performance

# Performance Monitoring `FlatRedBallService.Default.Performance` (a `PerformanceMonitor`, `src/Diagnostics/PerformanceMonitor.cs`) tracks rolling FPS, per-phase frame timing, and a per-collision-relationship severity breakdown over a 120-frame window. **Off by default** — set `IsEnabled = true` before it records anything; until then every stat reads zero/empty. ```csharp FlatRedBallService.Default.Performance.IsEnabled = true; // later, e.g. every N frames from Screen.CustomActivity: var perf = FlatRedBallService.Default.Performance; Console.WriteLine(perf.GenerateReport()); // FPS + phase timing + collision severity, as a string var fps = perf.Fps; // .Current / .Average / .Min / .Max var worst = perf.GetCollisionReport(); // most expensive first; each row carries a PartitionStatus ``` `GenerateReport()` only builds a string — it does no I/O itself, so printing/logging/writing it is on the caller. ## Timer resolution (web) `GenerateReport()` opens with a `Platform:` line and the measured clock step (`TimerResolutionMs`, probed once via `ProfileClock.MeasureResolutionMs`). **Landmine:** browsers coarsen their clock as a Spectre mitigation — ~1ms on Firefox/Safari, ~0.1ms on Chrome — and `Stopwatch.Frequency` does not reflect it. Whole-pass totals stay accurate (start/end errors cancel), but any per-phase number smaller than one step reads as 0 or one full step and nothing between. The report warns automatically above 0.5ms. Set `PlatformLabel` from the host — the engine targets `net10.0` and cannot read `navigator.userAgent` itself. Every row in the collision report carries a `PartitionStatus`. `Unpartitioned` is the only value worth acting on, and the fix is to set the same `Factory<T>.PartitionAxis` on both sides of the relationship. `NotApplicable` means one side is not a factory, such as a `TileShapes`, a single entity, or a plain `List<T>`, so no axis setting would change it. See the `collision-relationships` skill. See `src/Diagnostics/FrameProfile.cs` for the underlying per-frame timing struct. ## Startup timing (boot, not per-frame) `FlatRedBallService.Default.StartupTiming` (a `StartupProfiler`, `src/Diagnostics/StartupProfiler.cs`) times boot and load once — for "why does my game take so long to start," not runtime FPS. Enable via `EngineInitSettings.ProfileStartup = true` passed to `Initialize`, not on the profiler itself — profiling must be on before `Initialize` opens its first phase, so there's no turning it on afterward. The report prints itself automatically, once, right after the first screen finishes loading — don't call `GenerateReport()` yourself, and it won't fire again on later screen transitions. Game code can wrap its own slow `CustomInitialize` work in `BeginPhase`/`EndPhase` to show up in the same report.