xcb: Support EGLStreams for Wayland on X11

To make NVidia EGLStreams work on the desktop, we need to use eglGetPlatformDisplayEXT
instead of eglGetDisplay. Therefore, let's try that first if we have the extension.

Change-Id: Id420fb46d5bc5345faa5cbb066584b0859d50417
Reviewed-by: Laszlo Agocs <laszlo.agocs@qt.io>

src/platformsupport/eglconvenience/qeglstreamconvenience_p.h

@@ -140,6 +140,10 @@ typedef EGLBoolean (EGLAPIENTRYP PFNEGLSTREAMCONSUMEROUTPUTEXTPROC) (EGLDisplay
 #define EGL_DRM_PLANE_EXT                 0x3235
 #endif
 
+#ifndef EGL_PLATFORM_X11_KHR
+#define EGL_PLATFORM_X11_KHR              0x31D5
+#endif
+
 QT_BEGIN_NAMESPACE
 
 class QEGLStreamConvenience

src/plugins/platforms/xcb/gl_integrations/xcb_egl/qxcbeglintegration.cpp

@@ -42,6 +42,7 @@
 #include "qxcbeglcontext.h"
 
 #include <QtGui/QOffscreenSurface>
+#include <QtPlatformSupport/private/qeglstreamconvenience_p.h>
 
 #include "qxcbeglnativeinterfacehandler.h"
 
@@ -63,6 +64,17 @@ QXcbEglIntegration::~QXcbEglIntegration()
 bool QXcbEglIntegration::initialize(QXcbConnection *connection)
 {
     m_connection = connection;
+
+    const char *extensions = eglQueryString(EGL_NO_DISPLAY, EGL_EXTENSIONS);
+
+    if (extensions && strstr(extensions, "EGL_EXT_platform_x11")) {
+        QEGLStreamConvenience streamFuncs;
+        m_egl_display = streamFuncs.get_platform_display(EGL_PLATFORM_X11_KHR,
+                                                         xlib_display(),
+                                                         nullptr);
+    }
+
+    if (!m_egl_display)
         m_egl_display = eglGetDisplay(reinterpret_cast<EGLNativeDisplayType>(xlib_display()));
 
     EGLint major, minor;