Improve window dragging on WASM

Window dragging has been considerably improved by replacing the mouse
events by pointer events and placing a pointer lock on WASM canvas, so
that off-browser window events are delivered to us.

Translation of the drag origin has been limited to inside the canvas, so
that a window cannot be dragged so far that it becomes offscreen and is
unreachable.

Change-Id: Id177c630a6466f04464a513371d6b97d3a098b6a
Reviewed-by: Lorn Potter <lorn.potter@gmail.com>

1 files changed, 145 insertions, 0 deletions

diff --git a/src/plugins/platforms/wasm/qwasmevent.h b/src/plugins/platforms/wasm/qwasmevent.h
new file mode 100644
index 0000000000..784591fb95
--- /dev/null
+++ b/src/plugins/platforms/wasm/qwasmevent.h
@@ -0,0 +1,145 @@
+// Copyright (C) 2022 The Qt Company Ltd.
+// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GPL-3.0-only
+
+#ifndef QWASMEVENT_H
+#define QWASMEVENT_H
+
+#include "qwasmplatform.h"
+
+#include <QtCore/qglobal.h>
+#include <QtCore/qnamespace.h>
+
+#include <QPoint>
+
+#include <emscripten/html5.h>
+#include <emscripten/val.h>
+
+QT_BEGIN_NAMESPACE
+
+enum class EventType {
+    PointerDown,
+    PointerMove,
+    PointerUp,
+    PointerEnter,
+    PointerLeave,
+};
+
+enum class PointerType {
+    Mouse,
+    Other,
+};
+
+namespace KeyboardModifier {
+namespace internal
+{
+    // Check for the existence of shiftKey, ctrlKey, altKey and metaKey in a type.
+    // Based on that, we can safely assume we are dealing with an emscripten event type.
+    template<typename T>
+    struct IsEmscriptenEvent
+    {
+        template<typename U, EM_BOOL U::*, EM_BOOL U::*, EM_BOOL U::*, EM_BOOL U::*>
+        struct SFINAE {};
+        template<typename U> static char Test(
+            SFINAE<U, &U::shiftKey, &U::ctrlKey, &U::altKey, &U::metaKey>*);
+        template<typename U> static int Test(...);
+        static const bool value = sizeof(Test<T>(0)) == sizeof(char);
+    };
+
+    template<class T, typename Enable = void>
+    struct Helper;
+
+    template<class T>
+    struct Helper<T, std::enable_if_t<IsEmscriptenEvent<T>::value>>
+    {
+        static QFlags<Qt::KeyboardModifier> getModifierForEvent(const T& event) {
+            QFlags<Qt::KeyboardModifier> keyModifier = Qt::NoModifier;
+            if (event.shiftKey)
+                keyModifier |= Qt::ShiftModifier;
+            if (event.ctrlKey)
+                keyModifier |= platform() == Platform::MacOS ? Qt::MetaModifier : Qt::ControlModifier;
+            if (event.altKey)
+                keyModifier |= Qt::AltModifier;
+            if (event.metaKey)
+                keyModifier |= platform() == Platform::MacOS ? Qt::ControlModifier : Qt::MetaModifier;
+
+            return keyModifier;
+        }
+    };
+
+    template<>
+    struct Helper<emscripten::val>
+    {
+        static QFlags<Qt::KeyboardModifier> getModifierForEvent(const emscripten::val& event) {
+            QFlags<Qt::KeyboardModifier> keyModifier = Qt::NoModifier;
+            if (event["shiftKey"].as<bool>())
+                keyModifier |= Qt::ShiftModifier;
+            if (event["ctrlKey"].as<bool>())
+                keyModifier |= platform() == Platform::MacOS ? Qt::MetaModifier : Qt::ControlModifier;
+            if (event["altKey"].as<bool>())
+                keyModifier |= Qt::AltModifier;
+            if (event["metaKey"].as<bool>())
+                keyModifier |= platform() == Platform::MacOS ? Qt::ControlModifier : Qt::MetaModifier;
+            if (event["constructor"]["name"].as<std::string>() == "KeyboardEvent" &&
+                event["location"].as<unsigned int>() == DOM_KEY_LOCATION_NUMPAD) {
+                keyModifier |= Qt::KeypadModifier;
+            }
+
+            return keyModifier;
+        }
+    };
+}  // namespace internal
+
+template <typename Event>
+QFlags<Qt::KeyboardModifier> getForEvent(const Event& event)
+{
+    return internal::Helper<Event>::getModifierForEvent(event);
+}
+
+template <>
+QFlags<Qt::KeyboardModifier> getForEvent<EmscriptenKeyboardEvent>(
+    const EmscriptenKeyboardEvent& event);
+
+}  // namespace KeyboardModifier
+
+struct Q_CORE_EXPORT Event
+{
+    EventType type;
+};
+
+struct Q_CORE_EXPORT MouseEvent : public Event
+{
+    QPoint point;
+    Qt::MouseButton mouseButton;
+    Qt::MouseButtons mouseButtons;
+    QFlags<Qt::KeyboardModifier> modifiers;
+
+    static constexpr Qt::MouseButton buttonFromWeb(int webButton) {
+        switch (webButton) {
+            case 0:
+                return Qt::LeftButton;
+            case 1:
+                return Qt::MiddleButton;
+            case 2:
+                return Qt::RightButton;
+            default:
+                return Qt::NoButton;
+        }
+    }
+
+    static constexpr Qt::MouseButtons buttonsFromWeb(unsigned short webButtons) {
+        // Coincidentally, Qt and web bitfields match.
+        return Qt::MouseButtons::fromInt(webButtons);
+}
+};
+
+struct Q_CORE_EXPORT PointerEvent : public MouseEvent
+{
+    static std::optional<PointerEvent> fromWeb(emscripten::val webEvent);
+
+    PointerType pointerType;
+    int pointerId;
+};
+
+QT_END_NAMESPACE
+
+#endif  // QWASMEVENT_H