Fix high DPI check in 0437835b

app/app.pro

@@ -104,6 +104,16 @@ unix:!macx {
             CONFIG += libdrm
         }
     }
+
+    packagesExist(wayland-client) {
+        DEFINES += HAS_WAYLAND
+        PKGCONFIG += wayland-client
+    }
+
+    packagesExist(x11) {
+        DEFINES += HAS_X11
+        PKGCONFIG += x11
+    }
 }
 win32 {
     LIBS += -llibssl -llibcrypto -lSDL2 -lSDL2_ttf -lavcodec -lavutil -lopus -ld3dx9
@@ -148,7 +158,8 @@ SOURCES += \
     settings/mappingmanager.cpp \
     gui/sdlgamepadkeynavigation.cpp \
     streaming/video/overlaymanager.cpp \
-    backend/systemproperties.cpp
+    backend/systemproperties.cpp \
+    wm.cpp
 
 HEADERS += \
     utils.h \

app/main.cpp

@@ -29,6 +29,7 @@
 #include "cli/startstream.h"
 #include "cli/commandlineparser.h"
 #include "path.h"
+#include "utils.h"
 #include "gui/computermodel.h"
 #include "gui/appmodel.h"
 #include "backend/autoupdatechecker.h"
@@ -287,7 +288,10 @@ int main(int argc, char *argv[])
 
     // Avoid using High DPI on EGLFS. It breaks font rendering.
     // https://bugreports.qt.io/browse/QTBUG-64377
-    if (QGuiApplication::platformName() != "eglfs") {
+    //
+    // NB: We can't use QGuiApplication::platformName() here because it is only
+    // set once the QGuiApplication is created, which is too late to enable High DPI :(
+    if (WMUtils::isRunningWindowManager()) {
         // Enable High DPI support
         QCoreApplication::setAttribute(Qt::AA_EnableHighDpiScaling);
 

app/utils.h

@@ -3,3 +3,8 @@
 #define THROW_BAD_ALLOC_IF_NULL(x) \
     if ((x) == nullptr) throw std::bad_alloc()
 
+namespace WMUtils {
+    bool isRunningX11();
+    bool isRunningWayland();
+    bool isRunningWindowManager();
+}

app/wm.cpp

@@ -0,0 +1,46 @@
+#include "utils.h"
+
+#ifdef HAS_X11
+#include <X11/Xlib.h>
+#endif
+
+#ifdef HAS_WAYLAND
+#include <wayland-client.h>
+#endif
+
+bool WMUtils::isRunningX11()
+{
+#ifdef HAS_WAYLAND
+    Display* display = XOpenDisplay(nullptr);
+    if (display != nullptr) {
+        XCloseDisplay(display);
+        return true;
+    }
+#endif
+
+    return false;
+}
+
+bool WMUtils::isRunningWayland()
+{
+#ifdef HAS_WAYLAND
+    struct wl_display* display = wl_display_connect(nullptr);
+    if (display != nullptr) {
+        wl_display_disconnect(display);
+        return true;
+    }
+#endif
+
+    return false;
+}
+
+bool WMUtils::isRunningWindowManager()
+{
+#if defined(Q_OS_WIN) || defined(Q_OS_DARWIN)
+    // Windows and macOS are always running a window manager
+    return true;
+#else
+    // On Unix OSes, look for Wayland or X
+    return WMUtils::isRunningWayland() || WMUtils::isRunningX11();
+#endif
+}