rhi: Make it possible to query the backend name beforehand

The goal is to make it possible to implement QSGRhiSupport::backendName()
in Qt Quick with just a single line:

return QString::fromUtf8(QRhi::backendName(m_rhiBackend));

instead of duplicating the strings and the logic.

Similarly, QBackingStoreRhiSupport can now drop its apiName() helper
entirely.

Change-Id: Ia8cbb1f1243539ed4d7a98e71dcc2ed56b017e40
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Andy Nichols <andy.nichols@qt.io>

src/gui/painting/qbackingstorerhisupport.cpp

@@ -232,25 +232,6 @@ QRhi::Implementation QBackingStoreRhiSupport::apiToRhiBackend(QPlatformBackingSt
     return QRhi::Null;
 }
 
-const char *QBackingStoreRhiSupport::apiName(QPlatformBackingStoreRhiConfig::Api api)
-{
-    switch (api) {
-    case QPlatformBackingStoreRhiConfig::OpenGL:
-        return "OpenGL";
-    case QPlatformBackingStoreRhiConfig::Metal:
-        return "Metal";
-    case QPlatformBackingStoreRhiConfig::Vulkan:
-        return "Vulkan";
-    case QPlatformBackingStoreRhiConfig::D3D11:
-        return "D3D11";
-    case QPlatformBackingStoreRhiConfig::Null:
-        return "Null";
-    default:
-        break;
-    }
-    return "Unknown";
-}
-
 bool QBackingStoreRhiSupport::checkForceRhi(QPlatformBackingStoreRhiConfig *outConfig, QSurface::SurfaceType *outType)
 {
     static QPlatformBackingStoreRhiConfig config;
@@ -304,7 +285,7 @@ bool QBackingStoreRhiSupport::checkForceRhi(QPlatformBackingStoreRhiConfig *outC
         }
 
         qCDebug(lcQpaBackingStore) << "Check for forced use of QRhi resulted in enable"
-                                   << config.isEnabled() << "with api" << apiName(config.api());
+                                   << config.isEnabled() << "with api" << QRhi::backendName(apiToRhiBackend(config.api()));
     }
 
     if (config.isEnabled()) {

src/gui/painting/qbackingstorerhisupport_p.h

@@ -44,7 +44,6 @@ public:
     static bool checkForceRhi(QPlatformBackingStoreRhiConfig *outConfig, QSurface::SurfaceType *outType);
 
     static QRhi::Implementation apiToRhiBackend(QPlatformBackingStoreRhiConfig::Api api);
-    static const char *apiName(QPlatformBackingStoreRhiConfig::Api api);
 
     QRhi *rhi() const { return m_rhi; }
 

src/gui/rhi/qrhi.cpp

@@ -5456,11 +5456,12 @@ QRhi::Implementation QRhi::backend() const
 }
 
 /*!
-    \return the backend type as string for this QRhi.
+    \return a friendly name for the backend \a impl, usually the name of the 3D
+    API in use.
  */
-const char *QRhi::backendName() const
+const char *QRhi::backendName(Implementation impl)
 {
-    switch (d->implType) {
+    switch (impl) {
     case QRhi::Null:
         return "Null";
     case QRhi::Vulkan:
@@ -5474,7 +5475,15 @@ const char *QRhi::backendName() const
     }
 
     Q_UNREACHABLE();
-    return nullptr;
+    return "Unknown";
+}
+
+/*!
+    \return the backend type as string for this QRhi.
+ */
+const char *QRhi::backendName() const
+{
+    return backendName(d->implType);
 }
 
 /*!

src/gui/rhi/qrhi_p.h

@@ -1701,6 +1701,7 @@ public:
 
     Implementation backend() const;
     const char *backendName() const;
+    static const char *backendName(Implementation impl);
     QRhiDriverInfo driverInfo() const;
     QThread *thread() const;
 

tests/auto/gui/rhi/qrhi/tst_qrhi.cpp

@@ -255,6 +255,7 @@ void tst_QRhi::create()
 
         QCOMPARE(rhi->backend(), impl);
         QVERIFY(strcmp(rhi->backendName(), ""));
+        QVERIFY(!strcmp(rhi->backendName(), QRhi::backendName(rhi->backend())));
         QVERIFY(!rhi->driverInfo().deviceName.isEmpty());
         QCOMPARE(rhi->thread(), QThread::currentThread());