Update shaper_usage.md with correct glyph drawing approach

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

doc/shaper_usage.md

@@ -159,34 +159,52 @@ func charWidths(gtx layout.Context, shp *text.Shaper, str string, size unit.Sp)
 
 ## 5. Rendering Glyphs Directly
 
-Instead of using `material.Label()` (which shapes text again), draw glyphs directly:
+Gio's textView draws glyphs using `shaper.Shape()` (for vector glyphs) and `shaper.Bitmaps()` (for bitmap glyphs like emoji). This is the correct approach to avoid double-shaping.
 
-### 5.1 Drawing a Single Glyph
+### 5.1 Drawing Text Using Gio's textView Approach
 
 ```go
-// After layout, iterate through glyphs
-for {
-    g, ok := shp.NextGlyph()
-    if !ok {
-        break
+func drawText(gtx layout.Context, shp *text.Shaper, str string, size unit.Sp, x, y unit.Dp, col color.NRGBA) {
+    // Layout text
+    shp.LayoutString(text.Parameters{PxPerEm: fixed.I(gtx.Sp(size))}, str)
+
+    // Draw glyphs using the same approach as Gio's textView
+    var glyphs [32]text.Glyph
+    line := glyphs[:0]
+    for g, ok := shp.NextGlyph(); ok; g, ok = shp.NextGlyph() {
+        line = append(line, g)
+        if g.Flags&text.FlagLineBreak != 0 || cap(line)-len(line) == 0 {
+            drawLine(gtx, shp, line, x, y, col)
+            line = line[:0]
+        }
     }
-    // Draw glyph at position (g.X, g.Y)
-    // Use shp.DrawGlyph() or manual drawing
+    if len(line) > 0 {
+        drawLine(gtx, shp, line, x, y, col)
+    }
+}
+
+func drawLine(gtx layout.Context, shp *text.Shaper, line []text.Glyph, x, y unit.Dp, col color.NRGBA) {
+    // Apply offset transform
+    off := f32.Point{X: float32(x), Y: float32(y)}
+    t := op.Affine(f32.Affine2D{}.Offset(off)).Push(gtx.Ops)
+
+    // Draw vector glyphs
+    path := shp.Shape(line)
+    outline := clip.Outline{Path: path}.Op().Push(gtx.Ops)
+    paint.ColorOp{Color: col}.Add(gtx.Ops)
+    paint.PaintOp{}.Add(gtx.Ops)
+    outline.Pop()
+
+    // Draw bitmap glyphs (emoji, etc.)
+    if call := shp.Bitmaps(line); call != (op.CallOp{}) {
+        call.Add(gtx.Ops)
+    }
+
+    t.Pop()
 }
 ```
 
-### 5.2 Using Shaper's Drawing Functions
-
-The shaper provides drawing functions that use the already-computed glyph data:
-
-```go
-// Draw all laid-out glyphs
-shp.Draw(gtx, ops, color.NRGBA{R: 0, G: 0, B: 0, A: 255})
-```
-
-**Important**: Call `shp.Draw()` AFTER calling `LayoutString()` or `Layout()`. The drawing functions use the glyph data computed during the layout phase.
-
-### 5.3 Avoiding Double-Shaping
+### 5.2 Avoiding Double-Shaping
 
 **WRONG** (shapes text twice):
 
@@ -198,14 +216,19 @@ widths := charWidths(gtx, shp, text, size)
 material.Label(th, size, text).Layout(gtx)
 ```
 
-**CORRECT** (shapes text once):
+**CORRECT** (shapes text once for rendering):
 
 ```go
-// Single pass: layout and draw
-shp.LayoutString(text.Parameters{PxPerEm: fixed.I(gtx.Sp(size))}, text)
-shp.Draw(gtx, ops, color.NRGBA{R: 0, G: 0, B: 0, A: 255})
+// Single pass: layout and draw using shaper.Shape()
+drawText(gtx, shp, text, size, x, y, col)
 ```
 
+**NOTE**: For truncation, we may need to layout twice:
+1. First layout to measure widths and find truncation point
+2. Second layout to draw the truncated text
+
+This is acceptable because truncation is only needed when text doesn't fit, and the string is short (filename in StatusBar).
+
 ## 6. Comparison with Gio's textView
 
 Gio's textView (`widget/text.go`) demonstrates the correct approach: