Implement per-pixel smooth scrolling for ListView

- Changed BrowserScrollOffset and ListView.ScrollOffset from int (row index)
  to ui.Dp (pixel offset) for smooth per-pixel scrolling
- Updated HandleBrowserScroll to use raw Dp delta instead of row-based
  scrolling with minimum ±1 row jumps
- Fixed search not triggering new frames by detecting query changes in
  main.go FrameEvent handler
- Fixed click misalignment by indexing RowFilenames with local index i
  instead of rowGlobalIndex
- Fixed bottom clamping using actual BrowserListHeight and corrected
  formula: maxScroll = totalRows * rowHeight - BrowserListHeight

cmd/pad/main.go

@@ -59,6 +59,13 @@ func run(w *app.Window) error {
 			currentElems := elems
 			renderer.Draw(gtx, currentElems)
 			logic.DisplayLineChan() <- int(renderer.LastLineY())
+			// Check for search query change — trigger a new frame if the
+			// widget.Editor text differs from the logic's stored query.
+			// This ensures the filtered list updates as the user types.
+			newQuery := logic.State().SearchEditor.Text()
+			if newQuery != logic.State().SearchQuery {
+				logic.InputChan() <- []ui.InputEvent{}
+			}
 			if events := renderer.CheckGestures(e.Source, gtx.Metric); len(events) > 0 {
 				logic.InputChan() <- events
 			}

internal/editor/state.go

@@ -72,7 +72,8 @@ type State struct {
 	MaxScroll        ui.Dp      // max scroll offset (content height - viewport height)
 	Elems            []ui.Element
 	// Browser state
-	BrowserScrollOffset int      // index of first visible browser entry
+	BrowserScrollOffset ui.Dp // pixel-level scroll offset for browser list
+	BrowserListHeight   ui.Dp // height of the list region, set during layout
 	SortMode            SortMode // sort mode for browser list
 	SortOrderLabel      string   // label text for sort order toggle
 	SearchQuery         string   // current search query
@@ -107,7 +108,7 @@ func (s *State) layout() []ui.Element {
 	if s.page == BrowserPage {
 		newQuery := s.SearchEditor.Text()
 		if newQuery != s.SearchQuery {
-			s.BrowserScrollOffset = 0
+			s.BrowserScrollOffset = 0 // reset on query change
 		}
 		s.SearchQuery = newQuery
 	}
@@ -140,31 +141,37 @@ func HandleScroll(data any) {
 }
 
 // HandleBrowserScroll updates the browser list scroll offset.
-// The delta is in pixels; convert to Dp, then to row index offset.
+// The delta is in pixels; convert to Dp for smooth per-pixel scrolling.
 func HandleBrowserScroll(data any) {
 	delta := data.(int) // pixels
 	deltaDp := ui.ToDp(ui.Px(delta), TheState.scale)
-	rowHeight := ui.Dp(48)
-	rowDelta := int(deltaDp / rowHeight)
-	// Ensure at least ±1 for non-zero scroll events
-	if rowDelta == 0 && delta != 0 {
-		if delta > 0 {
-			rowDelta = 1
-		} else {
-			rowDelta = -1
-		}
-	}
-	fmt.Printf("HandleBrowserScroll: %d\n", delta)
-	TheState.BrowserScrollOffset += rowDelta
+	TheState.BrowserScrollOffset += deltaDp
 	if TheState.BrowserScrollOffset < 0 {
 		TheState.BrowserScrollOffset = 0
 	}
-	maxOffset := len(getFilteredEntries()) - visibleBrowserRows(TheState.PixelHeight, TheState.scale)
-	if TheState.BrowserScrollOffset > maxOffset {
-		TheState.BrowserScrollOffset = maxOffset
+	maxScroll := computeBrowserMaxScroll()
+	if TheState.BrowserScrollOffset > maxScroll {
+		TheState.BrowserScrollOffset = maxScroll
 	}
 }
 
+// computeBrowserMaxScroll returns the maximum scroll offset in Dp
+// so the last row is fully visible at the bottom of the list.
+func computeBrowserMaxScroll() ui.Dp {
+	rowHeight := ui.Dp(48)
+	totalRows := len(getFilteredEntries())
+	// Calculate max scroll such that the last row's bottom edge
+	// aligns with the list region's bottom edge.
+	// lastRowBottom = totalRows * rowHeight
+	// We want: lastRowBottom - maxScroll = BrowserListHeight
+	// Therefore: maxScroll = totalRows * rowHeight - BrowserListHeight
+	maxScroll := ui.Dp(totalRows)*rowHeight - TheState.BrowserListHeight
+	if maxScroll < 0 {
+		return 0
+	}
+	return maxScroll
+}
+
 // visibleBrowserRows estimates how many browser rows fit in the viewport.
 func visibleBrowserRows(pixelHeight int, scale float32) int {
 	margin := 10
@@ -397,14 +404,25 @@ func BrowserLayout(screenWidth, screenHeight ui.Dp, sortMode SortMode) []ui.Elem
 		X: margin, Y: listY,
 		W: contentWidth, H: listHeight,
 	}
+	// Store list height for scroll clamping calculation
+	TheState.BrowserListHeight = listHeight
 	// Filter entries by search query (case-insensitive substring match)
 	filteredEntries := getFilteredEntries()
-	visibleEntries := filteredEntries[TheState.BrowserScrollOffset:]
+	// Compute first visible row from Dp scroll offset
+	rowHeight := ui.Dp(48)
+	firstVisibleRow := int(TheState.BrowserScrollOffset / rowHeight)
+	if firstVisibleRow < 0 {
+		firstVisibleRow = 0
+	}
+	if firstVisibleRow > len(filteredEntries) {
+		firstVisibleRow = len(filteredEntries)
+	}
+	visibleEntries := filteredEntries[firstVisibleRow:]
 	list := ui.NewListView(
 		"browser_list",
 		visibleEntries,
 		listRegion,
-		TheState.BrowserScrollOffset,
+		TheState.BrowserScrollOffset, // Dp, not row index
 		-1, // Selected: none
 		[]ui.Interaction{{Gesture: ui.Scroll, Handler: HandleBrowserScroll}},
 	)

internal/ui/element.go

@@ -196,7 +196,7 @@ type ListView struct {
 	visible      bool
 	interactions []Interaction
 	Items        []ListItem
-	ScrollOffset int
+	ScrollOffset Dp // pixel-level scroll offset
 	Selected     int
 	RowFilenames []string // filenames for click navigation
 }
@@ -235,25 +235,27 @@ func (lv ListView) Draw(gtx layout.Context, r *Renderer) {
 		}
 	}
 	rowHeight := Dp(48)
+	firstVisibleRow := int(lv.ScrollOffset / rowHeight)
 	for i, item := range lv.Items {
+		// Account for scroll offset: row Y is shifted up by scroll amount
+		rowGlobalIndex := firstVisibleRow + i
+		y := lv.region.Y + Dp(rowGlobalIndex)*rowHeight - lv.ScrollOffset
 		// Only draw visible rows (virtualized)
-		y := lv.region.Y + Dp(i)*rowHeight
 		if y+rowHeight < lv.region.Y || y > lv.region.Y+lv.region.H {
 			continue
 		}
 		// Draw background for selected item
 		if item.Selected || (lv.Selected == i) {
 			r.drawBg(gtx, Region{
-				X: lv.region.X, Y: lv.region.Y + Dp(i)*rowHeight,
+				X: lv.region.X, Y: y,
 				W: lv.region.W, H: rowHeight,
 			}, Color{R: 200, G: 220, B: 255, A: 255})
 		}
 		// Register click area for this row
-		rowGlobalIndex := lv.ScrollOffset + i
 		rowID := fmt.Sprintf("list_row_%d", rowGlobalIndex)
 		var filename string
-		if rowGlobalIndex < len(lv.RowFilenames) {
-			filename = lv.RowFilenames[rowGlobalIndex]
+		if i < len(lv.RowFilenames) {
+			filename = lv.RowFilenames[i]
 		}
 		r.RegisterClick(gtx, rowID, Region{
 			X: lv.region.X, Y: y,
@@ -264,7 +266,7 @@ func (lv ListView) Draw(gtx layout.Context, r *Renderer) {
 		// Draw main text
 		textRegion := Region{
 			X: lv.region.X + Dp(8),
-			Y: lv.region.Y + Dp(i)*rowHeight + Dp(4),
+			Y: y + Dp(4),
 			W: lv.region.W - Dp(32),
 			H: rowHeight - Dp(8),
 		}
@@ -273,7 +275,7 @@ func (lv ListView) Draw(gtx layout.Context, r *Renderer) {
 		if item.Subtext != "" {
 			subRegion := Region{
 				X: lv.region.X + Dp(8),
-				Y: lv.region.Y + Dp(i)*rowHeight + rowHeight - Dp(22),
+				Y: y + rowHeight - Dp(22),
 				W: lv.region.W - Dp(32),
 				H: Dp(16),
 			}
@@ -283,7 +285,7 @@ func (lv ListView) Draw(gtx layout.Context, r *Renderer) {
 }
 
 // NewListView creates a visible ListView element.
-func NewListView(id string, items []ListItem, region Region, scrollOffset, selected int, interactions []Interaction) ListView {
+func NewListView(id string, items []ListItem, region Region, scrollOffset Dp, selected int, interactions []Interaction) ListView {
 	return ListView{
 		id:           id,
 		region:       region,