Add support for stereoscopic content in QOpenGLWidget

Need to add the plumbing necessary to support two textures in
QOpenGLWidget and use these in the backing store. The changes
required on the RHI level is already done in an earlier patch.
Then paintGL() needs to be called twice, once for each buffer.
Also add overloads for the other functions of QOopenGLWidget
where it makes sense to query for left or right buffer.
Then finally create an example.

[ChangeLog][Widgets][QOpenGLWidget] Added support for
stereoscopic rendering.

Fixes: QTBUG-64587
Change-Id: I5a5c53506dcf8a56442097290dceb7eb730d50ce
Reviewed-by: Laszlo Agocs <laszlo.agocs@qt.io>

1 files changed, 7 insertions, 1 deletions

diff --git a/src/widgets/kernel/qwidget_p.h b/src/widgets/kernel/qwidget_p.h
index 65e368d945..ea03e9c708 100644
--- a/src/widgets/kernel/qwidget_p.h
+++ b/src/widgets/kernel/qwidget_p.h
@@ -579,7 +579,13 @@ public:
 
     virtual QPlatformBackingStoreRhiConfig rhiConfig() const { return {}; }
 
-    virtual QRhiTexture *texture() const { return nullptr; }
+    // Note that textureRight may be null, as it's only used in stereoscopic rendering
+    struct TextureData {
+        QRhiTexture *textureLeft = nullptr;
+        QRhiTexture *textureRight = nullptr;
+    };
+
+    virtual TextureData texture() const { return {}; }
     virtual QPlatformTextureList::Flags textureListFlags() {
         Q_Q(QWidget);
         return q->testAttribute(Qt::WA_AlwaysStackOnTop)