widget: add semantic descriptions

Some semantic information is automatically extracted, but some must be
provided by UI components. This change enriches the generic and material
widgets with such information.

Signed-off-by: Elias Naur <mail@eliasnaur.com>

widget/widget_test.go

@@ -0,0 +1,61 @@
+// SPDX-License-Identifier: Unlicense OR MIT
+
+package widget_test
+
+import (
+	"image"
+	"testing"
+
+	"gioui.org/f32"
+	"gioui.org/io/pointer"
+	"gioui.org/io/router"
+	"gioui.org/io/semantic"
+	"gioui.org/io/system"
+	"gioui.org/layout"
+	"gioui.org/op"
+	"gioui.org/widget"
+)
+
+func TestBool(t *testing.T) {
+	var (
+		ops op.Ops
+		r   router.Router
+		b   widget.Bool
+	)
+	gtx := layout.NewContext(&ops, system.FrameEvent{Queue: &r})
+	layout := func() {
+		b.Layout(gtx, func(gtx layout.Context) layout.Dimensions {
+			semantic.CheckBox.Add(gtx.Ops)
+			semantic.DescriptionOp("description").Add(gtx.Ops)
+			return layout.Dimensions{Size: image.Pt(100, 100)}
+		})
+	}
+	layout()
+	r.Frame(gtx.Ops)
+	r.Queue(
+		pointer.Event{
+			Source:   pointer.Touch,
+			Type:     pointer.Press,
+			Position: f32.Pt(50, 50),
+		},
+		pointer.Event{
+			Source:   pointer.Touch,
+			Type:     pointer.Release,
+			Position: f32.Pt(50, 50),
+		},
+	)
+	ops.Reset()
+	layout()
+	r.Frame(gtx.Ops)
+	tree := r.AppendSemantics(nil)
+	n := tree[0].Children[0].Desc
+	if n.Description != "description" {
+		t.Errorf("unexpected semantic description: %s", n.Description)
+	}
+	if n.Class != semantic.CheckBox {
+		t.Errorf("unexpected semantic class: %v", n.Class)
+	}
+	if !b.Value || !n.Selected {
+		t.Error("click did not select")
+	}
+}