all: [API] deliver key events to the first matching filter

Replace the key.Filter.Target field with a Focus field that matches only
of the specified tag has focus. This has the advantage of simpler event
delivery and for lower latency in delivering key events to new handlers.

For example, consider a UI where a button is activated by a key press,
which is turn displays a dialog with another button activated by the
same key. This change allows two button press(+releases) in the same frame
to arrive at the intended targets: one key press(+release) for each
button.

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

widget/button.go

@@ -147,17 +147,12 @@ func (b *Clickable) Update(gtx layout.Context) (Click, bool) {
 			})
 		}
 	}
-	filters := []event.Filter{
-		key.FocusFilter{Target: b},
-	}
-	if b.focused {
-		filters = append(filters,
-			key.Filter{Target: b, Name: key.NameReturn},
-			key.Filter{Target: b, Name: key.NameSpace},
-		)
-	}
 	for {
-		e, ok := gtx.Event(filters...)
+		e, ok := gtx.Event(
+			key.FocusFilter{Target: b},
+			key.Filter{Focus: b, Name: key.NameReturn},
+			key.Filter{Focus: b, Name: key.NameSpace},
+		)
 		if !ok {
 			break
 		}

widget/editor.go

@@ -333,57 +333,47 @@ func (e *Editor) clickDragEvents(gtx layout.Context) []event.Event {
 	return combinedEvents
 }
 
+func condFilter(pred bool, f key.Filter) event.Filter {
+	if pred {
+		return f
+	} else {
+		return nil
+	}
+}
+
 func (e *Editor) processKey(gtx layout.Context) {
 	if e.text.Changed() {
 		e.events = append(e.events, ChangeEvent{})
 	}
-	filters := []event.Filter{key.FocusFilter{Target: e}, transfer.TargetFilter{Target: e, Type: "application/text"}}
-	if e.focused {
-		filters = append(filters,
-			key.Filter{Target: e, Name: key.NameEnter, Optional: key.ModShift},
-			key.Filter{Target: e, Name: key.NameReturn, Optional: key.ModShift},
+	caret, _ := e.text.Selection()
+	atBeginning := caret == 0
+	atEnd := caret == e.text.Len()
+	if gtx.Locale.Direction.Progression() != system.FromOrigin {
+		atEnd, atBeginning = atBeginning, atEnd
+	}
+	filters := []event.Filter{
+		key.FocusFilter{Target: e},
+		transfer.TargetFilter{Target: e, Type: "application/text"},
+		key.Filter{Focus: e, Name: key.NameEnter, Optional: key.ModShift},
+		key.Filter{Focus: e, Name: key.NameReturn, Optional: key.ModShift},
 
-			key.Filter{Target: e, Name: "Z", Required: key.ModShortcut, Optional: key.ModShift},
-			key.Filter{Target: e, Name: "C", Required: key.ModShortcut},
-			key.Filter{Target: e, Name: "V", Required: key.ModShortcut},
-			key.Filter{Target: e, Name: "X", Required: key.ModShortcut},
-			key.Filter{Target: e, Name: "A", Required: key.ModShortcut},
+		key.Filter{Focus: e, Name: "Z", Required: key.ModShortcut, Optional: key.ModShift},
+		key.Filter{Focus: e, Name: "C", Required: key.ModShortcut},
+		key.Filter{Focus: e, Name: "V", Required: key.ModShortcut},
+		key.Filter{Focus: e, Name: "X", Required: key.ModShortcut},
+		key.Filter{Focus: e, Name: "A", Required: key.ModShortcut},
 
-			key.Filter{Target: e, Name: key.NameDeleteBackward, Optional: key.ModShortcutAlt | key.ModShift},
-			key.Filter{Target: e, Name: key.NameDeleteForward, Optional: key.ModShortcutAlt | key.ModShift},
+		key.Filter{Focus: e, Name: key.NameDeleteBackward, Optional: key.ModShortcutAlt | key.ModShift},
+		key.Filter{Focus: e, Name: key.NameDeleteForward, Optional: key.ModShortcutAlt | key.ModShift},
 
-			key.Filter{Target: e, Name: key.NameHome, Optional: key.ModShift},
-			key.Filter{Target: e, Name: key.NameEnd, Optional: key.ModShift},
-			key.Filter{Target: e, Name: key.NamePageDown, Optional: key.ModShift},
-			key.Filter{Target: e, Name: key.NamePageUp, Optional: key.ModShift},
-		)
-		caret, _ := e.text.Selection()
-		if caret > 0 {
-			if gtx.Locale.Direction.Progression() == system.FromOrigin {
-				filters = append(filters,
-					key.Filter{Target: e, Name: key.NameLeftArrow, Optional: key.ModShortcutAlt | key.ModShift},
-					key.Filter{Target: e, Name: key.NameUpArrow, Optional: key.ModShortcutAlt | key.ModShift},
-				)
-			} else {
-				filters = append(filters,
-					key.Filter{Target: e, Name: key.NameRightArrow, Optional: key.ModShortcutAlt | key.ModShift},
-					key.Filter{Target: e, Name: key.NameDownArrow, Optional: key.ModShortcutAlt | key.ModShift},
-				)
-			}
-		}
-		if caret < e.text.Len() {
-			if gtx.Locale.Direction.Progression() == system.FromOrigin {
-				filters = append(filters,
-					key.Filter{Target: e, Name: key.NameRightArrow, Optional: key.ModShortcutAlt | key.ModShift},
-					key.Filter{Target: e, Name: key.NameDownArrow, Optional: key.ModShortcutAlt | key.ModShift},
-				)
-			} else {
-				filters = append(filters,
-					key.Filter{Target: e, Name: key.NameLeftArrow, Optional: key.ModShortcutAlt | key.ModShift},
-					key.Filter{Target: e, Name: key.NameUpArrow, Optional: key.ModShortcutAlt | key.ModShift},
-				)
-			}
-		}
+		key.Filter{Focus: e, Name: key.NameHome, Optional: key.ModShift},
+		key.Filter{Focus: e, Name: key.NameEnd, Optional: key.ModShift},
+		key.Filter{Focus: e, Name: key.NamePageDown, Optional: key.ModShift},
+		key.Filter{Focus: e, Name: key.NamePageUp, Optional: key.ModShift},
+		condFilter(!atBeginning, key.Filter{Focus: e, Name: key.NameLeftArrow, Optional: key.ModShortcutAlt | key.ModShift}),
+		condFilter(!atBeginning, key.Filter{Focus: e, Name: key.NameUpArrow, Optional: key.ModShortcutAlt | key.ModShift}),
+		condFilter(!atEnd, key.Filter{Focus: e, Name: key.NameRightArrow, Optional: key.ModShortcutAlt | key.ModShift}),
+		condFilter(!atEnd, key.Filter{Focus: e, Name: key.NameDownArrow, Optional: key.ModShortcutAlt | key.ModShift}),
 	}
 	// adjust keeps track of runes dropped because of MaxLen.
 	var adjust int

widget/editor_test.go

@@ -1177,6 +1177,29 @@ func TestEditor_Submit(t *testing.T) {
 	}
 }
 
+func TestNoFilterAllocs(t *testing.T) {
+	b := testing.Benchmark(func(b *testing.B) {
+		r := new(input.Router)
+		e := new(Editor)
+		gtx := layout.Context{
+			Ops: new(op.Ops),
+			Constraints: layout.Constraints{
+				Max: image.Pt(100, 100),
+			},
+			Locale: english,
+			Source: r.Source(),
+		}
+		b.ReportAllocs()
+		b.ResetTimer()
+		for i := 0; i < b.N; i++ {
+			e.Update(gtx)
+		}
+	})
+	if allocs := b.AllocsPerOp(); allocs != 0 {
+		t.Fatalf("expected 0 AllocsPerOp, got %d", allocs)
+	}
+}
+
 // textWidth is a text helper for building simple selection events.
 // It assumes single-run lines, which isn't safe with non-test text
 // data.

widget/enum.go

@@ -64,17 +64,12 @@ func (e *Enum) Update(gtx layout.Context) bool {
 				}
 			}
 		}
-		filters := []event.Filter{
-			key.FocusFilter{Target: &state.tag},
-		}
-		if e.focused && e.focus == state.key {
-			filters = append(filters,
-				key.Filter{Target: &state.tag, Name: key.NameReturn},
-				key.Filter{Target: &state.tag, Name: key.NameSpace},
-			)
-		}
 		for {
-			ev, ok := gtx.Event(filters...)
+			ev, ok := gtx.Event(
+				key.FocusFilter{Target: &state.tag},
+				key.Filter{Focus: &state.tag, Name: key.NameReturn},
+				key.Filter{Focus: &state.tag, Name: key.NameSpace},
+			)
 			if !ok {
 				break
 			}

widget/selectable.go

@@ -301,28 +301,23 @@ func (e *Selectable) clickDragEvents(gtx layout.Context) []event.Event {
 }
 
 func (e *Selectable) processKey(gtx layout.Context) {
-	filters := []event.Filter{
-		key.FocusFilter{Target: e},
-	}
-	if e.focused {
-		filters = append(filters,
-			key.Filter{Target: e, Name: key.NameLeftArrow, Optional: key.ModShortcutAlt | key.ModShift},
-			key.Filter{Target: e, Name: key.NameRightArrow, Optional: key.ModShortcutAlt | key.ModShift},
-			key.Filter{Target: e, Name: key.NameUpArrow, Optional: key.ModShortcutAlt | key.ModShift},
-			key.Filter{Target: e, Name: key.NameDownArrow, Optional: key.ModShortcutAlt | key.ModShift},
-
-			key.Filter{Target: e, Name: key.NamePageUp, Optional: key.ModShift},
-			key.Filter{Target: e, Name: key.NamePageDown, Optional: key.ModShift},
-			key.Filter{Target: e, Name: key.NameEnd, Optional: key.ModShift},
-			key.Filter{Target: e, Name: key.NameHome, Optional: key.ModShift},
-
-			key.Filter{Target: e, Name: "C", Required: key.ModShortcut},
-			key.Filter{Target: e, Name: "X", Required: key.ModShortcut},
-			key.Filter{Target: e, Name: "A", Required: key.ModShortcut},
-		)
-	}
 	for {
-		ke, ok := gtx.Event(filters...)
+		ke, ok := gtx.Event(
+			key.FocusFilter{Target: e},
+			key.Filter{Focus: e, Name: key.NameLeftArrow, Optional: key.ModShortcutAlt | key.ModShift},
+			key.Filter{Focus: e, Name: key.NameRightArrow, Optional: key.ModShortcutAlt | key.ModShift},
+			key.Filter{Focus: e, Name: key.NameUpArrow, Optional: key.ModShortcutAlt | key.ModShift},
+			key.Filter{Focus: e, Name: key.NameDownArrow, Optional: key.ModShortcutAlt | key.ModShift},
+
+			key.Filter{Focus: e, Name: key.NamePageUp, Optional: key.ModShift},
+			key.Filter{Focus: e, Name: key.NamePageDown, Optional: key.ModShift},
+			key.Filter{Focus: e, Name: key.NameEnd, Optional: key.ModShift},
+			key.Filter{Focus: e, Name: key.NameHome, Optional: key.ModShift},
+
+			key.Filter{Focus: e, Name: "C", Required: key.ModShortcut},
+			key.Filter{Focus: e, Name: "X", Required: key.ModShortcut},
+			key.Filter{Focus: e, Name: "A", Required: key.ModShortcut},
+		)
 		if !ok {
 			break
 		}