fix: exclude a caller's windows that are not on screen yet

Author: developer239

include/robot/VideoFrame.h

@@ -25,7 +25,8 @@ struct VideoFrameInfo {
   // padding, resize letterboxing), so this is part of the contract.
   LogicalRect contentRect;
   // Presentation timestamp mapped onto steady_clock (not delivery time), so
-  // frame age reflects how old the pixels actually are.
+  // frame age reflects how old the pixels actually are. macOS can deliver a
+  // frame before its display time, which makes this a few ms in the future.
   std::chrono::steady_clock::time_point capturedAt;
 };
 

src/platform/macos/MacWindowBackend.mm

@@ -209,13 +209,15 @@ - (void)streamDidBecomeInactive:(SCStream*)stream {
   return value;
 }
 
-std::expected<SCShareableContent*, Error> fetchShareableContent() {
+std::expected<SCShareableContent*, Error> fetchShareableContent(
+    const BOOL isOnScreenOnly = YES
+) {
   dispatch_semaphore_t semaphore = dispatch_semaphore_create(0);
   __block SCShareableContent* content = nil;
   __block NSError* error = nil;
   [SCShareableContent
       getShareableContentExcludingDesktopWindows:YES
-                             onScreenWindowsOnly:YES
+                             onScreenWindowsOnly:isOnScreenOnly
                                completionHandler:^(
                                    SCShareableContent* result, NSError* err
                                ) {
@@ -538,7 +540,9 @@ void stop() override {
     );
   }
 
-  auto contentResult = fetchShareableContent();
+  // Includes windows not on screen yet: a caller that creates its overlay just
+  // before streaming would otherwise not be listed, and so not be excluded.
+  auto contentResult = fetchShareableContent(NO);
   if (!contentResult) return std::unexpected(contentResult.error());
 
   SCDisplay* scDisplay = nil;