Run in native resolution on Retina displays when streaming above scaled resolution

app/streaming/session.cpp

@@ -620,8 +620,24 @@ void Session::updateOptimalWindowDisplayMode()
     SDL_DisplayMode desktopMode, bestMode, mode;
     int displayIndex = SDL_GetWindowDisplayIndex(m_Window);
 
-    // Get the native desktop resolution
+    // Try the current display mode first. On macOS, this will be the normal
-    if (StreamUtils::getRealDesktopMode(displayIndex, &desktopMode)) {
+    // scaled desktop resolution setting.
+    if (SDL_GetDesktopDisplayMode(displayIndex, &desktopMode) == 0) {
+        // If this doesn't fit the selected resolution, use the native
+        // resolution of the panel (unscaled).
+        if (desktopMode.w < m_ActiveVideoWidth || desktopMode.h < m_ActiveVideoHeight) {
+            if (!StreamUtils::getRealDesktopMode(displayIndex, &desktopMode)) {
+                return;
+            }
+        }
+    }
+    else {
+        SDL_LogWarn(SDL_LOG_CATEGORY_APPLICATION,
+                    "SDL_GetDesktopDisplayMode() failed: %s",
+                    SDL_GetError());
+        return;
+    }
+
     // Start with the native desktop resolution and try to find
     // the highest refresh rate that our stream FPS evenly divides.
     bestMode = desktopMode;
@@ -653,7 +669,6 @@ void Session::updateOptimalWindowDisplayMode()
 
     SDL_SetWindowDisplayMode(m_Window, &bestMode);
 }
-}
 
 void Session::toggleFullscreen()
 {