Simplify the software backend selection logic

Avoid relying on the (somewhat obsolete) capability flag. Instead, have
a clean and straightforward check based on QT_CONFIG.

In the CI, in particular for the QEMU configs that are both OpenGL and
Vulkan capable (build-wise, yuck), the software backend will be requested
explicitly in the future so this won't need to cater for that anymore.

Change-Id: Ifa100efdae208b789f6ed2a7b57330262c13284f
Reviewed-by: Eirik Aavitsland <eirik.aavitsland@qt.io>

1 files changed, 8 insertions, 7 deletions

diff --git a/src/quick/scenegraph/qsgcontextplugin.cpp b/src/quick/scenegraph/qsgcontextplugin.cpp
index 45ecb2009b..025716c2a7 100644
--- a/src/quick/scenegraph/qsgcontextplugin.cpp
+++ b/src/quick/scenegraph/qsgcontextplugin.cpp
@@ -133,14 +133,15 @@ QSGAdaptationBackendData *contextFactory()
         if (requestedBackend.isEmpty())
             requestedBackend = qEnvironmentVariable("QT_QUICK_BACKEND");
 
-        // If this platform does not support OpenGL, Vulkan, D3D11, or Metal, and no backend has been set
-        // default to the software renderer
-#if !QT_CONFIG(vulkan) && !defined(Q_OS_WIN) && !defined(Q_OS_MACOS) && !defined(Q_OS_IOS)
-        if (requestedBackend.isEmpty()
-            && !QGuiApplicationPrivate::platformIntegration()->hasCapability(QPlatformIntegration::OpenGL))
-        {
+        // If this platform does not support OpenGL, Vulkan, D3D11, or Metal, and no
+        // backend has been set, default to the software renderer. We rely on the
+        // static, build time flags only. This is to prevent the inevitable confusion
+        // caused by run time hocus pocus. If one wants to use the software backend
+        // in a GL or Vulkan capable Qt build (or on Windows or Apple platforms), it
+        // has to be requested explicitly.
+#if !QT_CONFIG(opengl) && !QT_CONFIG(vulkan) && !defined(Q_OS_WIN) && !defined(Q_OS_MACOS) && !defined(Q_OS_IOS)
+        if (requestedBackend.isEmpty())
             requestedBackend = QLatin1String("software");
-        }
 #endif
 
         // This is handy if some of the logic above goes wrong and we select