wasm: support adding and removing canvases at runtime

Add qtloader API:
  addCanvasElement()
  removeCanvasElement()

These functions call the corresponding add/remove screen
functions on QWasmIntegration.

Task-number: QTBUG-64079
Change-Id: I537c11f3b5fb9240cca9b6313dd45f803d865ac6
Reviewed-by: Morten Johan Sørvig <morten.sorvig@qt.io>

src/plugins/platforms/wasm/qtloader.js

@@ -118,6 +118,10 @@
 //      "Exited", iff crashed is false.
 // exitText
 //      Abort/exit message.
+// addCanvasElement
+//      Add canvas at run-time. Adds a corresponding QScreen,
+// removeCanvasElement
+//      Remove canvas at run-time. Removes the corresponding QScreen.
 
 
 var Module = {}
@@ -227,6 +231,8 @@ function QtLoader(config)
     publicAPI.canLoadApplication = canLoadQt();
     publicAPI.status = undefined;
     publicAPI.loadEmscriptenModule = loadEmscriptenModule;
+    publicAPI.addCanvasElement = addCanvasElement;
+    publicAPI.removeCanvasElement = removeCanvasElement;
 
     restartCount = 0;
 
@@ -528,6 +534,20 @@ function QtLoader(config)
         window.setTimeout(function() { handleStatusChange(); }, 0);
     }
 
+    function addCanvasElement(element) {
+        if (publicAPI.status == "Running")
+            Module.qtAddCanvasElement(element);
+        else
+            console.log("Error: addCanvasElement can only be called in the Running state");
+    }
+
+    function removeCanvasElement(element) {
+        if (publicAPI.status == "Running")
+            Module.qtRemoveCanvasElement(element);
+        else
+            console.log("Error: removeCanvasElement can only be called in the Running state");
+    }
+
     setStatus("Created");
 
     return publicAPI;

src/plugins/platforms/wasm/qwasmintegration.cpp

@@ -61,9 +61,23 @@ static void browserBeforeUnload(emscripten::val)
     QWasmIntegration::QWasmBrowserExit();
 }
 
+static void addCanvasElement(emscripten::val canvas)
+{
+    QString canvasId = QString::fromStdString(canvas["id"].as<std::string>());
+    QWasmIntegration::get()->addScreen(canvasId);
+}
+
+static void removeCanvasElement(emscripten::val canvas)
+{
+    QString canvasId = QString::fromStdString(canvas["id"].as<std::string>());
+    QWasmIntegration::get()->removeScreen(canvasId);
+}
+
 EMSCRIPTEN_BINDINGS(qtQWasmIntegraton)
 {
     function("qtBrowserBeforeUnload", &browserBeforeUnload);
+    function("qtAddCanvasElement", &addCanvasElement);
+    function("qtRemoveCanvasElement", &removeCanvasElement);
 }
 
 QWasmIntegration *QWasmIntegration::s_instance;
@@ -99,8 +113,9 @@ QWasmIntegration::~QWasmIntegration()
 {
     delete m_fontDb;
 
-    while (!m_screens.isEmpty())
+    for (auto it = m_screens.constBegin(); it != m_screens.constEnd(); ++it)
-        QWindowSystemInterface::handleScreenRemoved(m_screens.takeLast());
+        QWindowSystemInterface::handleScreenRemoved(*it);
+    m_screens.clear();
 
     s_instance = nullptr;
 }
@@ -184,17 +199,17 @@ QPlatformClipboard* QWasmIntegration::clipboard() const
     return m_clipboard;
 }
 
-QVector<QWasmScreen *> QWasmIntegration::screens()
-{
-    return m_screens;
-}
-
 void QWasmIntegration::addScreen(const QString &canvasId)
 {
     QWasmScreen *screen = new QWasmScreen(canvasId);
     m_clipboard->installEventHandlers(canvasId);
-    m_screens.append(screen);
+    m_screens.insert(canvasId, screen);
     QWindowSystemInterface::handleScreenAdded(screen);
 }
 
+void QWasmIntegration::removeScreen(const QString &canvasId)
+{
+    QWindowSystemInterface::handleScreenRemoved(m_screens.take(canvasId));
+}
+
 QT_END_NAMESPACE

src/plugins/platforms/wasm/qwasmintegration.h

@@ -70,21 +70,20 @@ public:
     QStringList themeNames() const override;
     QPlatformTheme *createPlatformTheme(const QString &name) const override;
     QPlatformClipboard *clipboard() const override;
-
-    QVector<QWasmScreen *>screens();
     QWasmClipboard *getWasmClipboard() { return m_clipboard; }
 
     static QWasmIntegration *get() { return s_instance; }
     static void QWasmBrowserExit();
 
-private:
     void addScreen(const QString &canvasId);
+    void removeScreen(const QString &canvasId);
 
+private:
     mutable QWasmFontDatabase *m_fontDb;
     mutable QWasmEventDispatcher *m_eventDispatcher;
     mutable QHash<QWindow *, QWasmBackingStore *> m_backingStores;
 
-    QVector<QWasmScreen *> m_screens;
+    QHash<QString, QWasmScreen *> m_screens;
     mutable QWasmClipboard *m_clipboard;
     static QWasmIntegration *s_instance;
 };