From bec0283e54f155d2a949ab6ae7eb0b074773ffdd Mon Sep 17 00:00:00 2001
From: Elias Naur <mail@eliasnaur.com>
Date: Thu, 14 Apr 2022 18:51:39 +0200
Subject: [PATCH] io/router: deliver synthetic events to sibling pointer
 handlers

Before this change, synthetic events such as scrolling caused by
focus movement would use semantic information to determine potential
receivers. However, there can only be one handler per area so sibling
handlers would not be considered. This change makes the event delivery
traverse the entire tree of handlers, including siblings.

Signed-off-by: Elias Naur <mail@eliasnaur.com>
---
 io/router/key_test.go |  4 ++++
 io/router/pointer.go  | 29 +++++++++++++++++------------
 2 files changed, 21 insertions(+), 12 deletions(-)

diff --git a/io/router/key_test.go b/io/router/key_test.go
index 49763599..c99040df 100644
--- a/io/router/key_test.go
+++ b/io/router/key_test.go
@@ -282,6 +282,10 @@ func TestFocusScroll(t *testing.T) {
 		Types:        pointer.Scroll,
 		ScrollBounds: image.Rect(-100, -100, 100, 100),
 	}.Add(ops)
+	// Test that h is scrolled even if behind another handler.
+	pointer.InputOp{
+		Tag: new(int),
+	}.Add(ops)
 	cl.Pop()
 	parent.Pop()
 	r.Frame(ops)
diff --git a/io/router/pointer.go b/io/router/pointer.go
index 6c1ce31d..e5123ee4 100644
--- a/io/router/pointer.go
+++ b/io/router/pointer.go
@@ -600,17 +600,26 @@ func (q *pointerQueue) pointerOf(e pointer.Event) int {
 // Deliver is like Push, but delivers an event to a particular area.
 func (q *pointerQueue) Deliver(areaIdx int, e pointer.Event, events *handlerEvents) {
 	var sx, sy = e.Scroll.X, e.Scroll.Y
-	for areaIdx != -1 {
-		a := &q.areas[areaIdx]
-		areaIdx = a.parent
-		if !a.semantic.valid {
+	idx := len(q.hitTree) - 1
+	// Locate first potential receiver.
+	for idx != -1 {
+		n := &q.hitTree[idx]
+		if n.area == areaIdx {
+			break
+		}
+		idx--
+	}
+	for idx != -1 {
+		n := &q.hitTree[idx]
+		idx = n.next
+		if n.tag == nil {
 			continue
 		}
-		cnt := a.semantic.content
-		if cnt.tag == nil {
+		h := q.handlers[n.tag]
+		if e.Type&h.types == 0 {
 			continue
 		}
-		h := q.handlers[cnt.tag]
+		e := e
 		if e.Type == pointer.Scroll {
 			if sx == 0 && sy == 0 {
 				break
@@ -619,12 +628,8 @@ func (q *pointerQueue) Deliver(areaIdx int, e pointer.Event, events *handlerEven
 			sx, e.Scroll.X = setScrollEvent(sx, h.scrollRange.Min.X, h.scrollRange.Max.X)
 			sy, e.Scroll.Y = setScrollEvent(sy, h.scrollRange.Min.Y, h.scrollRange.Max.Y)
 		}
-		if e.Type&h.types == 0 {
-			continue
-		}
-		e := e
 		e.Position = q.invTransform(h.area, e.Position)
-		events.Add(cnt.tag, e)
+		events.Add(n.tag, e)
 		if e.Type != pointer.Scroll {
 			break
 		}