wasm: fix onLoaded delay functionality

onLoaded and the initial expose/paint should be sequenced
such that onLoaded is fired first, followed by the expose.
This makes sure that we don't spend any time on painting
frames before Qt is completely initialized.

Add a "requestUpdateHold" mode to QWasmCompositor (initially
on) which disables requestUpdate calls, as well
as releaseRequestUpdateHold() which enables requestUpdate
calls again. This is a one-way transition; the mode
can't be enabled again.

This amends commit f2e22774 which implemented the concept
of startup tasks, where onLoaded can be delayed until
for instance font loading has been completed. After
this commit the expose event and initial commit will
be delayed as well.

Change-Id: Icc784306726174fbabe8785d54485860e968745a
Reviewed-by: Lorn Potter <lorn.potter@gmail.com>
Reviewed-by: Piotr Wierciński <piotr.wiercinski@qt.io>

1 files changed, 17 insertions, 10 deletions

diff --git a/src/corelib/kernel/qeventdispatcher_wasm.cpp b/src/corelib/kernel/qeventdispatcher_wasm.cpp
index 5f4c46c07f..f5061f35d7 100644
--- a/src/corelib/kernel/qeventdispatcher_wasm.cpp
+++ b/src/corelib/kernel/qeventdispatcher_wasm.cpp
@@ -218,9 +218,12 @@ QEventDispatcherWasm::QEventDispatcherWasm()
 #if QT_CONFIG(thread)
         g_mainThread = pthread_self();
 #endif
+
         // Call the "onLoaded" JavaScript callback, unless startup tasks
-        // have been registered which should complete first.
-        checkCallQtLoaded();
+        // have been registered which should complete first. Run async
+        // to make sure event dispatcher construction (in particular any
+        // subclass construction) has completed first.
+        runAsync(callOnLoadedIfRequired);
     } else {
 #if QT_CONFIG(thread)
         std::lock_guard<std::mutex> lock(g_staticDataMutex);
@@ -916,10 +919,10 @@ void QEventDispatcherWasm::registerStartupTask()
 void QEventDispatcherWasm::completeStarupTask()
 {
     --g_startupTasks;
-    checkCallQtLoaded();
+    callOnLoadedIfRequired();
 }
 
-void QEventDispatcherWasm::checkCallQtLoaded()
+void QEventDispatcherWasm::callOnLoadedIfRequired()
 {
     if (g_startupTasks > 0)
         return;
@@ -929,12 +932,16 @@ void QEventDispatcherWasm::checkCallQtLoaded()
         return;
     qtLoadedCalled = true;
 
-    QTimer::singleShot(0, [](){
-        emscripten::val qt = emscripten::val::module_property("qt");
-        if (qt.isUndefined())
-            return;
-        qt.call<void>("onLoaded");
-    });
+    Q_ASSERT(g_mainThreadEventDispatcher);
+    g_mainThreadEventDispatcher->onLoaded();
+}
+
+void QEventDispatcherWasm::onLoaded()
+{
+    emscripten::val qt = emscripten::val::module_property("qt");
+    if (qt.isUndefined())
+        return;
+    qt.call<void>("onLoaded");
 }
 
 namespace {