Store scale in State, use it everywhere instead of gtx.Metric.PxPerDp

- State.Scale stores the scale factor (default 1.0)
- ScaleEvent applies SetScale() which updates State.Scale
- Logic.Scale() accessor returns current scale
- Renderer.SetScale() updates renderer's scale from State
- main.go: uses logic.Scale() to get scale, calls renderer.SetScale()
- No more references to gtx.Metric.PxPerDp in render.go or main.go

cmd/pad/main.go

@@ -40,8 +40,6 @@ func run(w *app.Window) error {
 
 	// Track pixel dimensions from ConfigEvent (for resize handling)
 	var pixelW, pixelH int
-	// Track previous scale to detect changes
-	scale := float32(1.0)
 
 	// Create logic instance with initial DP size and scale=1.0
 	logic := editor.NewLogic(initialDPW, initialDPH)
@@ -75,13 +73,9 @@ func run(w *app.Window) error {
 			}
 		case app.FrameEvent:
 			gtx := app.NewContext(&ops, e)
-			newScale := gtx.Metric.PxPerDp
 
-			// If scale changed, send scale event to logic goroutine
-			if newScale != scale {
-				logic.ConfigChan() <- editor.ScaleEvent{Scale: newScale}
-				scale = newScale
-			}
+			// Get scale from State — this is updated by ScaleEvent
+			newScale := logic.Scale()
 
 			// Convert pixel dimensions to DP using actual scale
 			dpW := ui.ToDp(ui.Px(pixelW), newScale)
@@ -93,6 +87,9 @@ func run(w *app.Window) error {
 				Height: dpH,
 			}
 
+			// Update renderer with current scale from State
+			renderer.SetScale(newScale)
+
 			// Acquire mutex, read frame, draw, release mutex
 			mu.Lock()
 			currentElems := elems

internal/editor/logic.go

@@ -31,9 +31,7 @@ func (e ConfigEvent) apply(s *State) {
 }
 
 func (e ScaleEvent) apply(s *State) {
-	// Scale is used by the renderer, not stored in state.
-	// Layout is already computed in DP, so no recomputation needed.
-	_ = s.Elems // force use of state
+	s.SetScale(e.Scale)
 }
 
 // InputEvent represents a user input event routed to an element.
@@ -98,6 +96,13 @@ func (l *Logic) ScreenSize() (ui.Dp, ui.Dp) {
 	return l.state.ScreenWidth, l.state.ScreenHeight
 }
 
+// Scale returns the current scale factor (pixels per DP).
+func (l *Logic) Scale() float32 {
+	l.mu.Lock()
+	defer l.mu.Unlock()
+	return l.state.Scale
+}
+
 // Run runs the logic goroutine loop.
 func (l *Logic) Run() {
 	for {
@@ -109,8 +114,7 @@ func (l *Logic) Run() {
 				e.apply(l.state)
 				l.frameChan <- l.state.Elems
 			case ScaleEvent:
-				// Scale is used by the renderer via gtx.Metric.PxPerDp.
-				// No state change needed — layout is already in DP.
+				e.apply(l.state)
 				l.frameChan <- l.state.Elems
 			}
 		case <-l.inputChan:

internal/editor/state.go

@@ -9,19 +9,28 @@ import (
 type State struct {
 	ScreenWidth  ui.Dp
 	ScreenHeight ui.Dp
+	Scale        float32 // pixels per DP, default 1.0
 	Elems        []ui.Element
 }
 
 // NewState creates a new State with initial editor layout.
 // screenWidth and screenHeight are in device-independent pixels (Dp).
+// scale defaults to 1.0 until updated by ScaleEvent.
 func NewState(screenWidth, screenHeight ui.Dp) *State {
 	return &State{
 		ScreenWidth:  screenWidth,
 		ScreenHeight: screenHeight,
+		Scale:        1.0,
 		Elems:        EditorLayout(screenWidth, screenHeight),
 	}
 }
 
+// SetScale updates the scale factor and recomputes layout.
+func (s *State) SetScale(scale float32) {
+	s.Scale = scale
+	s.Elems = EditorLayout(s.ScreenWidth, s.ScreenHeight)
+}
+
 // EditorLayout computes regions for the editor page.
 // It takes screen dimensions in Dp and returns []Element with regions in Dp.
 // This function works exclusively in Dp — no pixel conversions.

internal/ui/render.go

@@ -19,7 +19,7 @@ import (
 type Renderer struct {
 	theme Theme
 	shp   *text.Shaper
-	scale float32 // pixels per DP, from gtx.Metric.PxPerDp
+	scale float32 // pixels per DP, from State.Scale
 }
 
 // New creates a new Renderer.
@@ -27,9 +27,9 @@ func New(th Theme, shp *text.Shaper) *Renderer {
 	return &Renderer{theme: th, shp: shp, scale: 1.0}
 }
 
-// setScale updates the renderer's scale factor from a layout.Context.
-func (r *Renderer) setScale(gtx layout.Context) {
-	r.scale = gtx.Metric.PxPerDp
+// SetScale updates the renderer's scale factor from State.Scale.
+func (r *Renderer) SetScale(scale float32) {
+	r.scale = scale
 }
 
 // toPx converts Dp to physical pixels using the renderer's scale.
@@ -45,10 +45,8 @@ func (r *Renderer) toDp(px Px) Dp {
 // Draw iterates elements and draws each in slice order (back-to-front).
 // It captures the initial constraints once at the start, then passes them
 // to each render function for consistent positioning.
+// The scale is set externally via SetScale() from State.Scale.
 func (r *Renderer) Draw(gtx layout.Context, elems []Element) {
-	// Update scale from the frame context
-	r.setScale(gtx)
-
 	// Capture initial constraints once — before any clips modify them.
 	// These are in physical pixels and serve as the window bounds for all positioning.
 	initialConstraints := WindowConstraints{