Clock frame generation by the game's frames

With frame generation on, a scene drawn for another window (Steam's
overlay) went into the engine as a game frame. Adaptive counted it as
source rate and planned against that (36 base for a game capped at 30),
and a fixed multiplier gave it present slots while game frames were
dropped (26 -> 51 at 2x). Such a change now waits for the game's next
frame.

The HUD's base rate is the game window's own frames, as Steam's overlay
counts them, instead of the compositor's scene rate.

app/src/main/cpp/waylandcomp/src/compositor.c

@@ -750,6 +750,8 @@ static void take_shm(struct surface *s, struct wl_shm_buffer *shm, struct wl_res
 static struct surface *g_hud_surface;
 /* When the HUD's window last presented a frame (now_ns), to let a replacement take over. */
 static int64_t g_hud_last_ns;
+/* That window committed a frame the screen has not drawn yet. */
+static int g_hud_fresh;
 extern void banner_on_game_surface(const char *window, const char *gpu); /* window NULL = gone */
 extern void banner_on_game_frame(void);
 /* The program behind that window: its Linux pid (the Wayland client's credentials) and executable name
@@ -852,7 +854,7 @@ static void take_dmabuf(struct surface *s, struct dmabuf_buffer *b, struct wl_re
      * Asking whether the compositor could import it, as this used to, is a question about the
      * copy path and not about whether a frame happened: a game whose buffers go straight to
      * the display layer draws on screen while the counter sat at 0.0 fps and 1000.0 ms. */
-    if (s == g_hud_surface) { g_hud_last_ns = now_ns(); banner_on_game_frame(); }
+    if (s == g_hud_surface) { g_hud_last_ns = now_ns(); g_hud_fresh = 1; banner_on_game_frame(); }
 }
 
 /* ---- hooks for ahb_swapchain.c (zero-copy layers) */
@@ -2021,6 +2023,7 @@ static void render_scene(void) {
     int copy = 0; /* this scene went through the screen swapchain (the perf line's "copy") */
 
     g_dirty = 0;
+    g_hud_fresh = 0;
     g_hdr_unimported = NULL; /* found again while the scene is built (HDR gate open only) */
     wl_list_for_each(s, &g_surfaces, link) s->drawn = 0;
     scene_size(&w, &h);
@@ -2236,6 +2239,13 @@ static void schedule_render(void) {
     wl_event_source_timer_update(g_fallback_timer, 8);
 }
 
+/* With frame generation on, every scene is the engine's next source frame, so one drawn for
+ * another window (Steam's overlay) counted as a game frame and took its present slots. Such a
+ * change waits for the game's next frame, unless the game has been still for 100 ms. */
+static int scene_waits_for_game(int64_t now) {
+    return g_hud_surface && !g_hud_fresh && now - g_hud_last_ns < 100000000LL && vkp_framegen_active();
+}
+
 /* A screen refresh (Choreographer tick): draw the newest state once. */
 static void on_vsync(int64_t frame_time_ns) {
     int64_t now = now_ns();
@@ -2251,7 +2261,7 @@ static void on_vsync(int64_t frame_time_ns) {
     if (vkp_apply_window_request()) g_dirty = 1;
     /* A screen-effect setting changed (JNI, any thread): redraw so it shows on a static scene too. */
     if (vkp_effects_sync()) g_dirty = 1;
-    if (g_dirty) render_scene();
+    if (g_dirty && !scene_waits_for_game(now)) render_scene();
 }
 
 /* ------------------------------------------------------------------ wl_seat */

app/src/main/java/com/droiddeck/launcher/session/PerfHud.kt

@@ -21,8 +21,9 @@ import java.util.concurrent.atomic.AtomicInteger
  * is on, what the screen is actually being shown - "60 → 118 fps" is the proof that the engine
  * is doing something, and "FG starting" or a reason is the proof that it is not.
  *
- * The base rate is counted here from the compositor's per-frame callback, so it is right with or
- * without an engine. The presented rate comes from the engine's own telemetry while it generates.
+ * The base rate is the game window's own frames, counted here from the compositor's per-frame
+ * callback with or without an engine - what Steam's overlay counts too. The presented rate comes
+ * from the engine's telemetry while it generates.
  */
 class PerfHud(context: Context) {
     /** Empty when the HUD is off or not yet started. */
@@ -99,10 +100,7 @@ class PerfHud(context: Context) {
         return when {
             problem == 1 -> context.getString(R.string.hud_fg_unsupported, name)
             problem == 2 -> context.getString(R.string.hud_fg_failed, name)
-            stats != null && stats[3] > 1f -> {
-                val source = if (stats[2] > 1f) stats[2] else base
-                String.format(Locale.US, "%s  %.0f → %.0f fps", label, source, stats[3])
-            }
+            stats != null && stats[3] > 1f -> String.format(Locale.US, "%s  %.0f → %.0f fps", label, base, stats[3])
             else -> context.getString(R.string.hud_fg_starting, label, fps(base))
         }
     }