wasm: sync pointer button state on pointer down

We may get PointerDown events with "no buttons" as the button
state in some cases such as for tap events on Apple trackpads.

Make sure the mouse button which caused the pointer down
event is in the mouse buttons set for the event.

Fixes: QTBUG-108639
Pick-to: 6.4 6.5
Change-Id: I0a49abc398308bbfed657b99fc74f60c16e05a59
Reviewed-by: Morten Johan Sørvig <morten.sorvig@qt.io>

1 files changed, 8 insertions, 0 deletions

diff --git a/src/plugins/platforms/wasm/qwasmevent.cpp b/src/plugins/platforms/wasm/qwasmevent.cpp
index d4f9991feb..19730c2c68 100644
--- a/src/plugins/platforms/wasm/qwasmevent.cpp
+++ b/src/plugins/platforms/wasm/qwasmevent.cpp
@@ -44,6 +44,14 @@ std::optional<PointerEvent> PointerEvent::fromWeb(emscripten::val event)
         PointerType::Mouse : PointerType::Other;
     ret.mouseButton = MouseEvent::buttonFromWeb(event["button"].as<int>());
     ret.mouseButtons = MouseEvent::buttonsFromWeb(event["buttons"].as<unsigned short>());
+
+    // The current button state (event.buttons) may be out of sync for some PointerDown
+    // events where the "down" state is very brief, for example taps on Apple trackpads.
+    // Qt expects that the current button state is in sync with the event, so we sync
+    // it up here.
+    if (*eventType == EventType::PointerDown)
+        ret.mouseButtons |= ret.mouseButton;
+
     ret.localPoint = QPoint(event["offsetX"].as<int>(), event["offsetY"].as<int>());
     ret.pointInPage = QPoint(event["pageX"].as<int>(), event["pageY"].as<int>());
     ret.pointInViewport = QPoint(event["clientX"].as<int>(), event["clientY"].as<int>());