fix(linux/xdgportal): avoid duplicate frame insertion (#4839)

src/platform/common.h

@@ -534,6 +534,10 @@ namespace platf {
       return true;
     }
 
+    virtual bool is_event_driven() {
+      return false;
+    }
+
     virtual ~display_t() = default;
 
     // Offsets for when streaming a specific monitor. By default, they are 0.

src/platform/linux/portalgrab.cpp

@@ -1365,6 +1365,11 @@ namespace portal {
       return 0;
     }
 
+    // This capture method is event driven; don't insert duplicate frames
+    bool is_event_driven() override {
+      return true;
+    }
+
   private:
     bool is_buffer_redundant(const egl::img_descriptor_t *img) {
       // Check for corrupted frame

src/video.cpp

@@ -1972,8 +1972,9 @@ namespace video {
       }
     });
 
-    // set max frame time based on client-requested target framerate.
-    double minimum_fps_target = (config::video.minimum_fps_target > 0.0) ? config::video.minimum_fps_target : config.framerate;
+    // set max frame time based on client-requested target framerate (or 0.5fps/2000ms for event-driven capture)
+    double def_fps_target = (disp->is_event_driven() ? 1 : config.framerate);
+    double minimum_fps_target = (config::video.minimum_fps_target > 0.0) ? config::video.minimum_fps_target : def_fps_target;
     std::chrono::duration<double, std::milli> max_frametime {1000.0 / minimum_fps_target};
     BOOST_LOG(info) << "Minimum FPS target set to ~"sv << (minimum_fps_target / 2) << "fps ("sv << max_frametime.count() * 2 << "ms)"sv;