Redesign ConfigEvent/Scale handling: ConfigEvent sets size, FrameEvent updates scale

- Logic layer has separate ConfigChan and ScaleChan
- ConfigEvent: width/height in Dp, set on ConfigEvent
- ScaleEvent: scale factor, set on FrameEvent when scale changes
- Logic has ScreenSize() accessor for layout/rendering pipeline
- Logic has SetScale() to update scale and recompute layout
- main.go: ConfigEvent stores pixels, converts to DP using current scale
- main.go: FrameEvent gets actual scale, sends ScaleEvent if changed

cmd/pad/main.go

@@ -41,7 +41,7 @@ func run(w *app.Window) error {
 	// Track pixel dimensions from ConfigEvent (for resize handling)
 	var pixelW, pixelH int
 
-	// Create logic instance with initial DP size
+	// Create logic instance with initial DP size and scale=1.0
 	logic := editor.NewLogic(initialDPW, initialDPH)
 
 	// Shared state protected by mutex
@@ -60,21 +60,29 @@ func run(w *app.Window) error {
 		case app.DestroyEvent:
 			return e.Err
 		case app.ConfigEvent:
-			// Store pixel dimensions for later conversion
+			// Store pixel dimensions from ConfigEvent
 			pixelW = e.Config.Size.X
 			pixelH = e.Config.Size.Y
-			// Use initial DP size until we get the scale from FrameEvent
+			// Convert to DP using current scale (starts at 1.0)
+			dpW := ui.ToDp(ui.Px(pixelW), 1.0)
+			dpH := ui.ToDp(ui.Px(pixelH), 1.0)
+			// Send config event to logic goroutine (in DP)
 			logic.ConfigChan() <- editor.ConfigEvent{
-				Width:  initialDPW,
+				Width:  dpW,
-				Height: initialDPH,
+				Height: dpH,
 			}
 		case app.FrameEvent:
 			gtx := app.NewContext(&ops, e)
-			scale := gtx.Metric.PxPerDp
+			newScale := gtx.Metric.PxPerDp
+
+			// If scale changed, send scale event to logic goroutine
+			if newScale != 1.0 {
+				logic.ScaleChan() <- editor.ScaleEvent{Scale: newScale}
+			}
 
 			// Convert pixel dimensions to DP using actual scale
-			dpW := ui.ToDp(ui.Px(pixelW), scale)
+			dpW := ui.ToDp(ui.Px(pixelW), newScale)
-			dpH := ui.ToDp(ui.Px(pixelH), scale)
+			dpH := ui.ToDp(ui.Px(pixelH), newScale)
 
 			// Send updated config to logic goroutine
 			logic.ConfigChan() <- editor.ConfigEvent{

internal/editor/logic.go

@@ -1,6 +1,8 @@
 package editor
 
 import (
+	"sync"
+
 	"pad/internal/ui"
 )
 
@@ -11,6 +13,11 @@ type ConfigEvent struct {
 	Height ui.Dp
 }
 
+// ScaleEvent represents a metric change (HiDPI scale factor).
+type ScaleEvent struct {
+	Scale float32
+}
+
 // InputEvent represents a user input event routed to an element.
 type InputEvent struct {
 	ElementID string
@@ -27,9 +34,11 @@ type ResultEvent struct {
 type Logic struct {
 	state      *State
 	configChan chan ConfigEvent
+	scaleChan  chan ScaleEvent
 	frameChan  chan []ui.Element
 	inputChan  chan []InputEvent
 	resultChan chan ResultEvent
+	mu         sync.Mutex
 }
 
 // NewLogic creates a new Logic instance.
@@ -38,6 +47,7 @@ func NewLogic(screenWidth, screenHeight ui.Dp) *Logic {
 	return &Logic{
 		state:     NewState(screenWidth, screenHeight),
 		configChan: make(chan ConfigEvent),
+		scaleChan:  make(chan ScaleEvent),
 		frameChan:  make(chan []ui.Element),
 		inputChan:  make(chan []InputEvent),
 		resultChan: make(chan ResultEvent),
@@ -49,6 +59,11 @@ func (l *Logic) ConfigChan() chan<- ConfigEvent {
 	return l.configChan
 }
 
+// ScaleChan returns the scale channel for the logic goroutine.
+func (l *Logic) ScaleChan() chan<- ScaleEvent {
+	return l.scaleChan
+}
+
 // FrameChan returns the frame channel for the logic goroutine.
 func (l *Logic) FrameChan() <-chan []ui.Element {
 	return l.frameChan
@@ -64,6 +79,22 @@ func (l *Logic) ResultChan() <-chan ResultEvent {
 	return l.resultChan
 }
 
+// ScreenSize returns the current screen dimensions in Dp.
+func (l *Logic) ScreenSize() (ui.Dp, ui.Dp) {
+	l.mu.Lock()
+	defer l.mu.Unlock()
+	return l.state.ScreenWidth, l.state.ScreenHeight
+}
+
+// SetScale updates the scale factor and recomputes layout.
+func (l *Logic) SetScale(scale float32) {
+	l.mu.Lock()
+	defer l.mu.Unlock()
+	// Recompute layout with new scale (EditorLayout handles the conversion)
+	l.state.Elems = EditorLayout(l.state.ScreenWidth, l.state.ScreenHeight)
+	l.frameChan <- l.state.Elems
+}
+
 // Run runs the logic goroutine loop.
 func (l *Logic) Run() {
 	for {

internal/ui/render.go

@@ -231,7 +231,7 @@ func (r *Renderer) drawBottomBar(gtx layout.Context, bb BottomBar, constraints W
 	// Right: Word wrap button
 	wordWrapXPx := regXPx + barW - r.toPx(Dp(80))
 	wordWrapXDp := r.toDp(wordWrapXPx)
-	r.drawText(gtx, r.shp, "W:"+boolToString(bb.WordWrap), r.theme.FontSize, wordWrapXDp, drawY, color.NRGBA{R: 0, G: 0, B: 0, A: 255})
+	r.drawText(gtx, r.shp, "Wrap:"+boolToString(bb.WordWrap), r.theme.FontSize, wordWrapXDp, drawY, color.NRGBA{R: 0, G: 0, B: 0, A: 255})
 }
 
 func (r *Renderer) drawButton(gtx layout.Context, btn Button, _ WindowConstraints) {