wasm: fix texture leak when window is destroyed in a different context

Reproduce:
Show first window in first canvas;
Show second window in second canvas;
After screens are rendered destroy first window in first canvas

Change-Id: Ifbeb4824c1fdedecf24d5d20e58613d15c066420
Reviewed-by: Morten Johan Sørvig <morten.sorvig@qt.io>

src/plugins/platforms/wasm/qwasmbackingstore.cpp

@@ -36,7 +36,7 @@
 #include <QtGui/qpainter.h>
 #include <private/qguiapplication_p.h>
 #include <qpa/qplatformscreen.h>
-
+#include <QtGui/qoffscreensurface.h>
 #include <QtGui/qbackingstore.h>
 
 QT_BEGIN_NAMESPACE
@@ -53,12 +53,29 @@ QWasmBackingStore::QWasmBackingStore(QWasmCompositor *compositor, QWindow *windo
 
 QWasmBackingStore::~QWasmBackingStore()
 {
+    auto window = this->window();
+    QWasmIntegration::get()->removeBackingStore(window);
+    destroy();
+    QWasmWindow *wasmWindow = static_cast<QWasmWindow *>(window->handle());
+    if (wasmWindow)
+        wasmWindow->setBackingStore(nullptr);
 }
 
 void QWasmBackingStore::destroy()
 {
-    if (m_texture->isCreated())
-        m_texture->destroy();
+    if (m_texture->isCreated()) {
+        auto context = m_compositor->context();
+        auto currentContext = QOpenGLContext::currentContext();
+        if (!currentContext || !QOpenGLContext::areSharing(context, currentContext)) {
+            QOffscreenSurface offScreenSurface(m_compositor->screen()->screen());
+            offScreenSurface.setFormat(context->format());
+            offScreenSurface.create();
+            context->makeCurrent(&offScreenSurface);
+            m_texture->destroy();
+        } else {
+            m_texture->destroy();
+        }
+    }
 }
 
 QPaintDevice *QWasmBackingStore::paintDevice()
@@ -81,9 +98,9 @@ void QWasmBackingStore::updateTexture()
     if (m_dirty.isNull())
         return;
 
-    if (m_recreateTexture && m_texture->isCreated()) {
+    if (m_recreateTexture) {
         m_recreateTexture = false;
-        m_texture->destroy();
+        destroy();
     }
 
     if (!m_texture->isCreated()) {

src/plugins/platforms/wasm/qwasmcompositor.cpp

@@ -59,7 +59,6 @@ QWasmCompositedWindow::QWasmCompositedWindow()
 
 QWasmCompositor::QWasmCompositor(QWasmScreen *screen)
     :QObject(screen)
-    , m_frameBuffer(nullptr)
     , m_blitter(new QOpenGLTextureBlitter)
     , m_needComposit(false)
     , m_inFlush(false)
@@ -71,7 +70,6 @@ QWasmCompositor::QWasmCompositor(QWasmScreen *screen)
 
 QWasmCompositor::~QWasmCompositor()
 {
-    delete m_frameBuffer;
     destroy();
 }
 
@@ -748,3 +746,8 @@ QWasmScreen *QWasmCompositor::screen()
 {
     return static_cast<QWasmScreen *>(parent());
 }
+
+QOpenGLContext *QWasmCompositor::context()
+{
+    return m_context.data();
+}

src/plugins/platforms/wasm/qwasmcompositor.h

@@ -125,11 +125,13 @@ public:
     static QWasmTitleBarOptions makeTitleBarOptions(const QWasmWindow *window);
     static QRect titlebarRect(QWasmTitleBarOptions tb, QWasmCompositor::SubControls subcontrol);
 
+    QWasmScreen *screen();
+    QOpenGLContext *context();
+
 private slots:
     void frame();
 
 private:
-    QWasmScreen *screen();
     void notifyTopWindowChanged(QWasmWindow *window);
     void drawWindow(QOpenGLTextureBlitter *blitter, QWasmScreen *screen, QWasmWindow *window);
     void drawWindowContent(QOpenGLTextureBlitter *blitter, QWasmScreen *screen, QWasmWindow *window);
@@ -138,7 +140,6 @@ private:
     void drawWindowDecorations(QOpenGLTextureBlitter *blitter, QWasmScreen *screen, QWasmWindow *window);
     void drwPanelButton();
 
-    QImage *m_frameBuffer;
     QScopedPointer<QOpenGLContext> m_context;
     QScopedPointer<QOpenGLTextureBlitter> m_blitter;
 

src/plugins/platforms/wasm/qwasmintegration.cpp

@@ -193,6 +193,11 @@ QPlatformBackingStore *QWasmIntegration::createPlatformBackingStore(QWindow *win
 #endif
 }
 
+void QWasmIntegration::removeBackingStore(QWindow* window)
+{
+    m_backingStores.remove(window);
+}
+
 #ifndef QT_NO_OPENGL
 QPlatformOpenGLContext *QWasmIntegration::createPlatformOpenGLContext(QOpenGLContext *context) const
 {

src/plugins/platforms/wasm/qwasmintegration.h

@@ -88,6 +88,7 @@ public:
     void resizeScreen(const QString &canvasId);
     void resizeAllScreens();
     void updateDpi();
+    void removeBackingStore(QWindow* window);
 
 private:
     mutable QWasmFontDatabase *m_fontDb;