Force Qt to use GLES if desktop GL is not available

Some platforms like the VisionFive 2 don't have working desktop GL,
so they must use GLES to be able to render at all. Qt doesn't try
to fall back if it fails to find a compatible EGL config, so we must
do so ourselves.

app/main.cpp

@@ -550,7 +550,9 @@ int main(int argc, char *argv[])
 #endif
     }
 
-    if (WMUtils::isRunningNvidiaProprietaryDriverX11() || qEnvironmentVariableIntValue("FORCE_QT_GLES")) {
+    if (WMUtils::isRunningNvidiaProprietaryDriverX11() ||
+        !WMUtils::supportsDesktopGLWithEGL() ||
+        qEnvironmentVariableIntValue("FORCE_QT_GLES")) {
         // The Nvidia proprietary driver causes Qt to render a black window when using
         // the default Desktop GL profile with EGL. AS a workaround, we default to
         // OpenGL ES when running on Nvidia on X11.

app/utils.h

@@ -8,6 +8,7 @@
 namespace WMUtils {
     bool isRunningX11();
     bool isRunningNvidiaProprietaryDriverX11();
+    bool supportsDesktopGLWithEGL();
     bool isRunningWayland();
     bool isRunningWindowManager();
     bool isRunningDesktopEnvironment();

app/wm.cpp

@@ -88,6 +88,45 @@ bool WMUtils::isRunningNvidiaProprietaryDriverX11()
 #endif
 }
 
+bool WMUtils::supportsDesktopGLWithEGL()
+{
+#ifdef HAVE_EGL
+    static SDL_atomic_t supportsDesktopGL;
+
+    // If the value is not set yet, populate it now.
+    int val = SDL_AtomicGet(&supportsDesktopGL);
+    if (!(val & VALUE_SET)) {
+        bool desktopGL = false;
+
+        EGLDisplay display = eglGetDisplay(EGL_DEFAULT_DISPLAY);
+        if (display != EGL_NO_DISPLAY && eglInitialize(display, nullptr, nullptr)) {
+            EGLint matchingConfigs = 0;
+            EGLint const attribs[] =
+            {
+                EGL_SURFACE_TYPE, EGL_WINDOW_BIT,
+                EGL_RENDERABLE_TYPE, EGL_OPENGL_BIT,
+                EGL_NONE
+            };
+
+            desktopGL = eglChooseConfig(display, attribs, nullptr, 0, &matchingConfigs) == EGL_TRUE &&
+                        matchingConfigs > 0;
+            eglTerminate(display);
+        }
+
+        // Populate the value to return and have for next time.
+        // This can race with another thread populating the same data,
+        // but that's no big deal.
+        val = VALUE_SET | (desktopGL ? VALUE_TRUE : 0);
+        SDL_AtomicSet(&supportsDesktopGL, val);
+    }
+
+    return !!(val & VALUE_TRUE);
+#else
+    // Assume it does if we can't check ourselves
+    return true;
+#endif
+}
+
 bool WMUtils::isRunningWayland()
 {
 #ifdef HAS_WAYLAND