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StressPerf: WinUI 3 Update Strategy Comparison

Goal

Compare three approaches to updating a large grid of UI elements in WinUI 3, measuring FPS and memory under identical workloads.

Grid Layout

  • 80 columns x 60 rows = 4,800 cells
  • Each cell displays: SYMBOL $PRICE (e.g. AAB $142.37)
  • Cell foreground color: green if price went up, red if it went down
  • Fixed cell size: 76 x 22 px, FontSize 10
  • Grid is wrapped in a ScrollViewer

Data Model

Each cell maps to a StockItem:

Field Type Description
Symbol string 3-letter ticker (deterministic)
PrevPrice double Price before the last update
CurrentPrice double Current price
IsUp bool true if CurrentPrice >= PrevPrice

Symbols are generated deterministically from row/column indices so all three apps display identical data.

Update Loop

  1. A DispatcherTimer fires every 33 ms (~30 Hz target).
  2. On each tick, N% of the 4,800 items are randomly mutated (price changes by up to +/-2% of current value, biased slightly upward).
  3. The UI is updated according to the variant's strategy.
  4. CompositionTarget.Rendering counts actual composed frames for FPS.

Three Variants

1. Direct (StressPerf.Direct)

Baseline — minimal overhead:

  • Build a WinUI Grid with 80 columns / 60 rows at startup.
  • Store a TextBlock[] of 4,800 references.
  • On tick: loop over changed indices, set TextBlock.Text and TextBlock.Foreground directly.

2. Data-Bound (StressPerf.Bound)

Standard MVVM pattern:

  • Build identical grid at startup.
  • Each TextBlock is bound (Binding, OneWay) to a StockItemViewModel : INotifyPropertyChanged.
  • ViewModel exposes DisplayText (string) and PriceBrush (SolidColorBrush).
  • On tick: set ViewModel properties; the binding engine propagates changes.

3. Reactor Functional (StressPerf.Reactor)

Reactor's declarative reconciliation:

  • A Component holds StockItem[] in UseState.
  • Render() produces 4,800 Text(...) elements inside a Grid(...).
  • On tick: call setData(newArray) — the Reactor reconciler diffs old vs new element trees and patches only changed TextBlock controls.

This is the naive Reactor variant: plain fluent API, no memo, no direct-initializer tricks. It is what an unaware user writes and stays that way permanently — it's the framework-level baseline the spec-034 table compares the optimized variant against.

4. Reactor Perf-Tuned (StressPerf.ReactorOptimized)

Same workload, same UI, same Component/Render() shape, but the inner-loop cell construction follows the spec-034 §B/§C idioms:

  • Cells are built via direct new TextBlockElement { … } initializer with Modifiers = new ElementModifiers { Layout = …, Visual = … } buckets — bypasses the with-clone steps the fluent chain produces.
  • UseMemoCellsByIndex (Phase 4 of spec 034) skips re-running the builder for unchanged indices, so a 10% mutation tick allocates ~10% of the cells the naive variant does.

This is the optimized Reactor variant — the reference implementation of the spec-034 perf-tips skill. Do not adopt this shape for ordinary UI; restrict it to identifiable hot loops (lists/grids with hundreds-plus elements per render).

Interactive Mode (default)

Each app opens a window with:

  • Slider (0–100%) controlling the percentage of items updated per tick.
  • Start / Stop toggle button.
  • FPS and Memory readout (updated every second).
  • The stock grid below the controls.

CLI / Headless Mode

StressPerf.Direct.exe --headless --percent 50 --duration 10
Flag Default Description
--headless off Auto-start, run for duration, print report, exit
--percent 10 Percentage of cells updated per tick
--duration 10 Seconds to run before reporting

Report Output (stdout)

=== StressPerf.Direct ===
Duration:    10.0s
Percent:     50%
Avg FPS:     31.2
Min FPS:     28.4
Max FPS:     33.1
Avg Update:  2.3 ms
Max Update:  5.1 ms
Avg Memory:  142.3 MB
Peak Memory: 158.7 MB

Perf Harness (StressPerf.Shared)

Shared library consumed by all three apps:

Class Responsibility
StockDataSource Generates and mutates 4,800 StockItems
PerfTracker FPS counter, update-time recorder, memory sampler
CliOptions Parses --headless, --percent, --duration
ConsoleHelper Attaches parent console for stdout in WinExe builds

Build & Run

WinUI variants (Direct, Bound, DirectX, Reactor, ReactorOptimized, ReactorGrid, VirtualList.Reactor) target net10.0-windows10.0.22621.0 and pick up the repo-wide WindowsAppSDKVersion from Directory.Build.props. The WPF variant targets net10.0-windows; PresentTracer is plain net10.0. The shared scaffold (StressPerf.Shared) is net10.0-windows.

# Build all
dotnet build tests/stress_perf/StressPerf.Direct -c Release -p:Platform=x64
dotnet build tests/stress_perf/StressPerf.Bound  -c Release -p:Platform=x64
dotnet build tests/stress_perf/StressPerf.Reactor   -c Release -p:Platform=x64
dotnet build tests/stress_perf/StressPerf.ReactorOptimized -c Release -p:Platform=x64

# Run interactive
dotnet run --project tests/stress_perf/StressPerf.Direct -c Release -p:Platform=x64

# Run headless benchmark
dotnet run --project tests/stress_perf/StressPerf.Direct -c Release -p:Platform=x64 -- --headless --percent 50 --duration 10