Compute glyphLayout after text rendering. Implement correct cursor

movement.

cmd/pad/main.go

@@ -37,6 +37,8 @@ func run(w *app.Window) error {
 	renderer := ui.New(ui.Theme{FontSize: 14}, shaper, logic.State())
 	var mu sync.Mutex
 	var elems []ui.Element
+	var curScale, newScale float32
+
 	log.Printf("run: starting frameReceiver")
 	go frameReceiver(w, &mu, &elems, logic.FrameChan())
 	log.Printf("run: starting logic.Run")
@@ -55,16 +57,13 @@ func run(w *app.Window) error {
 		case app.FrameEvent:
 			log.Printf("run: FrameEvent")
 			gtx := app.NewContext(&ops, e)
-			newScale := gtx.Metric.PxPerDp
-			curScale := logic.State().Scale()
-			if newScale != curScale {
-				logic.ConfigChan() <- editor.ScaleEvent{newScale}
-			}
+			newScale = gtx.Metric.PxPerDp
+			curScale = logic.State().Scale()
 			// Deadlock risk: ensure no channel sends while lock is held
 			mu.Lock()
 			currentElems := elems
 			renderer.Draw(gtx, currentElems)
-			lastLineY := int(renderer.LastLineY())
+			glyphLayout := renderer.GlyphLayout()
 			// Send search query update to the logic goroutine when it changes.
 			// The logic goroutine handles filtering and triggers a new frame.
 			newQuery := logic.State().Browser.SearchEditor.Text()
@@ -112,13 +111,16 @@ func run(w *app.Window) error {
 			}
 			e.Frame(&ops)
 			mu.Unlock()
+			if newScale != curScale {
+				logic.ConfigChan() <- editor.ScaleEvent{newScale}
+			}
 			if len(events) > 0 {
 				logic.InputChan() <- events
 			}
 			if sendQuery {
 				logic.SearchQueryChan() <- newQuery
 			}
-			logic.DisplayLineChan() <- lastLineY
+			logic.LayoutChan() <- glyphLayout
 		}
 	}
 }

doc/editor_implementation_plan.md

@@ -154,7 +154,7 @@ func (r *Renderer) drawWrappedText(...) GlyphLayout {
 }
 ```
 
-`TextField.Draw` will store the returned layout on the renderer for the main loop to pick up.
+`TextField.Draw` calls `drawWrappedText`, which captures the layout as a side effect and stores it on the renderer (`r.glyphLayout`). No code change is needed in `element.go` — the storage happens entirely inside `drawWrappedText` in `render.go`.
 
 ### 8.5 Feedback Path
 
@@ -280,7 +280,7 @@ func HandleCursorMove(delta int) {
 |---|---|---|
 | `internal/ui/unit.go` | No `GlyphLayout` type defined | Add `GlyphLayout` struct |
 | `internal/ui/render.go` | `drawWrappedText` tracks `lastLineY` and `displayLineCount` only | Return `GlyphLayout`; derive `lastLineY` from it; expose via `r.GlyphLayout()` |
-| `internal/ui/element.go` | `TextField.Draw` calls `drawWrappedText` but ignores any layout return value | Store returned `GlyphLayout` on renderer |
+| `internal/ui/element.go` | `TextField.Draw` calls `drawWrappedText` | **No change** — layout capture and storage happens entirely inside `drawWrappedText` in `render.go` |
 | `internal/editor/logic.go` | Uses `lastLineYChan` for feedback | Add `layoutChan`; handle it in `Run()` loop; remove `lastLineYChan` |
 | `internal/editor/state.go` | `EditorLayout` uses fixed-width approximation (`EditorFontSize * 0.6`) and `byteOffsetToLineCol`; `HandleCursorMove` is byte-based (±1) | `EditorState.GlyphLayout` field; `EditorLayout` uses it for cursor positioning; `HandleCursorMove` uses it for navigation |
 | `cmd/pad/main.go` | Sends `int(renderer.LastLineY())` on `DisplayLineChan()` after each frame | Send `r.GlyphLayout()` on `layoutChan` after draw; remove `lastLineYChan` usage |

internal/editor/logic.go

@@ -49,7 +49,7 @@ type Logic struct {
 	configChan       chan ConfigUpdate
 	frameChan        chan []ui.Element
 	inputChan        chan []ui.InputEvent
-	lastLineYChan    chan int // last line Y (Dp, sent as int) feedback from renderer
+	layoutChan       chan ui.GlyphLayout // per-glyph layout feedback from renderer (replaces lastLineYChan)
 	resultChan       chan ResultEvent
 	searchQueryChan  chan string // search text updates from main goroutine
 	openFileChan     chan string // Added for asynchronous file loading
@@ -82,7 +82,7 @@ func NewLogic() *Logic {
 		configChan:      make(chan ConfigUpdate),
 		frameChan:       make(chan []ui.Element),
 		inputChan:       make(chan []ui.InputEvent),
-		lastLineYChan:    make(chan int),
+		layoutChan:      make(chan ui.GlyphLayout),
 		resultChan:       make(chan ResultEvent),
 		searchQueryChan: make(chan string),
 		openFileChan:    make(chan string), // Initialized
@@ -110,9 +110,9 @@ func (l *Logic) InputChan() chan<- []ui.InputEvent {
 	return l.inputChan
 }
 
-// DisplayLineChan returns the last line Y feedback channel.
-func (l *Logic) DisplayLineChan() chan<- int {
-	return l.lastLineYChan
+// LayoutChan returns the glyph layout feedback channel.
+func (l *Logic) LayoutChan() chan<- ui.GlyphLayout {
+	return l.layoutChan
 }
 
 // ResultChan returns the result channel for the logic goroutine.
@@ -148,9 +148,16 @@ func (l *Logic) Run() {
 			log.Printf("Logic: ConfigEvent")
 			update.apply(l.state)
 			l.frameChan <- l.state.layout(l.browserManager)
-		case y := <-l.lastLineYChan:
-			if ui.Dp(y) != l.state.LastLineY {
-				l.state.LastLineY = ui.Dp(y)
+		case layout := <-l.layoutChan:
+			// Store the full GlyphLayout on editor state.
+			// Derive LastLineY from it for scroll clamping.
+			l.state.Editor.GlyphLayout = layout
+			var derivedLastLineY ui.Dp
+			if len(layout.Y) > 0 {
+				derivedLastLineY = layout.Y[len(layout.Y)-1]
+			}
+			if derivedLastLineY != l.state.LastLineY {
+				l.state.LastLineY = derivedLastLineY
 				l.frameChan <- l.state.layout(l.browserManager)
 			}
 		case events := <-l.inputChan:

internal/editor/state.go

@@ -2,6 +2,7 @@ package editor
 
 import (
 	"log"
+	"sort"
 
 	"pad/internal/browser"
 	"pad/internal/ui"
@@ -45,6 +46,7 @@ const (
 type EditorState struct {
 	Buffer         string        // Document content
 	CursorPosition int           // Byte offset
+	GlyphLayout    ui.GlyphLayout // Per-glyph layout from renderer
 	SelectionStart int           // -1 if no selection
 	SelectionEnd   int           // -1 if no selection
 	Dirty          bool          // Needs save
@@ -342,15 +344,35 @@ func EditorLayout(screenWidth, screenHeight ui.Dp, wordWrap bool) []ui.Element {
 	// for Gio to deliver key events to this element.
 	editorElem.Focused = TheState.FocusedElementID == "editor_text"
 
-	// Convert byte offset (CursorPosition) to line/column for cursor rendering.
-	line, col := byteOffsetToLineCol(TheState.Editor.Buffer, TheState.Editor.CursorPosition)
-
-	// Compute cursor X/Y in screen coordinates.
-	// We approximate character width as EditorFontSize * 0.6 for monospace.
-	charWidth := ui.Dp(float32(EditorFontSize) * 0.6)
+	// Position cursor from GlyphLayout.
+	layout := TheState.Editor.GlyphLayout
+	pos := TheState.Editor.CursorPosition
 	lineHeight := EditorLineHeight()
-	cursorX := editorRegion.X + ui.Dp(col)*charWidth
-	cursorY := editorRegion.Y + ui.Dp(line)*lineHeight - TheState.ScrollOffset
+
+	var cursorX, cursorY ui.Dp
+	if len(layout.ByteOffsets) == 0 {
+		// Empty buffer — place cursor at the top-left of the editor region.
+		cursorX = editorRegion.X
+		cursorY = editorRegion.Y
+	} else {
+		// Binary search for the glyph at or after the cursor byte offset.
+		idx := sort.Search(len(layout.ByteOffsets), func(i int) bool {
+			return layout.ByteOffsets[i] >= pos
+		})
+		if idx < len(layout.ByteOffsets) {
+			// Cursor is at a glyph position.
+			cursorX = editorRegion.X + layout.X[idx]
+			cursorY = editorRegion.Y - TheState.ScrollOffset + layout.Y[idx] - EditorFontSize
+		} else {
+			// Cursor is at end of buffer — place after last glyph.
+			cursorX = editorRegion.X + layout.X[len(layout.X)-1] + layout.Advance[len(layout.Advance)-1]
+			cursorY = editorRegion.Y - TheState.ScrollOffset + layout.Y[len(layout.Y)-1] - EditorFontSize
+		}
+	}
+
+	// Derive line/col for bottom bar display (still using byte-based
+	// approximation until GlyphLayout-based line tracking is added).
+	line, col := byteOffsetToLineCol(TheState.Editor.Buffer, TheState.Editor.CursorPosition)
 
 	// Create the cursor element at the computed position
 	cursorElem := ui.NewCursor(

internal/ui/render.go

@@ -8,6 +8,7 @@ import (
 	_ "image/png"
 	"log"
 	"time"
+	"unicode/utf8"
 
 	"gioui.org/f32"
 	"gioui.org/gesture"
@@ -60,8 +61,9 @@ type Renderer struct {
 	clicks            map[string]clickReg
 	Keys              map[string]keyReg // Exported Keys map
 	scrolls           map[string]scrollReg
-	displayLineCount  int    // number of display lines from last drawWrappedText
-	lastLineY         Dp     // last line baseline offset from text origin, in Dp
+	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
 }
 
 // New creates a new Renderer.
@@ -229,6 +231,13 @@ 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 {
@@ -472,12 +481,28 @@ func (r *Renderer) drawWrappedText(gtx layout.Context, str string, reg Region, w
 	var glyphs [32]text.Glyph
 	line := glyphs[:0]
 	lineCount := 0
-	var lastGlyphY float32 // shaper Y value of last glyph drawn
+
+	// Capture per-glyph layout data for cursor positioning and navigation.
+	var layout GlyphLayout
+	byteOffset := 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.
+		layout.ByteOffsets = append(layout.ByteOffsets, byteOffset)
+		layout.X = append(layout.X, Dp(float32(g.X>>6)/r.scale.Scale()))
+		layout.Y = append(layout.Y, Dp(float32(g.Y)/r.scale.Scale()))
+		layout.Advance = append(layout.Advance, Dp(float32(g.Advance>>6)/r.scale.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 {
 			r.drawLine(gtx, line, reg.X, y, col)
-			lastGlyphY = float32(line[len(line)-1].Y)
 			line = line[:0]
 			if g.Flags&text.FlagLineBreak != 0 {
 				lineCount++
@@ -486,7 +511,6 @@ func (r *Renderer) drawWrappedText(gtx layout.Context, str string, reg Region, w
 	}
 	if len(line) > 0 {
 		r.drawLine(gtx, line, reg.X, y, col)
-		lastGlyphY = float32(line[len(line)-1].Y)
 		lineCount++
 	}
 	call := m.Stop()
@@ -494,7 +518,11 @@ func (r *Renderer) drawWrappedText(gtx layout.Context, str string, reg Region, w
 
 	textClip.Pop()
 	r.displayLineCount = lineCount
-	r.lastLineY = Dp(lastGlyphY / r.scale.Scale()) // pixels → Dp
+	// Store captured layout; derive lastLineY from it.
+	r.glyphLayout = layout
+	if len(layout.Y) > 0 {
+		r.lastLineY = layout.Y[len(layout.Y)-1]
+	}
 }
 
 func (r *Renderer) drawPng(gtx layout.Context, img image.Image, reg Region, width, height Dp) {

internal/ui/unit.go

@@ -63,3 +63,15 @@ func FromDp(r Region, scale float32) RegionPx {
 		H: ToPx(r.H, scale),
 	}
 }
+
+// GlyphLayout holds per-glyph layout data captured during text shaping.
+// Each index i represents one glyph (one rune in the source string).
+// ByteOffsets[i] is the byte position in the buffer, (X[i], Y[i]) is the
+// glyph's screen location in Dp (X relative to text region origin, Y is the
+// shaper baseline), and Advance[i] is the glyph's width in Dp.
+type GlyphLayout struct {
+	ByteOffsets []int  // byte offset of each glyph in the buffer
+	X           []Dp   // screen X (Dp) of each glyph, relative to text region origin
+	Y           []Dp   // screen Y (Dp) baseline of each glyph (shaper value)
+	Advance     []Dp   // advance width (Dp) of each glyph
+}