0 = gx
					}
					if gy < by0 {
						by0 = gy
					}
					if gx+gw > bx1 {
						bx1 = gx + gw
					}
					if gy+gh > by1 {
						by1 = gy + gh
					}
				}
			}
			if hasGlyph {
				bc := clip.Rect{
					Min: image.Point{X: int(r.toPx(bx0)), Y: int(r.toPx(by0))},
					Max: image.Point{X: int(r.toPx(bx1)), Y: int(r.toPx(by1))},
				}.Push(gtx.Ops)
				r.selDragBody.Add(gtx.Ops)
				bc.Pop()
				r.selDragsOn[2] = true
			}
			registerDrag(&r.selDragStart, sx, sy)
			r.selDragsOn[0] = true
			registerDrag(&r.selDragEnd, ex, ey)
			r.selDragsOn[1] = true
			r.drawHandle(gtx, sx, sy, lineH, r.selDraggingWhich == 0)
			r.drawHandle(gtx, ex, ey, lineH, r.selDraggingWhich == 1)
		} else {
			// Caret drag (long press on blank space): a single handle on the caret.
			cx, cy := handleAt(cursorPos)
			registerDrag(&r.selDragCaret, cx, cy)
			r.selDragsOn[3] = true
			r.drawHandle(gtx, cx, cy, lineH, r.selDraggingWhich == 3)
		}
	}

	textClip.Pop()
	r.displayLineCount = lineCount
	// Store captured layout; derive lastLineY from it.
	r.glyphLayout = layout
	if len(layout.Y) > 0 {
		r.lastLineY = layout.Y[len(layout.Y)-1]
	}
}

// drawHandle draws a selection handle mimicking the native Android
// teardrop: a filled circle below the line with a short stem reaching up
// toward the line, in the system selection blue. (x, y) is the insertion
// point at the top of the line, as returned by handleAt. While the handle
// is being dragged it is drawn enlarged, as the framework does.
func (r *Renderer) drawHandle(gtx layout.Context, x, y, lineH Dp, dragging bool) {
	col := Color{R: 51, G: 153, B: 255, A: 255}
	radius, stemW, stemLen := Dp(10), Dp(3), Dp(12)
	if dragging {
		radius, stemW, stemLen = Dp(13), Dp(4), Dp(15)
	}
	// Stem: from just below the line's bottom up into the line, meeting the
	// top of the circle (2dp overlap avoids a seam between the two shapes).
	circleTop := y + lineH
	r.drawBg(gtx, Region{X: x - stemW/2, Y: circleTop - stemLen, W: stemW, H: stemLen + 2}, col)
	r.drawCircle(gtx, x, circleTop+radius, radius, col)
}

// drawCircle draws a filled circle of radius r centred at (cx, cy), as a
// square RRect clip with all corner radii at half the side.
func (r *Renderer) drawCircle(gtx layout.Context, cx, cy, rad Dp, col Color) {
	rr := clip.UniformRRect(image.Rectangle{
		Min: image.Point{X: int(r.toPx(cx - rad)), Y: int(r.toPx(cy - rad))},
		Max: image.Point{X: int(r.toPx(cx + rad)), Y: int(r.toPx(cy + rad))},
	}, int(r.toPx(rad))).Push(gtx.Ops)
	paint.ColorOp{Color: color.NRGBA{R: col.R, G: col.G, B: col.B, A: col.A}}.Add(gtx.Ops)
	paint.PaintOp{}.Add(gtx.Ops)
	rr.Pop()
}

func (r *Renderer) drawPng(gtx layout.Context, img image.Image, reg Region, width, height Dp) {
	if img == nil {
		return
	}
	// Auto-size: if width or height is 0, use the region dimensions
	w := width
	h := height
	if w == 0 && h == 0 {
		w, h = reg.W, reg.H
	} else if w == 0 {
		w = h
	} else if h == 0 {
		h = w
	}
	xPx := int(r.toPx(reg.X))
	yPx := int(r.toPx(reg.Y))
	wPx := int(r.toPx(w))
	hPx := int(r.toPx(h))
	origW := img.Bounds().Dx()
	origH := img.Bounds().Dy()
	if origW == 0 || origH == 0 {
		return
	}
	sx := float32(wPx) / float32(origW)
	sy := float32(hPx) / float32(origH)
	// Position, then scale so the image fills the target size
	offset := op.Offset(image.Pt(xPx, yPx)).Push(gtx.Ops)
	scale := op.Affine(f32.Affine2D{}.Scale(f32.Pt(0, 0), f32.Pt(sx, sy))).Push(gtx.Ops)
	paint.NewImageOp(img).Add(gtx.Ops)
	paint.PaintOp{}.Add(gtx.Ops)
	scale.Pop()
	offset.Pop()
}

// CaretPoint maps a window-relative byte offset to the insertion point's
// (x, y) in Dp relative to the shaped window's origin, where y is the
// line's baseline. A byte at a real glyph's start sits at the glyph's left
// edge; any other insertion point (a line's terminating "\n", an empty
// line's lone byte, EOF, or a wrapped line's first byte) sits on the visual
// line whose first byte is at or before it — the last such line — at the
// line origin for a line's first byte, and at the last glyph's right edge
// otherwise. (The first glyph at/past such a byte sits on the NEXT line,
// so it cannot be used for the line resolution.)
//
// The line's baseline comes from the uniform shaper grid
// (firstBaseline + line*lineH). firstBaseline is the window's FIRST visual
// line's baseline. When that line is empty (no recorded glyphs), the
// smallest recorded Y is the first NON-empty line's baseline =
// firstBaseline + j*lineH, j being the first recorded glyph's visual line;
// anchoring on the smallest Y instead drew every boundary caret one line
// too low per leading empty line, and the caret visibly jumped a line when
// the window scrolled past the empty line.
func CaretPoint(layout GlyphLayout, str string, byteOff int, ascent, lineH Dp) (x, y Dp) {
	if idx := sort.Search(len(layout.ByteOffsets), func(i int) bool {
		return layout.ByteOffsets[i] >= byteOff
	}); idx < len(layout.ByteOffsets) && layout.ByteOffsets[idx] == byteOff {
		return layout.X[idx], layout.Y[idx]
	}
	line := 0
	lineStart, lineEnd := 0, len(str)
	if starts := layout.VisualLineStarts; len(starts) > 0 {
		k := sort.Search(len(starts), func(i int) bool {
			return starts[i] > byteOff
		})
		if k > 0 {
			line = k - 1
		}
		lineStart = starts[line]
		if k < len(starts) {
			lineEnd = starts[k]
		}
	}
	var anchor Dp
	if len(layout.ByteOffsets) > 0 {
		j := 0
		if starts := layout.VisualLineStarts; len(starts) > 0 {
			if k := sort.Search(len(starts), func(i int) bool {
				return starts[i] > layout.ByteOffsets[0]
			}); k > 0 {
				j = k - 1
			}
		}
		anchor = layout.Y[0] - Dp(j)*lineH
	} else {
		anchor = ascent // no glyphs in the window (pure newlines)
	}
	y = anchor + Dp(line)*lineH
	if byteOff == lineStart {
		return 0, y // line origin (empty line, or wrapped line start)
	}
	// The line's "\n" (or EOF on the last line): the last glyph's right
	// edge on the line.
	var rightX Dp
	found := false
	for i, bo := range layout.ByteOffsets {
		if bo < lineStart || bo >= lineEnd {
			continue
		}
		if xe := layout.X[i] + layout.Advance[i]; !found || xe > rightX {
			rightX, found = xe, true
		}
	}
	return rightX, y
}