fix(ui): TextArea 接收滚轮，内容超出时可滚动

components/textarea.go

@@ -553,6 +553,26 @@ func (layout *TextareaLayout) ScrollBy(dy float32) {
 	layout.scroll = layout.clampScroll(layout.scroll + dy)
 }
 
+// Wheel scrolls the box by a wheel event over the text it last painted, as ScrollBy does, and
+// reports whether the box moved. A wheel the box cannot move with (it is at the end the wheel
+// points to, or it shows all its rows) reports false, so the page scrolls instead.
+func (layout *TextareaLayout) Wheel(event gfx.ScrollEvent) bool {
+	content := layout.content
+	if !layout.painted || event.X < content.X || event.X >= content.X+content.Width ||
+		event.Y < content.Y || event.Y >= content.Y+content.Height {
+		return false
+	}
+	dy := event.DeltaY
+	if !event.Precise && dy > 0 && dy < 24 {
+		dy = 24
+	} else if !event.Precise && dy < 0 && dy > -24 {
+		dy = -24
+	}
+	before := layout.scroll
+	layout.ScrollBy(dy)
+	return layout.scroll != before
+}
+
 // RowCount is how many rows text takes in a box of outer width width: one for
 // each line that fits and as many as a longer one wraps to, and an empty one
 // after a final newline. The rows it wraps are the ones the next paint at that

components/textarea_wheel_test.go

@@ -0,0 +1,45 @@
+package components
+
+import (
+	"strings"
+	"testing"
+
+	"github.com/vivaui/viva/gfx"
+)
+
+// A wheel over a TextareaLayout scrolls it while it can move in that direction, and reports
+// nothing once it is at the end, so the page can scroll instead.
+func TestTextareaWheelScrollsUntilItsEnd(t *testing.T) {
+	var lines []string
+	for index := range 40 {
+		lines = append(lines, "row "+string(rune('a'+index%26)))
+	}
+	text := strings.Join(lines, "\n")
+	box := newWrapBox(t, 100)
+	box.paint(TextareaSnapshot{Value: text, Caret: 0})
+	center := gfx.Point{X: box.layout.content.X + 4, Y: box.layout.content.Y + 4}
+
+	outside := gfx.ScrollEvent{X: box.layout.content.X - 10, Y: center.Y, DeltaY: 30}
+	if box.layout.Wheel(outside) {
+		t.Fatal("a wheel outside the text scrolled the box")
+	}
+	up := gfx.ScrollEvent{X: center.X, Y: center.Y, DeltaY: -30}
+	if box.layout.Wheel(up) {
+		t.Fatal("a wheel up at the top scrolled the box")
+	}
+
+	down := gfx.ScrollEvent{X: center.X, Y: center.Y, DeltaY: 30}
+	if !box.layout.Wheel(down) {
+		t.Fatal("a wheel down over the text did not scroll the box")
+	}
+	for range 200 {
+		box.paint(TextareaSnapshot{Value: text, Caret: 0})
+		if !box.layout.Wheel(down) {
+			break
+		}
+	}
+	box.paint(TextareaSnapshot{Value: text, Caret: 0})
+	if box.layout.Wheel(down) {
+		t.Fatal("a wheel down at the end of the text still scrolled the box")
+	}
+}

ui/page.go

@@ -1127,6 +1127,13 @@ func (p *Page) Wheel(event gfx.ScrollEvent) gfx.EventResult {
 			return state.Wheel(event)
 		}
 	}
+	// A TextArea under the pointer scrolls its own rows first; at its end the wheel goes on
+	// to the page, as in a browser.
+	for _, entry := range p.fields {
+		if entry.field.rows && entry.field.area != nil && entry.field.area.Wheel(event) {
+			return gfx.EventResult{Handled: true, Repaint: true}
+		}
+	}
 	if p.wheelRoute != nil {
 		if result, ok := p.wheelRoute(p, event); ok {
 			return result