From cc63a3aeb7320d8859fee009a970fbed7d1d3187 Mon Sep 17 00:00:00 2001
From: Elias Naur <mail@eliasnaur.com>
Date: Sat, 23 Jan 2021 12:00:50 +0100
Subject: [PATCH] io/router: don't send pointer.Cancel events to disappearing
 handlers

As a follow-up to gioui.org/commit/24f69bf4, this change makes it so
that merely adding a pointer.InputOp doesn't trigger redraws when
the pointer is hovered over its area.

Signed-off-by: Elias Naur <mail@eliasnaur.com>
---
 io/router/pointer.go      | 16 ++++++++++++----
 io/router/pointer_test.go |  9 ++++++---
 2 files changed, 18 insertions(+), 7 deletions(-)

diff --git a/io/router/pointer.go b/io/router/pointer.go
index 77165429..69b475e3 100644
--- a/io/router/pointer.go
+++ b/io/router/pointer.go
@@ -205,7 +205,7 @@ func (q *pointerQueue) hit(areaIdx int, p f32.Point) bool {
 	return true
 }
 
-func (q *pointerQueue) init() {
+func (q *pointerQueue) reset() {
 	if q.handlers == nil {
 		q.handlers = make(map[event.Tag]*pointerHandler)
 	}
@@ -213,7 +213,7 @@ func (q *pointerQueue) init() {
 }
 
 func (q *pointerQueue) Frame(root *op.Ops, events *handlerEvents) {
-	q.init()
+	q.reset()
 	for _, h := range q.handlers {
 		// Reset handler.
 		h.active = false
@@ -238,6 +238,8 @@ func (q *pointerQueue) Frame(root *op.Ops, events *handlerEvents) {
 				for i, k2 := range p.handlers {
 					if k2 == k {
 						// Drop other handlers that lost their grab.
+						cancelHandlers(events, p.handlers[i+1:]...)
+						cancelHandlers(events, p.handlers[:i]...)
 						q.dropHandlers(events, p.handlers[i+1:]...)
 						q.dropHandlers(events, p.handlers[:i]...)
 						break
@@ -248,9 +250,14 @@ func (q *pointerQueue) Frame(root *op.Ops, events *handlerEvents) {
 	}
 }
 
-func (q *pointerQueue) dropHandlers(events *handlerEvents, tags ...event.Tag) {
+func cancelHandlers(events *handlerEvents, tags ...event.Tag) {
 	for _, k := range tags {
 		events.Add(k, pointer.Event{Type: pointer.Cancel})
+	}
+}
+
+func (q *pointerQueue) dropHandlers(events *handlerEvents, tags ...event.Tag) {
+	for _, k := range tags {
 		for i := range q.pointers {
 			p := &q.pointers[i]
 			for i := len(p.handlers) - 1; i >= 0; i-- {
@@ -268,10 +275,11 @@ func (q *pointerQueue) dropHandlers(events *handlerEvents, tags ...event.Tag) {
 }
 
 func (q *pointerQueue) Push(e pointer.Event, events *handlerEvents) {
-	q.init()
+	q.reset()
 	if e.Type == pointer.Cancel {
 		q.pointers = q.pointers[:0]
 		for k := range q.handlers {
+			cancelHandlers(events, k)
 			q.dropHandlers(events, k)
 		}
 		return
diff --git a/io/router/pointer_test.go b/io/router/pointer_test.go
index 5d61a7d4..7161e82a 100644
--- a/io/router/pointer_test.go
+++ b/io/router/pointer_test.go
@@ -89,9 +89,12 @@ func TestPointerMove(t *testing.T) {
 			Type:     pointer.Move,
 			Position: f32.Pt(100, 50),
 		},
+		pointer.Event{
+			Type: pointer.Cancel,
+		},
 	)
-	assertEventSequence(t, r.Events(handler1), pointer.Cancel, pointer.Enter, pointer.Move, pointer.Move, pointer.Leave)
-	assertEventSequence(t, r.Events(handler2), pointer.Cancel, pointer.Enter, pointer.Move, pointer.Leave)
+	assertEventSequence(t, r.Events(handler1), pointer.Cancel, pointer.Enter, pointer.Move, pointer.Move, pointer.Leave, pointer.Cancel)
+	assertEventSequence(t, r.Events(handler2), pointer.Cancel, pointer.Enter, pointer.Move, pointer.Leave, pointer.Cancel)
 }
 
 func TestPointerTypes(t *testing.T) {
@@ -396,7 +399,7 @@ func TestPointerActiveInputDisappears(t *testing.T) {
 			Position: f32.Pt(25, 25),
 		},
 	)
-	assertEventSequence(t, r.Events(handler1), pointer.Cancel)
+	assertEventSequence(t, r.Events(handler1))
 }
 
 func TestMultitouch(t *testing.T) {