Clean up debug statements, restore proper icons, document multi-line text spacing

Co-authored-by: Qwen-Coder <qwen-coder@alibabacloud.com>

doc/shaper_usage.md

@@ -476,12 +476,110 @@ Look for:
 - **Text off-screen**: Wrong offset calculation
 - **Text clipped**: Clip region doesn't include text bounds
 
+## 9. Multi-line Text Spacing
+
+When laying out multiple lines of text at different positions, you need to understand how Gio calculates baseline spacing.
+
+### 9.1 Gio's Line Height Calculation
+
+In `gio/text/gotext.go` (`calculateYOffsets` and `LayoutRunes`):
+
+```go
+// First line baseline starts at the ascent height
+currentY := lines[0].ascent.Ceil()
+
+// Subsequent baselines are spaced by lineHeight
+for i := range lines {
+    if i > 0 {
+        currentY += lines[i].lineHeight.Round()
+    }
+    lines[i].yOffset = currentY
+}
+
+// lineHeight = max(ascent + descent) * LineHeightScale
+// Default LineHeightScale = 1.2
+if params.LineHeight != 0 {
+    maxHeight = params.LineHeight
+}
+if params.LineHeightScale == 0 {
+    params.LineHeightScale = 1.2
+}
+maxHeight = floatToFixed(fixedToFloat(maxHeight) * params.LineHeightScale)
+```
+
+**Key points**:
+- **First line baseline**: `ascent.Ceil()` (not 0)
+- **Baseline-to-baseline spacing**: `lineHeight * LineHeightScale`
+- **Default LineHeightScale**: 1.2 (adds 20% extra padding)
+- **LineHeightScale 1.0**: tightest spacing, no extra padding
+
+### 9.2 Positioning Multiple Lines
+
+When drawing multiple lines at different positions (e.g., filename + icons in StatusBar), use the baseline spacing as your guide:
+
+```go
+// Line 1: Filename at origin
+filenameLineY := reg.Y
+
+// Line 2: Icons — baseline spacing ≈ font size with LineHeightScale=1.0
+// For 16SP font: baseline-to-baseline ≈ 20DP
+iconsLineY := filenameLineY + unit.Dp(20)
+```
+
+**Why 20DP?** For a 16SP font on a typical display:
+- `PxPerEm = 16 * 1.25 = 20` device pixels (2x display)
+- `ascent + descent ≈ PxPerEm = 20`
+- With `LineHeightScale = 1.0`: baseline spacing = 20DP
+
+### 9.3 Controlling Spacing
+
+You have two options to control line spacing:
+
+**Option A: Set `LineHeightScale` in LayoutString**
+```go
+shp.LayoutString(text.Parameters{
+    PxPerEm:         fixed.I(gtx.Sp(size)),
+    MinWidth:        0,
+    MaxWidth:        availableWidth,
+    MaxLines:        1,
+    LineHeightScale: 1.0,  // Tight spacing, no extra padding
+}, str)
+```
+
+**Option B: Set `LineHeight` to a specific value**
+```go
+shp.LayoutString(text.Parameters{
+    PxPerEm:   fixed.I(gtx.Sp(size)),
+    MinWidth:  0,
+    MaxWidth:  availableWidth,
+    MaxLines:  1,
+    LineHeight: fixed.I(gtx.Sp(18)),  // Fixed 18SP baseline spacing
+}, str)
+```
+
+### 9.4 Common Mistakes
+
+**Mistake**: Adding arbitrary spacing between lines without considering baseline positioning.
+
+**Fix**: Remember that the shaper's Y value is the **baseline**, not the top of the text. The visual top of the text is at `baseline - ascent`. So the visual gap between two lines is:
+
+```
+visualGap = (line2Baseline - line1Baseline) - (ascent1 + ascent2)
+          = lineHeight - (ascent1 + ascent2)
+```
+
+With `LineHeightScale = 1.0`: `visualGap ≈ 0` (lines touch)
+With `LineHeightScale = 1.2`: `visualGap ≈ 0.2 * lineHeight` (20% padding)
+
 ## 10. Summary
 
 - **Always** use `fixed.I(gtx.Sp(size))` for `PxPerEm`
 - **Always** set `MinWidth`, `MaxWidth`, `MaxLines` in `LayoutString` parameters
 - **Always** offset by `(x + first.X, y + first.Y)` in `drawLine`
 - **Always** wrap glyph drawing in `op.Record`/`m.Stop()` for clipping
+- **Baseline spacing** = `lineHeight * LineHeightScale` (default 1.2)
+- **For tight multi-line layouts**, use `LineHeightScale: 1.0` or set explicit `LineHeight`
+- **Visual gap** between lines = `baselineSpacing - (ascent1 + ascent2)`
 - **Avoid** using `material.Label()` when you need precise glyph positions
 - **Reuse** glyph data for measurement, hit testing, and rendering
 - **Follow** Gio's `paintGlyph` as the reference implementation

internal/ui/render.go

@@ -90,7 +90,6 @@ func (r *Renderer) drawStatusBar(gtx layout.Context, sb StatusBar) {
 
 	// Line 1: Filename (truncated with ellipsis if needed)
 	filenameLineY := reg.Y
-	filenameLineH := unit.Dp(24)
 
 	// Truncate filename only if it doesn't fit
 	displayFilename := sb.Filename
@@ -117,8 +116,9 @@ func (r *Renderer) drawStatusBar(gtx layout.Context, sb StatusBar) {
 	// Layout filename, measure widths, and draw in a single pass
 	r.drawTruncatedText(gtx, th.Shaper, displayFilename, r.theme.FontSize, reg.X+unit.Dp(8), filenameLineY, availableWidth, spaceForText, color.NRGBA{R: 0, G: 0, B: 0, A: 255})
 
-	// Line 2: Icons
-	iconsLineY := filenameLineY + filenameLineH
+	// Line 2: Icons — positioned 20DP below filename baseline.
+	// This matches Gio's default line spacing (ascent+descent with LineHeightScale=1.0).
+	iconsLineY := filenameLineY + unit.Dp(20)
 
 	// Left side: Cut, Copy, Paste icons
 	leftX := reg.X + unit.Dp(8)