vulkan: Try loading libvulkan.so.1 first

Change-Id: I876899fbfc126136f2842e9361e21ac10af8f14b
Pick-to: 6.3
Fixes: QTBUG-101592
Reviewed-by: Andy Nichols <andy.nichols@qt.io>

src/gui/vulkan/qbasicvulkanplatforminstance.cpp

@@ -81,19 +81,45 @@ QBasicPlatformVulkanInstance::~QBasicPlatformVulkanInstance()
         m_vkDestroyInstance(m_vkInst, nullptr);
 }
 
-void QBasicPlatformVulkanInstance::loadVulkanLibrary(const QString &defaultLibraryName)
+void QBasicPlatformVulkanInstance::loadVulkanLibrary(const QString &defaultLibraryName, int defaultLibraryVersion)
 {
-    if (qEnvironmentVariableIsSet("QT_VULKAN_LIB"))
-        m_vulkanLib.setFileName(QString::fromUtf8(qgetenv("QT_VULKAN_LIB")));
-    else
-        m_vulkanLib.setFileName(defaultLibraryName);
+    QVarLengthArray<std::pair<QString, int>, 3> loadList;
 
-    if (!m_vulkanLib.load()) {
-        qWarning("Failed to load %s: %s", qPrintable(m_vulkanLib.fileName()), qPrintable(m_vulkanLib.errorString()));
+    // First in the list of libraries to try is the manual override, relevant on
+    // embedded systems without a Vulkan loader and possibly with custom vendor
+    // library names.
+    if (qEnvironmentVariableIsSet("QT_VULKAN_LIB"))
+        loadList.append({ QString::fromUtf8(qgetenv("QT_VULKAN_LIB")), -1 });
+
+    // Then what the platform specified. On Linux the version is likely 1, thus
+    // preferring libvulkan.so.1 over libvulkan.so.
+    loadList.append({ defaultLibraryName, defaultLibraryVersion });
+
+    // If there was a version given, we must still try without it if the first
+    // attempt fails, so that libvulkan.so is picked up if the .so.1 is not
+    // present on the system (so loaderless embedded systems still work).
+    if (defaultLibraryVersion >= 0)
+        loadList.append({ defaultLibraryName, -1 });
+
+    bool ok = false;
+    for (const auto &lib : loadList) {
+        m_vulkanLib.reset(new QLibrary);
+        if (lib.second >= 0)
+            m_vulkanLib->setFileNameAndVersion(lib.first, lib.second);
+        else
+            m_vulkanLib->setFileName(lib.first);
+        if (m_vulkanLib->load()) {
+            ok = true;
+            break;
+        }
+    }
+
+    if (!ok) {
+        qWarning("Failed to load %s: %s", qPrintable(m_vulkanLib->fileName()), qPrintable(m_vulkanLib->errorString()));
         return;
     }
 
-    init(&m_vulkanLib);
+    init(m_vulkanLib.get());
 }
 
 void QBasicPlatformVulkanInstance::init(QLibrary *lib)

src/gui/vulkan/qbasicvulkanplatforminstance_p.h

@@ -81,7 +81,7 @@ public:
     const QList<QVulkanInstance::DebugFilter> *debugFilters() const { return &m_debugFilters; }
 
 protected:
-    void loadVulkanLibrary(const QString &defaultLibraryName);
+    void loadVulkanLibrary(const QString &defaultLibraryName, int defaultLibraryVersion = -1);
     void init(QLibrary *lib);
     void initInstance(QVulkanInstance *instance, const QByteArrayList &extraExts);
 
@@ -93,7 +93,7 @@ protected:
 private:
     void setupDebugOutput();
 
-    QLibrary m_vulkanLib;
+    std::unique_ptr<QLibrary> m_vulkanLib;
 
     bool m_ownsVkInst;
     VkResult m_errorCode;

src/plugins/platforms/vkkhrdisplay/qvkkhrdisplayvulkaninstance.cpp

@@ -44,7 +44,7 @@ QT_BEGIN_NAMESPACE
 QVkKhrDisplayVulkanInstance::QVkKhrDisplayVulkanInstance(QVulkanInstance *instance)
     : m_instance(instance)
 {
-    loadVulkanLibrary(QStringLiteral("vulkan"));
+    loadVulkanLibrary(QStringLiteral("vulkan"), 1);
 }
 
 void QVkKhrDisplayVulkanInstance::createOrAdoptInstance()

src/plugins/platforms/xcb/qxcbvulkaninstance.cpp

@@ -48,7 +48,7 @@ QXcbVulkanInstance::QXcbVulkanInstance(QVulkanInstance *instance)
       m_getPhysDevPresSupport(nullptr),
       m_createSurface(nullptr)
 {
-    loadVulkanLibrary(QStringLiteral("vulkan"));
+    loadVulkanLibrary(QStringLiteral("vulkan"), 1);
 }
 
 QXcbVulkanInstance::~QXcbVulkanInstance()